Studies and synthetic applications of the O-stannyl ketyl-promoted cyclopropane fragmentations

MISSING IMAGE

Material Information

Title:
Studies and synthetic applications of the O-stannyl ketyl-promoted cyclopropane fragmentations
Physical Description:
vii, 122 leaves : ; 29 cm.
Language:
English
Creator:
Jia, Zhaozhong J., 1968-
Publication Date:

Subjects

Subjects / Keywords:
Chemistry thesis, Ph. D   ( lcsh )
Dissertations, Academic -- Chemistry -- UF   ( lcsh )
Genre:
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1996.
Bibliography:
Includes bibliographical references (leaves 114-120).
Additional Physical Form:
Also available online.
Statement of Responsibility:
by Zhaozhong J. Jia.
General Note:
Typescript.
General Note:
Vita.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 026323620
oclc - 36664048
System ID:
AA00025761:00001

Full Text









STUDIES AND SYNTHETIC APPLICATIONS OF THE
0-STANNYL KETYL-PROMOTED CYCLOPROPANE FRAGMENTATIONS











By


ZHAOZHONG J. JIA


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY


UNIVERSITY OF FLORIDA


1996

























To the memory of my grandfather













ACKNOWLEDGMENTS


I owe thanks to many people in the chemistry department for the
completion of this dissertation. First and foremost, I would like to thank my
mentor and research director, Professor Eric Enholm, for all of his guidance,
teaching, encouragement and support throughout graduate school. I greatly
appreciate his hard efforts to help me grow into an organic chemist hand-by-
hand. I appreciate his immeasurable help in the preparation of this manuscript.
I thank the organic chemistry faculty, especially Professors Merle Battiste,
William Dolbier and Tomas Hudlicky, for their enthusiasm and inspiring
teaching to widen my knowledge and sharpen my thinking and understanding
in organic chemistry. I thank Professor Jim Deyrup for offering me admission to
such an outstanding chemistry department and for his kind help when I first
arrived in this country alone and knew nobody.
All the people in the Enholm group played a role in the completion of this
dissertation and are acknowledged. Yongping Xie and Jeff Scheier worked
patiently to improve my lab skills. Paul Whitley has been a good friend and
constant source of fun and intellectual stimulation over the past four years.
Kelley Moran, Jim Schulte II, Stan Toporek, Jennifer Lombardi and Maria
Gallagher contributed to the stimulating and friendly environments of our lab
and made lots of hard working hours more pleasurable.
I thank Ion Ghiviriga and Fernando Gomez for their help on NOE and 2-D
NMR studies. I thank Lucian Boldea, Patricia Bottari and Ivani Malvestiti, our lab








neighbors, for their friendship and generosity in lending me their chemicals and
glove box.
My special thanks go to Xiaoxin Rong, my former roommate and one of
my best friends here. He made me quickly adjusted to the American culture,
assisted me to shop for my first car and trained me to drive, and always was
there to help me through my difficult times.

None of this would have been possible without my family's love. I thank
my parents and grandparents for their enlightening guidance and endless

encouragement and support to help me grow up and acquire more knowledge
and better education. They and my uncles and aunts all supported me with their
savings to generously sponsor my graduate school applications and my first trip
to Florida from China. I thank my wife Yaping, for her enduring love,
understanding and help during my graduate studies and the preparation of this

dissertation.
Finally I would like to acknowledge the National Science Foundation for
its financial support to the work described in this dissertation.













TABLE OF CONTENTS

AC KNO W LEDG M ENTS ................................................................................................. iii

A B S T R A C T .......................................................................................................................vi

CHAPTER

1 INTRO D UCT IO N ............................................................................................... 1

2 STUDIES OF THE 0-STANNYL KETYL-PROMOTED
CYCLOPROPANE FRAGMENTATIONS.................................................... 24

3 APPLICATIONS OF THE 0-STANNYL KETYL-PROMOTED
CYCLOPROPANE FRAGMENTATIONS TO THE SYNTHESIS
OF TRIQUINANE COMPOUNDS................................................................. 53


4 OTHER INVESTIGATIONS OF THE 0-STANNYL KETYL-
PROMOTED CYCLOPROPANE FRAGMENTATIONS............................. 68
Application of the Post-Fragmentation Tin(IV) Enolates................. 68
Cyclopropane Fragmentation-Allylation by Allyltributyltin ............. 72


5 S U M M A RY ....................................................................................................... 78

6 EXPERIM ENTAL............................................................................................. 80
G general M ethods................................................................................... 80
Experimental Procedures and Results.............................................. 81

LIST O F REFER ENC ES ............................................................................................. 114

BIO G RAPHICAL SKETCH ......................................................................................... 121













Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

STUDIES AND SYNTHETIC APPLICATIONS OF THE
0-STANNYL KETYL-PROMOTED CYCLOPROPANE FRAGMENTATIONS

By

Zhaozhong J. Jia

December, 1996



Chairman: Eric J. Enholm
Major Department: Chemistry

This dissertation investigated the 0-stannyl ketyl-promoted cyclopropane
fragmentations. 0-stannyl ketyls were generated by the reactions of cyclopropyi
ketones with tributyltin hydride or allyltributyltin. The goal of this study was to

examine the reactivities of these cyclopropanes and examine the mechanistic
attributes governing the cyclopropane fragmentation process, such as
stereoelectronic effects and radical-stability effects. Another goal of this study

was to apply the 0-stannyl ketyl-promoted cyclopropane fragmentations to

organic synthesis.
The first area of study was the 0-stannyl ketyl-promoted cyclopropane
fragmentations using tributyltin hydride. A variety of cyclopropyl ketone
precursors were examined, including tricyclo[3.3.0.02,8]octan-3-one substrates.
These fragmentations were governed by both stereoelectronic effects and

radical-stability effects.








The second area of study was the synthetic applications of the 0-stannyl
ketyl-promoted cyclopropane fragmentations. The 0-stannyl ketyl-promoted
cyclopropane fragmentation-cyclization tandem sequence was accomplished.
The efficient synthesis of two triquinane molecules demonstrated this tandem
sequence and a novel synthetic methodology for triquinane compounds.

The third area of study included the preliminary work on the tin(IV)
enolates generated in the cyclopropane fragmentations. Their applications in
aldol and alkylation reactions were successful. Allyltributyltin-induced
cyclopropane fragmentation-allylation reactions were also preliminarily

examined.













CHAPTER 1
INTRODUCTION


The term "free radical" applies to a species possessing one unpaired
electron.1 A free radical is generated by homolytic cleavage of a covalent bond.
The central atom is usually sp2 hybridized and the unpaired electron resides in
the p-orbital.2 Though free radicals are highly reactive intermediates, reactions
involving them generally embrace mild reaction conditions, in contrast to the
harsh reaction conditions associated with the generation of cations or anions.
Free radical chemistry dates back to 1900 when Gomberg investigated
the formation and reactions of triphenylmethyl radical.3 However, free radicals
had little synthetic use until the 1970s.4 In that decade, new synthetic methods
involving free radicals began to be developed. The understanding and synthetic
applications of radicals have grown quickly since. Today free radical reactions
have been a routine method to accomplish constructions of a wide variety of

carbon and hetereoatom skeletons.5
Organotin compounds have been extensively studied for decades.6

Among them, tributyltin hydride (TBTH) has been known for over 30 years to
engage in free radical reactions. It is commercially available and can be readily
prepared as well.6,7 Tin has a 5s25p2 electronic configuration and exists in
tetrahedral sp3 hybridization in TBTH. The Sn-H bond in TBTH is of 0.17 nm in
length and 73.7 kcal/mol in bond dissociation energy (BDE).6d,g,8 This bond
can be homolytically-cleaved with a radical initiator to produce a tributyltin







radical. Azo and peroxide compounds are common free radical initiators,
possessing a weak C-N bond or 0-0 bond, as shown in Figure 1-1.2a


Temperature for
Name Structure BDE (kcal/mol) 1-hr Half-life (C)

AIBN NC--N=N--CN 30 85


acetyl 0 0
peroxide Me -"- 0-0-"- Me 30-32 85

benzoyl 0 0
peroxide Ph-1--0 1LPh 30 95

t-butyl 0-0- 37 135
peroxide+

peroxide 0-0 37 150


Figure 1-1
Common free radical initiators

The combination of TBTH 1 and initiator AIBN (azobisisobutylnitrile) 2 in
refluxing benzene (80C) is the most popular way to generate tributyltin radical.
As shown in Scheme 1-1, thermal decomposition of AIBN produces
cyanoisopropyl radical 3, which abstracts a hydrogen atom from the Sn-H bond


N N=N-AN
NC+ N=N 2


CN


+ N2


+ H-SnBu3


H
CN


+ *SnBu3

5


Scheme 1-1


.K
CN
3







of TBTH to give tributyltin radical 5.
There are five broad classes of free radical reactions,9 as shown in
Scheme 1-2: i) radical combination (coupling) (eq. 1); ii) radical abstraction of
an atom or group (eq. 2); iii) radical addition to a multiple bond (eq. 3); iv)
radical fragmentation (3-elimination), the reverse process of addition (eq. 4); v)

radical rearrangement (eq. 5).


R- + *A R-A (eq.1)

R- + A-B R-A + *B (eq.2)

R- + A=B R-A-B. (eq.3)

R-A-B. -- R. + A=B (eq.4)

R-A-B. -- *A-B-R (eq.5)

Scheme 1-2

Bu3Sn. + R-X -- Bu3Sn-X + R-
5 6 7 8


R- + Bu3SnH -- R-H + Bu3Sn-
8 1 9 5

Scheme 1-3


The atom or group abstraction reactions (eq. 2) of tributyltin radicals are
very useful. Halide abstraction is of great synthetic importance.6g Bromide and
iodide are most commonly used. As shown in Scheme 1-3, halide reduction
occurs through a chain mechanism. Tributyltin radical 5 abstracts halogen atom
X from halide 6, generating carbon-centered radical 8. Radical 8 abstracts a
hydrogen atom from TBTH, giving reduction product 9 and another tributyltin







radical to carry on this chain reaction. Depending on its structure, radical
intermediate 8 may undergo addition, fragmentation or rearrangement
reactions before the final hydrogen abstraction occurs.
TBTH reduces thiols, thioethers and selenides as well, due to the
formation of strong Sn-S or Sn-Se bonds.6g Barton developed this reduction
into a powerful deoxygenation method,10 which can be applied to a wide
variety of hydroxy compounds, including primary, secondary, tertiary alcohols
and diols. The general sequence of a Barton deoxygenation is shown in
Scheme 1-4. This reaction proceeds through an addition of tributyltin radical to
the thiocarbonyl group, followed by fragmentation of carbon-centered radical
12 to liberate alkyl radical 8 and restore the carbonyl function. Radical 8
abstracts a hydrogen atom from TBTH, giving reduction product 9. The Y group
can be hydrogen, methyl, phenyl, S-methyl, S-phenyl, 0-phenyl and
imidazolyl.6g
SnBu3
S S

R-OHR Bu3SnR. R,
RO 0 Y o Y

10 11 12
,SnBu3
S
| + R. TBTH R-H
--^A+ R-- *PH
0"" Y Bu3Sn.
13 8 9

Scheme 1-4


The addition of a free radical to a multiple bond constructs a new a-bond
at the cost of a t-bond, as shown by eq. 3 in Scheme 1-2. Though this addition
is energetically favorable, it is still considered reversible. The rate of this radical
addition is influenced by the stabilities of R,, multiple bond A=B, and radical








RAB. formed by the addition; steric hindrance to the addition step; and polar
factors.2a The substituents on Re and on the multiple bond play important roles

in this addition. These substituent effects can be understood through the frontier

molecular orbital (FMO) theory.11 1 2
In the FMO theory, patterns of reactivity can often be addressed in terms
of interactions between the FMOs in the two reacting species. The FMO of a free
radical is its "singly occupied" molecular orbital (SOMO). The FMOs of a
multiple bond are its "highest occupied" molecular orbital (HOMO) and "lowest
unoccupied" molecular orbital (LUMO).12 A very important determinant of the
activation energy of this reaction is the SOMO-HOMO and SOMO-LUMO
interactions. Since orbital interaction is stronger for orbitals of comparable
energy, one of these two interactions is usually more significant than the other if
the SOMO-HOMO energy gap and the SOMO-LUMO energy gap are not equal.
Any substituent on either the radical or the multiple bond lowering the SOMO-
HOMO or SOMO-LUMO energy gap lowers the activation energy of this

addition.11,12
The electronic characteristics of radicals and multiple bonds are defined
as the following. An "electrophilic" radical, possessing an electron-withdrawing-
group (EWG) substituent, has an energy-lower SOMO. A "nucleophilic" radical,
possessing an electron-donating-group (EDG) substituent, has an energy-
higher SOMO. An "electron-rich" multiple bond, possessing an EDG, has an
energy-higher HOMO. An "electron-deficient" multiple bond, possessing an
EWG, has an energy-lower LUMO.12
A favorable SOMO-HOMO or SOMO-LUMO interaction is required for a
radical addition reaction to occur, as shown in Figure 1-2. For an electrophilic
radical (low SOMO), its interaction with the HOMO is usually more significant
than that with the LUMO. For a nucleophilic radical (high SOMO), the SOMO-





6

LUMO interaction is usually stronger than the SOMO-HOMO interaction.11 Alkyl

radical is nucleophilic, and its interaction with a receiving multiple bond is thus

mainly in a SOMO-LUMO manner.


S-- LUMO
A. A=B

R.
I


4 HOMO

A=B
SOMO-HOMO interaction


-- LUMO
,'/A=B
SOMO-Rf, '
R -

-4- HOMO
A=B
SOMO-LUMO interaction


Figure 1-2
Orbital interactions of a radical with a multiple bond (eq. 3)


16 Y

H


V--- Bu3SnX 7
8 R



14
15


Scheme 1-5


Formation of carbon-carbon bonds is the heart of organic synthesis. With
a new carbon-carbon bond constructed, the addition of an alkyl radical to an
alkene or alkyne is synthetically important.1 For this radical intermolecular
addition to be successful, a selectivity requirement must be fulfilled. This
requirement pertains to intermediates 5, 8, and 15 (Scheme 1-5).1 Each







intermediate should have a specific partner to react with. If 8 and 15 have the
same tendency to add to alkene 14, polymerization can result. To prevent
polymerization, the electronic characteristics of 8 and 15 must be opposite in
nature so that they have different reactivities towards alkene 14.
To fulfill the selectivity requirement, a combination of nucleophilic alkyl
radical 8 and electron-deficient alkene 14 (Y=EWG) is popular.13 Nucleophilic
8 readily reacts with 14, producing electrophilic 15. This radical does not react
with electron-deficient 14 and will eventually be quenched by TBTH to give 16.
The reaction of eq. 5 (Scheme 1-6) is such an example. Alkene 18 is electron-
deficient, due to the cyano group. Under TBTH treatment iodide 17 provides
nucleophilic cyclohexyl radical. However, the combination of electrophilic 8 and
electron-rich 14 (Y=EDG) works well too. As shown in eq. 6, 21 is electron-rich,
and electrophilic radical is generated from chloride 20.


CN
+ =TBTH (eq.5)
CN 95% /
17 18 19

RO2C TBTH RO2C
)-Cl + \ > y (eq. 6)
RO2C OC4H9 60% RO2C OC4H9

20 21 22

Scheme 1-6


After a new carbon-carbon bond forms in an addition, adduct radical 26
can be transformed into a non-radical product not only by a hydrogen
abstraction from TBTH, but also by homolytically cleaving a P-bond to split off
radical 26, as shown in Scheme 1-7.1 This fragmentation prevents radical 24







from reacting with alkene 23. If this P-elimination is fast enough, radicals 8 and

24 need not to be of different electronic characteristics.


R- + R",,, Y R. + y.

8 23 24 25 26

Scheme 1-7


Keck's allylation reactions involve such a P-elimination.14 Keck used
allyltributyltin 27 to intermolecularly accept alkyl radical 8, as shown in Scheme
1-8. Once adduct 28 forms, the C-Sn bond 3 to the radical center rapidly

fragments, giving tributyltin radical 5 and allylated product 25. Radical 5 then
abstracts the X group from 6, reproducing alkyl radical 8 to renew the reaction
cycle. Substrate 6 can be a halide, thioether, selenide or xanthate. A variety of
substrates 6, including carbohydrate derivatives, can be applied (Scheme 1-
9).14


AIBN Bu3Sn 27


SnBu3 R-X
25 6
25 R/ SnBu3

28
Bu3Sn 7R. I Bu3SnX
27 8 7


Scheme 1-8









0 0
0 0
0 X r /\,SnBu3 .0.,

^AIBN
0 0 80-90% 05 0

29 (X=CI, SPh) 30

OH OH
HO,, 1,OBz 3h HO,. .,,OBz
hv
MeO" Br01 91% MeO'"' 0
31 32

Scheme 1-9


"Cyclizations" are intramolecular additions. A typical 5-hexenyl radical
cyclization is shown in Scheme 1-10.1 The cyclization rate constant of 5-
hexenyl radical 34 to cyclopentylmethyl radical 35 is about 105 s-1 at 25C. It


H 1 Bu3SnH ,AIBN Br

36 ScnBu3 33
5
1 Bu3SnH Bu3SnX 7


34
35 S 1-10

Scheme 1-10







can be further increased by making the alkene electron-deficient with an EWG
substituent.15 Although radicals 34 and 35 have the same nucleophilicity, the
selectivity requirement for chain reactions can still be fulfilled: 34 cyclizes to the
alkene, whereas 35 only reacts with TBTH in an intermolecular manner.

Free radical cyclizations are powerful methods for five- and six-
membered ring constructions. Molecular geometry is a key factor to influence

the regioselectivity and stereochemistry of the cyclizations. The cyclizations of
5-hexenyl radical 34 have been extensively studied and proceed in a highly
regioselective manner.16,17 In almost all cases, 5-hexenyl radicals
preferentially engage in 5-exo cyclizations, following Baldwin's rule.18 The 5-
exo cyclization product 35 forms faster than the 6-endo product 37 in a ratio of

50:1, as shown in Scheme 1-11.16






(50:1)
34 35 37

Scheme 1-11




+



Figure 1-3
Beckwith's chair transition state for 5-hexenyl radical cyclization


According to Beckwith, 5-hexenyl radical cyclization proceeds through a
chair-like transition state (Figure 1-3), with substituents preferring pseudo-







equatorial positions on the six-membered ring.16 The stereochemistry of the
major cyclization product is determined by this chair-like transition state, as

demonstrated by the examples in Scheme 1-12.1







73% 27%
38 39 40





H H H H
79% 10% 7% 4%
41 42 43 44 45

Scheme 1-12


"Fragmentation" is the reverse process of an addition. The P-elimination

of tributyltin radical in Keck's allylation (Scheme 1-8) is a radical fragmentation.
A new radical and a new multiple bond are generated in the homolytic cleavage
of a a-bond. The cleavage of an adjacent strained ring, such as a cyclopropane,

cyclobutane or epoxide, is a special type of radical fragmentation, as shown in
Scheme 1-13. The strain energy in a simple cyclopropane is 28.3 kcal/mol,
while that in a simple cyclobutane is 27.4 kcal/mol and that in a simple epoxide
is 27.2 kcal/mol.19 Though these free radical ring cleavage and closure
processes are considered reversible, the ring cleavage occurs at a much higher
rate to release ring strains.1,15a,b For example, the rate constant for ring
opening of cyclopropylcarbinyl radical 46 (Y=CH2) to allylcarbinyl radical 47







(Y=CH2) is 1.3 x 108 s-1 at 25C, while the rate constant for the reverse process

is only 4.9 x 103 s-1.15a


46



48


47



49


Scheme 1-13


A simple strained-ring fragmentation is of limited synthetic importance.
However, when this fragmentation couples with another free radical reaction, a
variety of tandem sequences can result.20


"CO2R TBTH


4IICO2R


0

TBTH
*C02R" Bu3Sn
5 CO3R
53


0



C02R
54


Scheme 1-14


Dowd demonstrated an interesting "cyclization-fragmentation" tandem
sequence, as shown in Scheme 1-14.21 In this process, radical 51 first adds to







the carbonyl, giving cyclopropane 52. Due to the ring strain, this cyclopropane
is unstable and fragments to afford ester-stabilized radical 53, which abstracts a
hydrogen from TBTH to give 54 and a tributyltin radical to renew the reaction
cycle. This sequence expands cyclohexanone 50 to cycloheptanone 54.
A free radical "fragmentation-cyclization" sequence was accomplished by
Motherwell, as shown in Scheme 1-15.22 Radical 56 cleaves the adjacent
cyclopropane, giving radical 57 which cyclizes onto an alkyne ether to construct
a spiro ring skeleton. Vinyl radical 58 reacts with TBTH to abstract a hydrogen
atom in the final step.


S

0 N- TMS




55 TMS 56
TMS

*~. ,.-TBTHH
Bu3Sn. H
57 58 59

Scheme 1-15


Boger realized a radical "cyclization-fragmentation-cyclization" tandem
sequence, as shown in Scheme 1-16.23 Unstable cyclopropane intermediate
62 first forms through a radical cyclization onto the carbonyl. The cyclopropane
fragments to produce tertiary radical 63 which is captured by an alkyne tether in
the following 5-exo-dig cyclization.














62 Ph


Ti Me
Ph


TBTH
Bu3Sn.

Ph


Scheme 1-16


67 68


STBTH
1H -P- HO
Bu3Sn.
Me


Me


-H
"H

Me


Scheme 1-17


Free radical-induced epoxide fragmentation offers a convenient method
to generate reactive oxygen-centered radicals.1 This epoxide fragmentation

also can be used in synthetically useful tandem sequences, as demonstrated in
Scheme 1-17.24 A radical is generated a to epoxide in 67. The epoxide's C-O







bond selectively cleaves, giving oxygen-centered radical 68. Through a 1,5-
hydrogen migration, radical 68 intramolecularly abstracts a hydrogen atom,
affording carbon-centered radical 69. Radical 69 cyclizes onto the olefin to
produce bicycle 70.
TBTH reduces aldehydes and ketones to alcohols.6g Depending on
reaction conditions, two different mechanisms are postulated for the initial
hydrostannation step of the reduction, as shown in Scheme 1-1 8.6g When polar
solvent and Lewis acid catalyst are used, the ionic pathway dominates (eq. 7).
In this mechanism, TBTH acts as a hydride donor, giving intermediate 73 which
reorganizes to afford tin alkoxide 74. The tin moiety is subsequently released
by hydrolysis with water, alcohols or acids, yielding alcohol.


0 Lewis 0 OSnBu3
Acid (+.7
+ H-SnBu3Polar A Bu3Sn+ .... (eq. 7)
Solvent H H
72 1 73 74

0AIBN OSnBu3 TBTH OSnBu3
i + H-SnBu3 (eq. 8)
PhH Bu3Sn
H
72 1 75 74

Scheme 1-18


A free radical pathway is postulated when the combination of TBTH and
AIBN in benzene is used (eq. 8).6g 0-stannyl ketyl radical 75 initially forms
through the addition of oxophilic tributyltin radical to carbonyl 72. This carbon-
centered ketyl radical 75 abstracts a hydrogen from TBTH, producing tin
alkoxide 74 and regenerating tributyltin radical to renew the reduction process.
Alcohol product is obtained by hydrolysis of 74.







The chemistry of 0-stannyl ketyls is the focus of this dissertation. An 0-
stannyl ketyl can be viewed as a pseudo-protected radical anion, because the
0-Sn bond has a certain degree of ionic character, due to the electronegativity
difference between oxygen and tin (Scheme 1-19). The early investigations of
this chemistry in the 1970s were mainly concentrated on mechanistic studies of
the 0-stannyl ketyl-promoted fragmentations of simple cyclopropyl ketones and
ap3-epoxyketones.6g,25 It was not until the mid-1980s when chemists finally

began to examine 0-stannyl ketyls for a synthetic purpose.


5+ +
,.SnBu3 8-.SnBu3 SnBu3
00 0


75 76 77

Scheme 1-19
The year 1985 welcomed the earliest synthetic work on 0-stannyl ketyls.
Tanner performed a series of investigations to study ketone reduction by
organotin hydrides.26 0-stannyl ketyl-promoted cyclopropane fragmentations
were once again examined using cyclopropyl phenyl ketone. Rahm studied the
effect of high pressure on ketone reduction by TBTH, including cyclopropyl
ketones and a,3-epoxyketones.27

In 1986, Beckwith accomplished the cyclization of 0-stannyl ketyl onto a
multiple bond, as shown in Scheme 1-20.28 Though the yield was excellent,
this reaction was sluggish and required excess TBTH. It took 40 hours for the
cyclization to complete. Similar 0-stannyl ketyl cyclizations were reported by

Julia (1987) and by Ueda (1988).29,30









^^OSnBu3


CO2Me
79


OSnBu3



CO2Me
80


ROH
90%


CO2Me
81


CO2Me
82


Scheme 1-20


Enholm has been actively engaged in the synthetic studies of 0-stannyl
ketyls since 1989.31-37 He envisioned that the cyclization of nucleophilic 0-
stannyl ketyl would be much faciliated if the ketyl-accepting multiple bond was
electron-deficient.31 Enholm demonstrated that aldehydes and ketones could
readily cyclize onto tethered olefinic appendages under treatment of TBTH and


TBTH +)C02Me +
C2 AIBN 81.%4
81% OH
84


CO2Me

TBTH
AIBN
69%


H (58:42)
H (58:42)


(76:24)


87 88


Scheme 1-21


CO2Me
78


TBTH
- Bu3Sn.







AIBN, as shown in Scheme 1-21.31 Both 5-exo and 6-exo cyclizations of olefins
"activated" by an EWG substituent, such as an ester, nitrile or phenyl, were

achieved.


TBTH Bu3SnO"
75% Ph

90 II


(eq. 9)


TBTH
- 56%

OSnBu3 94

HO C(Me
+
HO(41
/\ (4:1)


CO2Me


Bu3SnO
95

CO2Me

HO O (eq. 10)


97


Scheme 1-22


Enholm realized 0-stannyl ketyl-promoted tandem radical cyclizations.32
He synthesized spiro (eq. 9) and fused (eq. 10) bicycles, as shown in Scheme
1-22. Activated olefin engaged in the first cyclization. Nucleophilic 0-stannyl


O 93







ketyl radical cyclized onto this electron-deficient olefin, affording electrophilic
radical (92 and 95) which cyclized onto the electron-rich olefin tether.


0 OSnBu3

STBTH Ri
AIBN"
R R3 R2 R3
98 99


OSnBu3 OSnBu3

, TBTH RI,
R- Bu3Sn. ,
R2 R3 R2 I R3
100 101


Scheme 1-23


Enholm examined allylic 0-stannyl ketyls 99, produced by the reaction of
cx,13-unsaturated carbonyls with TBTH, as shown in Scheme 1-23.33,34 Allylic
ketyl radical 99, once generated, enjoys resonance with the adjacent olefin
moiety to give 100, a combination of tin(IV) enolate and free radical. Enholm
demonstrated that this free radical could be intramolecularly captured by an
olefin tether, as shown in Scheme 1-24.33


,CO2Me


OSnBu3


102


H
OSnBu3
105


CO2Me


103 104


QHo...P ..IH
I (2.1:1)
SCO2Me OH O

106 107


Scheme 1-24


TBTH
- Bu3Sn-







Enholm discovered that for allylic 0-stannyl ketyls, after free radical 100
was quenched by a hydrogen abstraction from TBTH, tin(IV) enolate 101 could
undergo a variety of interesting reactions, including intramolecular (eq. 11) and
intermolecular (eq. 12) aldol condensation and alkylation reactions (eq. 13), as
shown in Scheme 1-25.34 These observations are in direct contrast to how an
oa,-unsaturated ketone is normally viewed in free radical reactions, where it
often functions as electron-deficient radical acceptor in a 1,4-addition manner.


Bu3SnO 0
TBTH H
81%
109


0. H OH
__ Heq. 11)

110


0 OSnBu3 0 OH
6 TBTH PhCHO A
\ I 79% Ph
111 112 113
0 OSnBu3 0

TBTH VBr A
HMPA
71%
114 115 116


(eq. 12)





(eq. 13)


Scheme 1-25


0-stannyl ketyls are suitable for cyclizations with hetereoatom-substituted
carbon-carbon double bonds or carbon-nitrogen double bonds, demonstrated
first by Ueda in 1988.30 Kim observed 0-stannyl ketyl cyclization onto imine.38
Shibuya achieved cyclization with oxazolidinone as the ketyl acceptor (eq. 14,
Scheme 1-26).39 Naito reported cyclization of 0-stannyl ketyl with oxime ether


108







119 (eq. 15).40 Lee found that f3-alkoxyacrylate 121 was an efficient ketyl
acceptor, and accomplished the synthesis of fused oxacycle 123 (eq. 16).41

0 HO
/ r TBTH / r
<-- O 0 (eq. 14)
V N,, AIBN V N,v
86% / '
BnO 0 BnO 0
117 118
H
0 N HO N-OMe
N OMeTBTH BnO (eq. 15)
BnO"'" 'OBn AIBN BnO'", 'OBn
O1 68% A
OBn OBn
119 120
H
I'" CO2EtTBTH CO2Et r (q
I02BN + 0 (eq. 16)
S91% '"OH (46:54)
121 122 123

Scheme 1-26

The 1990s witnessed the reinvestigation of 0-stannyl ketyl-induced
epoxide fragmentations. Hasegawa reported the selective C-O bond cleavage
of a,p-epoxy ketones by thermal and photochemical reactions with TBTH.42
Bowman studied the epoxide fragmentation in 2-ketobicyclo[2.2.1]heptan-3-
spiro-2'-oxirane substrates and reached the same conclusion.43 Rawal and
Kim accomplished an interesting tandem sequence using this fragmentation, as
shown in Scheme 1-27.44 Similar to that in Scheme 1-19, this sequence
started from selective cleavage of the epoxide's C-O bond, giving reactive
oxygen-centered radical 126, which promoted a 1,5-hydrogen abstraction and







a radical cyclization. Tributyltin radical was ejected from rearranged 0-stannyl
ketyl 128 to restore the original carbonyl function.

0 OSnBu3 OSnBu3
Ph Ph NH Ph
TBTH

AIBN
72%
124 125 126
OSnBu3 OSnBu3 Ph 0 Ph

P Ph (Uj> u3Sn- r V2

OH OH OH
127 128 129
Scheme 1-27


Free radicals have been among the most extensively used intermediates
in organic synthesis.5 Unfortunately, 0-stannyl ketyl is much less studied and
still poorly understood. As pointed out before, although the 0-stannyl ketyl-
promoted cyclopropane fragmentation has been known for over 25 years,25
this reaction was only examined using simple molecules for mechanistic
interests. No synthetic application of this fragmentation had ever been reported
prior to the work described in this dissertation. In order to continue the
exploration and understanding of 0-stannyl ketyls, this dissertation investigates
the 0-stannyl ketyl-promoted cyclopropane fragmentations with a wide variety
of substrates. This dissertation demonstrates a novel 0-stannyl ketyl-initiated
cyclopropane fragmentation-cyclization tandem sequence and applies it to the
efficient synthesis of two triquinane molecules. This dissertation also examines
the chemistry of tin(IV) enolates, produced in cyclopropane fragmentations.








Chapter 2 describes the studies of 0-stannyl ketyl-promoted
cyclopropane fragmentations using simple, bicyclic and tricyclic substrates. A
special tricyclic substrate, tricyclo[3.3.O.02,8]octan-3-one, was treated with
TBTH to produce different ring cleavage products, depending on the location
and type of substituent present. An examination of both radical-stabilizing
substituents and stereoelectronic effects was carried out to understand which
factors biased the bond cleavage in a rigid a-ketocyclopropane.

Chapter 3 examines the tandem sequence arising from 0-stannyl ketyl-
promoted cyclopropane fragmentation and following radical cyclization. This
radical tandem sequence gave high yields in good stereoselectivity. This work
accomplished the novel synthesis of an angular and a linear triquinane model
compound. This is the first ever known example of the 0-stannyl ketyl-initiated
cyclopropane fragmentation-cyclization tandem reactions.
Chapter 4 demonstrates the applications of tin(IV) enolates generated in
cyclopropane fragmentations. These tin(IV) enolates could engage in aldol
condensation and alkylation reactions. Chapter 4 also examines the
allyltributyltin-induced cyclopropyl ketone fragmentation-allylation.
The viability of free radicals as powerful synthetic intermediates has been
well proved.5 Free radicals are generated under mild and neutral conditions,
tolerate a wide range of functionalities, and usually react regioselectively and
stereoselectively. 0-stannyl ketyl radicals possess unique attributes in organic
synthesis. The work described in this dissertation broadens the knowledge of
this special ketyl species. 0-stannyl ketyl-promoted cyclopropane fragmen-
tation produces a free radical along with a regiospecific tin(IV) enolate. This
work individually manipulates these two intermediates. Further efforts to take
advantage of them both will definitely lead to exciting developments.












CHAPTER 2
STUDIES OF THE 0-STANNYL KETYL-PROMOTED
CYCLOPROPANE FRAGMENTATIONS


The origin of this work was the mechanistic studies of the 0-stannyl ketyl-
promoted cyclopropane fragmentations in the early 1970s by Godet and
Pereyre.25a,b,c They found that under free radical conditions, the reaction of
cyclopropyl ketone 130 with TBTH gave cyclopropane scission product 134, as
shown in Scheme 2-1. In this reaction, the carbonyl was first reduced to 0-
stannyl ketyl 131, which cleaved the adjacent cyclopropane. Radical product
132 was reduced by hydrogen abstraction from TBTH, giving tin(IV) enolate
133 and reproducing tributyltin radical to carry on the chain process. Enolate
133 was finally hydrolyzed to 134. This fragmentation mechanism was
confirmed later by other independent studies.25-27


0 OSnBu3 OSnBu3
&L TBTH -- R TBTH _
R AIBN R Bu3Sn
130 131 132
OSnBu3 0
H ,I ROH
R 0041 R
133 134

Scheme 2-1


0-stannyl ketyl-promoted cyclopropane fragmentations are synthetically
valuable. At the expense of a cyclopropyl ketone, an alkyl radical and a tin(IV)







enolate are produced. Although the original investigators did not explore either,

both the radical and tin(IV) enolate are useful intermediates in organic
synthesis. Cyclopropyl ketone 130 can be readily prepared by a variety of
methods, such as using an a,p3-unsaturated ketone and sulfur ylide,45 or

cyclopropanating an allylic alcohol and then oxidizing the product,46 or
cyclopropanating an alkene with a diazo function and a transition metal catalyst
intramolecularly or intermolecularly.47
The synthetic applications of the 0-stannyl ketyl-promoted cyclopropane
fragmentations had not been known prior to the work described in this
dissertation. Inspired by Motherwell's free radical cyclopropane fragmentation-
cyclization tandem sequence (Scheme 1-15),22 we planned to examine this
sequence promoted by 0-stannyl ketyl.





0 0
135 136


MeO 0 H


137 138

Figure 2-1
The simple cyclopropyl ketones for the fragmentation studies


To initiate our investigation of the 0-stannyl ketyl-promoted cyclopropane
fragmentations, four simple cyclopropyl ketones, shown in Figure 2-1, were
planned. The preparation of substrates 135 and 136 was first planned as that
shown in Scheme 2-2, starting from commercial aldehydes 139 and 140.
Addition of vinyl Grignard to the aldehydes gave allylic alcohols 141 and 142







in quantitative yields. Swern reaction was used to oxidize the alcohols to vinyl
ketones 143 (52%) and 144 (52%).48 Sulfur ylide method was employed to
produce cyclopropyl ketones 135 (18%) and 136 (24%) in modest yields.45


0

R, H


Vm

THF


139 R= Cg9H19g

140 R= C5H


rBr OH Swe
= L ., Swem (


100%141 R= C9H19

100%142 R= C5H1-


o -I~1o o

R -- NaH, DMSO R
52%143 R= C9H19 18% 135R= C9H19

52% 144 R= C5Hly\ 24% 136R=C5H11 /I


Scheme 2-2


OH

Rul-
141 R= CgH19 PI
142 R= C51-1

OH


141


OCO2Me

2(PPh3)4
hMe, A


0


83% 143 R= CgH19
69% 144 R=-C1 1 /


MnO2
CH2Cl2 or CHCI3, reflux


Scheme 2-3


oxidation
ON


no reaction







To improve the yields, a ruthenium-catalyzed oxidation method with allyl
methyl carbonate was used,49 affording vinyl ketones 143 (83%) and 144
(69%), as shown in Scheme 2-3. MnO2 oxidation was attempted as well.50
However, no oxidation was observed, even when the reaction mixture in
chloroform was refluxed.
The preparation of cyclopropyl ketones 135 and 136 was also achieved
by an alternative route shown in Scheme 2-4. The Grignard reagent of
cyclopropyl bromide reacted with aldehydes 139 and 140, providing
cyclopropyl alcohols 145 (76%) and 146 (70%). Pyridinium chlorochromate
(PCC) oxidized them to desired substrates 135 (83%) and 136 (78%).


0 [>-MgBr OH

R)H THF R"N<]
139 R= 09H19 76% 145 R= C9H19
140 R= C5H11 70%146R= C5H11 \/
0
PCC_- ,

CH2Cl2
83% 135R= C9H19
78% 136 R= C5Hl /

Scheme 2-4


Cyclopropyl ketone 137 was commercially available. The preparation of
substrate 138 was accomplished in quantitative yield from trans-chalcone 147
with sulfur ylide,45 as shown in Scheme 2-5.
The 0-stannyl ketyl-promoted cyclopropane fragmentations of these
simple substrates occurred readily in refluxing benzene, giving cyclopropane-
scission products in good yields, as shown in Scheme 2-6.








0 -Io G
j -S=OI 1 0

SI NaH, DMSO ,H
100%
147 138
Scheme 2-5


////TBTH, AIBN .%^
PhH, reflux
135 80% 148 O

/^^ TBTH, AIBN /
PhH, reflux
136 0 80% 149 0
MeO / \ TBTH, AIBN MeO / \
PhH, reflux
92%
137 150

H TBTH, AIBN
H'y PhH, reflux
86%
138 151
Scheme 2-6


For phenyl-substituted cyclopropane 138, its two CxCI3 cyclopropane
bonds (bond a and bond b) were not identical. When this cyclopropane
fragmented, two products 152a and 152b could form, as shown in Scheme 2-
7. Secondary radical 152b is strongly stabilized by a phenyl substituent and is
therefore much more stable than primary radical 151a. Because the
cyclopropane rotated freely, bonds a and b had the same orbital overlap with








the sp2-like orbital of ketyl radical 152. Thus, stereoelectronic influences were

absent in this fragmentation.51 As a result, this fragmentation was controlled by

radical-stability effects, selectively yielding 151.


138


152b


Scheme 2-7


LUMO- .
I
i I
i t
t t



SOMO

R H ROR

Hbon H an3

bond a OSnBu3


I %
I t
.. )-, LUMO


SOMO'-f-'



cD H> OSnBua bond b


Figure 2-2
SOMO-LUMO interactions of 0-stannyl ketyl with cyclopropane in 152



A second way to understand the cyclopropane fragmentation of ketyl

152 was through Mariano's FMO theory.12,25k A favorable interaction between

the SOMO of 0-stannyl ketyl (bearing electron-donating OSnBu3) and the







LUMO of a cyclopropane a-bond is required for its cleavage to occur. A
cyclopropane a-bond substituted with an EWG has a lower energy LUMO,
whereas that substituted with an EDG has a higher energy LUMO. For
cyclopropane 152, bond b carried EWG phenyl and had a lower LUMO than
bond a. Since stereoelectronic influences were absent, a better interaction was
achieved between the ketyl's SOMO and b's LUMO, as shown in Figure 2-2.
Thus, b cleavage was favored in this freely-rotating cyclopropane substrate.
To study the 0-stannyl ketyl-promoted fragmentation of a cyclopropane
fused in bicyclic or tricyclic systems, three such substrates (153, 154 and 155)
were planned, as shown in Figure 2-3.

0 0 0

>a a H
k O 2Me
Ph Ph
153 154 155
Figure 2-3
The bicyclic and tricyclic substrates


1) SOC12
2) P, Br2 LI quinoline
CO2H 3) MeOH t lBC02Me 990 a
89% Br C M 0 e
156 157 158

0 0
F S=u I-3
CrO3 I -
Ac2 I NaH, DMSO
AC20 6)eC02Mez~ 9%* J


51% CO2Me 35% CO2Me
159 153


Scheme 2-8







The preparation of 153 is shown in Scheme 2-8. The synthetic route to
159 followed Lange's procedure.52 Conversion of 156 to 157 was achieved
in 89% yield by HelI-Volhard-Zelinsky reaction. Dehydrobromination of 157 in
quinoline gave 158 in quantitative yield. Allylic oxidation with chromium(VI)
trioxide produced 159 in 51% yield. Sulfur ylide reaction transformed 159 to
153 in 35% yield.45
Substrates 154 and 155 were prepared from commercial a,p3-unsatu-
rated ketones 160 and 161 using sulfur ylides,45 as shown in Scheme 2-9.

h[ p --=O Ie
II ..
NaH, DMSO >
Ph Ph 81% Ph Ph
160 154
0~ 1 E)ol

NaH, DMSO Me
Me 1000/%
161 155
Scheme 2-9

Bicyclic and tricyclic substrates 153,154 and 155 possess a rigidly
fused cyclopropane. Stereoelectronic requirements of orbital overlap are
expected to govern these cyclopropane fragmentations. For each substrate,
once 0-stannyl ketyl forms, its sp2-like orbital has better overlap with bond a.
Bond b, conversely, is almost orthogonal to this sp2-like orbital, as illustrated in
Scheme 2-10.53,54







OSnBu3

a OSnBU1 S 162a
/-/\^ ^^MeOC
a.b OSnBU
Me MeC2C
~OSnBu3
162 b /f 1 162b
MeO2C
OSnBu3

a OSnBu3a P 163a
SPh H
Ph Ph OSnBu3
Ph b 0 163b
163 Ph
H
Ill
Ph
j/ OSnBu3
,,1OSnBu3 a 164a


$ a^ OSnBu3
164 b W
6164b


Scheme 2-10


On the basis of stereoelectronic effects,51 bond a cleavage should
predominate over bond b cleavage, and the a cleavage products (162a, 163a
and 164a) should predominate in the fragmentations. For 0-stannyl ketyl 162,
stereoelectronic effects compete with radical-stability effects which favor bond b
cleavage, due to the stabilization of 162b by the ester. Intermediate 162a may
form kinetically, but the more stable ring-enlarged 162b would eventually







predominate in the equilibrium, because of the reversibility of cyclopropane
fragmentation.55 Thus, ring expansion could occur for substrate 153 under
treatment of TBTH and AIBN.

0 OSnBu3 0
JTBTH, AIBN
|PhH, reflux"1
CO2Me 69%
CO2Me CO2Me
153 162b 165
0 OSnBu3 0

TBTH, AIBN N.
> PhH, reflux
86% Me
Ph Ph Ph Ph Ph Ph
154 163a 166

/ e0 0- OSnBu3 4, 0
H TBTH, AIBN Me PhH, reflux- Me Me
76% Me
155 164a 167
Scheme 2-11


To examine if stereoelectronic effects or radical-stability effects would
predominate in the cyclopropane fragmentations, the reactions of substrates
153,154 and 155 with TBTH and AIBN were performed. As shown in Scheme
2-11, for ester-substituted cyclopropane 153, ring expansion product 165
(69%) was exclusively yielded, revealing predominance of 162b in the
fragmentation. Radical-stability effects overcame stereoelectronic effects for this
substrate and bond b was selectively cleaved. For substrates 154 and 155,








bond a cleavage predominated and stereoelectronic effects-favored products
166 (86%) and 167 (76%) were yielded. Apparently, the driving force for more

stable bond b-scission products 163b and 164b was not sufficient enough to
compete with stereoelectronic effects. Thus, it was clear that the significance of
radical-stability effects mainly depended on the substitution pattern of the
cyclopropane. An ester or similar radical-stabilizing group at the cyclopropane's
CP position was required for radical-stability effects to predominate. Recently,

Cossy reached a similar conclusion by studying the photochemical electron
transfer-induced ring scission of cyclopropyl ketones.54
A unique cyclopropyl ketone, tricyclo[3.3.0.02,8]octan-3-one 168 (Figure
2-4), strongly held our attention and curiosity.35 Containing a geometrically
defined a-ketocyclopropane component rigidly fused on parent diquinane, 168

was perfect for examining the competition of stereoelectronic effects and

radical-stability effects in 0-stannyl ketyl-promoted cyclopropane scissions.
Stereomodels of 168 showed that the n-bond of the carbonyl forms a dihedral

angle of approximately 25 with the C2-C8 ,a-cyclopropane bond a.56 Bond a is
geometrically disposed for better overlap with the adjacent X-system than the

C1-C2 o-cyclopropane bond b.


2 a 8 0C 1
280
3 7 2 I
4 5 6 6

168 8 7

Figure 2-4
Tricyclo[3.3.O.02,8]octan-3-one







Metal-associated ketyl-mediated cyclopropane fragmentation of 168 was
investigated by Monti in 1969, using harsh lithium-liquid ammonia medium, as
shown in Scheme 2-12.56 Stereoelectronic effects governed this ring scission.
The overall two-electron reduction selectively cleaved bond a, giving 169 and
170 in a ratio of 20 to 1.




NHa(liquid)
U't j =(: + 0clz&
20:1
168 169 (20:1) 170
Scheme 2-12


The examination of this cyclopropane fragmentation using TBTH and
AIBN was planned. Prior to the work presented in this dissertation, it had not yet
been clear whether 0-stannyl ketyl would behave in an analogous manner.
This 0-stannyl ketyl-promoted fragmentation markedly differed from the lithium-
ammonia redox process in mechanism. 0-stannyl ketyl reacted by free radical
pathway under mild conditions, relative to the dissolved metal reduction.
The special merit of tricyclo[3.3.0.02,8]octan-3-one 168 in the synthesis
of cyclopentanoid natural products was recognized in 1980 by Demuth and
Schaffner.57 They predicted that this tricyclic ketone would provide "versatile
building blocks for the total synthesis of polycyclopentanoids and related
compounds".58 Since then, many natural compounds have been synthesized
using this ketone as a key intermediate,58-60 including (-)-coriolin,61 (-)-
silphiperfol-6-en-5-one,62 and ()-modhephene.63
The preparation of tricyclo[3.3.0.02,8]octan-3-one 168 has been
achieved by different routes, including metal carbene insertion reactions.56,64







The route via oxa-di-ic-methane (ODPM) rearrangement of bicycle 171 is
apparently expeditious, as shown in Scheme 2-13.58 This rearrangement is
easy to perform, by just simply irradiating the dilute solution of 171 in a triplet-
sensitizing solvent, such as acetone or acetophenone. This photochemical
rearrangement always gives very good yields. Racemic 171 could be readily
enantiomerically separated by protecting the carbonyl with diethyl (R,R)-tartrate,


R


171
(R=H, R, OR, CO2R)


hv
triplet-sensitizing
solvent
70-90%


168


Scheme 2-13


H
R



172

jODPM


H
0O2R



173

,ODPM


)2R
'02R


174

ODPM


H H RO2C



KL Co2R C
175 176 177
Figure 2-5
The tricyclo[3.3.0.02,8]octan-3-one substrates and
their ODPM rearrangement precursors


)2R







separating the ketal diastereomers by chromatography, and then deprotecting
the carbonyl through acidic hydrolysis.58,59 Each enantiomer can be thus
obtained in >98% e.e. (enantiomeric excess). This offers a synthetic approach
for enantiomerically pure cyclopentanoid natural products.
To study the 0-stannyl ketyl-promoted cyclopropane fragmentation in
tricyclo[3.3.O.02,8]octan-3-one substrates, three substrates (172,173 and 174)
were planned, as shown in Figure 2-5. Using these compounds, the
significance of radical-stability effects relative to stereoelectronic effects in the
fragmentations could be examined. So could the influence of the Cl- and C2-
substituents to the reactions.


0 1) LDA, THF, -78C
2) -= CO2Et NCO2Et
0==K

178 179

0 1) LDA, THF, -780C
S2) =C -C02Et(180) C02Et


178 181

Scheme 2-14


To synthesize the analogs of 176, well-documented double Michael
addition was initially used.65 Unfortunately, the starting molecules extensively
polymerized (Scheme 2-14). Ethyl allenecarboxylate 180 was prepared
according to Lang's procedure, as shown in Scheme 2-15.66 Its low yield was
due to the difficulty in removal of a large amount of solid Ph3PO byproduct
before distillation. These double Michael approaches were abandoned.








0
Br..LJ
1Br8OEt

182


Ph3P
PhH Ph;
99%


1) Et3N (0.5 eq), CH2Cl2
2) CH3COCI (0.5 eq), CH2Cl2
3) distillation, 17%


OEt


183


CO2Et


180


Scheme 2-15


Diels-Alder cycloaddition was chosen to synthesize 176 and 177, using
trimethylsilyloxycyclodiene 185 and mono- or double-ester-activated acetylene
as dienenophile.67 Diene 185 was prepared in 87% yield from cyclohexenone
178 by Rubottom's method, as shown in Scheme 2-16.68


0

[ LDA
STHF
-78C
178


0 G
Li 0 OTMS

TMSCI O
87%/

184 185
Scheme 2-16


The Diels-Alder reaction of 185 and dimethyl acetylenedicarboxylate
(DMAD) 186 was carried out in refluxing toluene at 120C. However, instead of
bicyclic adduct 177, phenol 189 was obtained in 89% yield, as shown in
Scheme 2-17. The formation of this phenol was rationalized with a retro Diels-
Alder process occurring at the relatively high reaction temperature, through
which ethylene was liberated. Aromaticity was the obvious driving force.







Similarly, the reaction of 185 with ethyl propiolate 190 in refluxing toluene
produced phenol 191 in 95% yield, instead of desired bicycle 176.


OTMS CO2Me
PhMe
+ I1200
CO2Me 89%
185 186


,CO2Me


187


TMS1
H2C=CH2
retro Diels-Alder


.CO2Me H
H30+
'CO2Me


188


OTMS



185
185


H

+ II
CO2Et
190


189


1) PhMe, reflux HOya
2) H30+ l
95% C02Et
191


Scheme 2-17


In order to prevent the retro Diels-Alder process, the reaction of 185 and
DMAD 186 was performed at a lower temperature (80C in benzene). The
Diels-Alder reaction worked very well, giving desired cycloadduct 177 in 61%
yield, as shown in Scheme 2-18. Phenol 189 was still produced, but only as a
minor product this time.
The reaction of 185 and 190 was carried out in refluxing benzene for 2
days. Adduct 176 was isolated in 35% yield, with retro-[4+2] product 191 as the
major product. This cycloaddition then was performed in a sealed flask at 70-







75C. After 7 days, 176 was afforded in 88% yield, with a small amount of
phenol 191.


CO2Me MI
II 1)PhH,800C
+ 2) H30+ 0
CO2Me 61%
186
H
III 1) PhH, 70-750C
+ 2) H30+
CO2Et 88%
190


eO2C
OCO2Me


177
H

0 ='\C(02E


OTMS


0
185
OTMS



185


Scheme 2-18

To improve the yields, these Diels-Alder reactions were attempted at still
lower temperatures (0C-60C). Disappointingly, the reactions were too slow to
be useful and the retro-[4+2] process still could not be completely suppressed.
An effort to catalyze the cycloaddition with Lewis acid SnCl4 at -78C was also
unsuccessful.


171


hv
1,3-acyl shift
192

hv, triplet sensitizer 0raa O
ODPM rearr.
168


Scheme 2-19


176







With precursors 176 and 177 in hand, it was time to examine the ODPM
rearrangement.69 This bicyclo[2.2.2]octenone photorearrangement was first
investigated by Givens in 1971.70 As shown in Scheme 2-19, direct
photochemical irradiation of bicyclo[2.2.2]octenone 171 afforded 1,3-acyl shift
product 192, while triplet-sensitized irradiation gave ODPM rearrangement
product 168.58,59



0 hS0J- 0h
0=<) S J~=aJX^s =
171 193 194
01 0'tIO



194 192

Scheme 2-20


The mechanism of these photochemical rearrangements have been well-
studied.58 The 1,3-acyl migration is initiated by photolytic a-cleavage of the
ketone to acyl-allyl diradical, which has the option of either regenerating the
starting material or recombining in the alternative allylic position and forming
1,3-shift product 192, as shown in Scheme 2-20. This reaction occurs from the
n,7r* singlet excited state S1 (n,7r*) and also from the triplet excited state T2(n,n*),
as indicated in Figure 2-6.
ODPM rearrangement occurs from the lowest lying excited triplet state
Ti (n,lr*).58 ETsens represents the excited-state energy of the selected triplet
sensitizer. After the triplet sensitizer reaches its excited state by absorbing the





















Figure 2-6
Energy diagram of bicyclo[2.2.2]octenone 171


o hv
triplet
171 sensitizer





197


195 196




197 168

Scheme 2-21


irradiation energy hv, the sensitizer delivers and unloads energy ETsens to

bicyclo[2.2.2]octenone 171. If the energies of T1i, T2 and ETsens have been

carefully adjusted by choosing the right triplet sensitizer and optimizing the
irradiation wavelength and enone concentration, the ETsens can be set exactly
between T2 and T1i. In this case, energy ETsens is exclusively transferred from
the sensitizer to bicyclo[2.2.2]octenone's T1 to secure ODPM rearrangement to
occur.58 TI-excited enone 171 can be expressed by diradical 195, as shown

in Scheme 2-21. The carbon-centered radical adds onto the alkene to form


1,3-acyl
shift


ETsens


1,3-acyl
shift

ODPM
rearr.







cyclopropane-separated diradical 196. The oxygen-centered radical cleaves

the cyclopropane to give 197, where coupling of the two carbon-centered
radicals yields tricyclic ketone 168. This photochemical sequence is termed
"oxa-di-ic-methane" or "ODPM" rearrangement.58

The two best reaction conditions for an efficient ODPM rearrangement
have been reported to be: 1) acetone as the sensitizer and solvent, enone
concentration less than 2%, ,irr =300nm; 2) acetophenone as the sensitizer,

pure acetophenone or 20% acetophenone in acetone, benzene or cyclohexene
as the solvent, enone concentration less than 10%, Xirr >340nm.59 The

advantage in acetone serving as sensitizer is the ease in workup and isolation
of the product, due to the low boiling point (56C) of acetone. However, the
enone concentration should not exceed 2% in acetone; otherwise the direct
energy absorbance of the enone will become noticeably competitive, giving 1,3-
acyl shift byproduct 192. When acetophenone serves as sensitizer at >340nm,
the direct enone absorbance is negligible, and the enone concentration can be
as high as 10%. The negative side of acetophenone is the difficult removal of
this compound (boiling point 202C), after the rearrangement is complete.

A 450W Hanovia medium-pressure mercury-vapor lamp was used to
irradiate the ODPM rearrangement precursors. In order to match the literature
wavelength mentioned above, the irradiation was conditioned with a Pyrex
glass filter. Pyrex glass is capable of absorbing most of the <320nm irradiation.
To compare the efficiency of acetone and acetophenone as sensitizer,
ODPM rearrangement was performed using a 0.08M solution of 177, as shown
in Scheme 2-22. When acetone was used, the photorearrangement was
complete in 24 hours, smoothly affording 174 in 83% yield. When
acetophenone was the solvent and sensitizer, the reaction finished in 12 hours.
After most acetophenone was distilled away, the residue was chromatographed








to separate the remaining acetophenone and rearrangement product. Tricyclic
174 was isolated in 92% yield. Obviously, acetophenone was a more efficient

sensitizer for ODPM rearrangement, giving higher yield in shorter irradiation
time. However, due to the tedious acetophenone separation, acetone was

preferred as our triplet sensitizer.


Me02C
CO2Me



177


CO2Me
ICO2Me


hv, Pyrex filter
No
triplet sensitizer
0.08M


174


sensitizer & solvent
acetone
acetophenone


irradiation time
24hrs
12 hrs


isolated yield
83%
92%


Scheme 2-22


H
OCO2Et



176


hv, Pyrex filter
acetone, 0.08M
88%


Scheme 2-23


The ODPM rearrangement of 176 was accomplished in 84% yield after
24-hour irradiation in acetone, giving tricyclic substrate 173. The yield was
improved to 88% when 176 was irradiated for 48 hours, as shown in Scheme

2-23.
The preparation of Cl-alkyl-substituted substrate 172 (Figure 2-5)
started directly from 173, as shown in Scheme 2-24. Tricycle 173 was reduced


173







using excess amount of diisobutylaluminum hydride (DIBAH, 5 equivalents) to
diol 198 in 99% yield. The primary hydroxy group was selectively protected
with 1.2 equivalent of t-butyldiphenylsilyl chloride (TBDPSCI). Oxidation of
secondary alcohol 199 to ketone 172 was done with PCC in 70% yield.
Bearing t-butyldiphenylsiloxymethyl at its Cl position, compound 172 was
suitable for studying the influence of CI-alkyl on the 0-stannyl ketyl-promoted
tricyclo[3.3.0.02,8]octan-3-one fragmentation. Thus, substrates 170,171 and
172 planned in Figure 2-5 were all synthesized.

H H OH
ICOB Et
0 DIBAH (excess) HO TBDPSCI (1.2eq)
CH2Cl2, -780C pyridine, 0C
99% 37%
173 198
H OTBDPS H OTBDPS

HO PCC -0
\CH2Cl2, r.t.
L70%
199 172
Scheme 2-24

Bu3SnO
2 a 8 ^

Bu3SnOb 2


200 8
Figure 2-7
0-stannyl ketyl of tricyclo[3.3.0.02,8]octan-3-one








For tricyclo[3.3.O.02,8]octan-3-one substrates, once 0-stannyl ketyl 200
forms, bond a (C2-C8) has better overlap with the ketyl's sp2-like orbital than
bond b (Cl -C2) does, as shown in Figure 2-7. Thus, stereoelectronic effects
favor bond a cleavage in the fragmentation.35
The reactions of tricyclic substrates 172,173 and 174 with TBTH and
AIBN in refluxing benzene are shown in Scheme 2-25.35 Tricyclic 172
(RC1=alkyl) afforded bond a cleavage product 202 in 83% yield in 4 hours.
Ester 173 (RCl=ester) gave a single diastereomer 204 in 88% yield in 1 hour.

When the reaction time was extended to 5 hours, the yield was improved to
94%. Interestingly, diester substrate 174 (RCi =RC2=ester) produced only bond

a cleavage product 206 in 59% yield, though its Cl-ester function was capable
of stabilizing the radical formed by bond b cleavage. It was contradictory that
174's Cl-ester did not play a role in the cyclopropane fragmentation, while
173's Cl-ester apparently overwhelmed stereoelectronic effects.35 Substrates
173 and 174 differed only by the presence of an additional ester group at the

C2 position of 174.
Unequivocal confirmation of the product structures shown in Scheme 2-
25 was required. Structure 204 had C2 symmetry, possessing 3 pairs of

identical carbon atoms. Its 13C NMR (nuclear magnetic resonance) spectrum
clearly supported this C2 symmetrical structure. Only 8 carbon peaks were

recorded in the spectrum. Obviously, the 3 pairs of carbon atoms only gave 3
single peaks due to the identical chemical shift of the two individual carbon
atoms in each pair. To desymmetrize 204 and observe all the carbon peaks, it
was converted to 2,4-dinitrophenylhydrazone derivative 207, as shown in
Scheme 2-26. Now there were three additional carbon peaks appearing in the
NMR spectrum. Thus, the symmetrical structure of 204 was confirmed.







S OTBDPS, un .OTBDPS OTBDPS
TBTH
O^N S AB N Bu3SnO^^V / "^
AIBN__0 I
172 201 202
H
Et ~ H HCO0Et
(C~Et iECgt "^O2Et
F02 TBTH _J-t t
0 AIBN Bu3SnO /.
88% 0
173 203 204
CO2Me CO2Me CO2Me
,_2M MTBTH I MO2Me e
0* 7 AIBN Bu3SnO /j O=
0 L 59%
174 205 206
Scheme 2-25


NO2 H C02Et
H CO2Et / \
H2N ON NHNH2 N02
MeOH, H2SO4 02N N I
S 204 55% H/ H 207

Scheme 2-26

The structural assignment of 204 was determined on the basis of proton
NMR analysis and comparison with the spectra of known structurally-similar
compounds 208L and 208R reported by Yates and Stevens.71 The two
possible structures of 204 are given in Figure 2-8: 204L and 204R. Inspection
of a molecular model of 204L showed that the dihedral angle between C1-H or










5 6
\HscO2Me


HO 1 7
CO2Me
208L
C8-H: 8 2.86, singlet


H 8 CO2Et EtO2 8H
HH

) 2 5 7^ 6 2 1 5 7 6
0 3 4 H 0 3 4 H
204L 204R
C8-H: 8 2.77, singlet


MeO2C


HO03- 1 H 7
CO2Me
208R
C8-H: 8 2.67, triplet, J=4Hz

CO2Et



Bu3SnO / HI
H H
H H
203


Figure 2-8
The structural assignment of 204


C5-H and C8-H bonds was about 90, which would result in negligible coupling
between the C8-H and the Cl/C5-H.71,72 A molecular model of 204R showed
that the corresponding dihedral angle was 45, which would result in the
splitting of the C8-H signal into a triplet with coupling constant J of about 4
Hz.71,72 The observed 204's C8-H resonance was a singlet at 2.77 ppm. This
signal was in nice agreement with that of structurally-similar 208L (singlet at
2.86 ppm). This indicated that 2041L was the single diastereomer produced in
the cyclopropane fragmentation of 173.
Thus, excellent stereoselectivity in the hydrogen abstraction from TBTH
was achieved for radical intermediate 203 (Figure 2-8). TBTH could approach
the C8 radical site from the L face or the R face. Due to the presence of flat
tin(IV) enolate, the L face was much more sterically open than the R face.
Therefore, TBTH selectively approached from the L face to afford 204L.







To confirm the presence of radical intermediate 203 in the cyclopropane
fragmentation, the reaction of 173 and tributyltin deuteride (TBTD) was
performed to trap out this intermediate by deuterium abstraction, as shown in
Scheme 2-27. Symmetrical 204D was isolated in 78% yield. Comparison of the
1 H and 13C NMR spectra of 240D and 240 indicated that the deuteration
occurred at C8 position of 240D. Key intermediate 203 was thus confirmed.

HCO2Et mgmo HCO2Et D C( Et
TBTD H U~ ~OE
0 ABN BuSnO TBTD /
PhH, reflux T BT
3 days, 78% 0
173 203 204D

Scheme 2-27

H
t TBTH (1 Oeq) H Y
0 AIBN (5eq) Bu3SnO /-E CN
y PhH, reflux
173 1 hr,99% 203
173 203

CO2Et C02Et
NC NCN
RO H A O E
Bu3SnO 0 O
209 210
Scheme 2-28

Surprisingly, when excess amount of AIBN was used in the reaction of
173 and TBTH, nitrile 210 was obtained in quantitative yield, as shown in
Scheme 2-28. This nitrile arose from the coupling reaction of intermediate 203







with cyanoisopropyl radical, formed in thermal decomposition of AIBN (Scheme
1-1). It was interesting that 203 coupled faster with cyanoisopropyl radical than
abstracting a hydrogen from TBTH. The formation of 210 also confirmed
presence of 203. The participation of cyanoisopropyl radical in free radical
reactions is known in literature.14b


CO2Me CO2Me
CO2Me CO2Me
0HO 0 NaBH4
MeOH-
-78C, 2 hrs
206 206T
CO2Me
CO2Me
MsCI M O-d DBU
Et3N, CH2Cl s THF
-20C, 3 hrs 70C
212


CO2Me
I CO2Me


211


CO2Me



213e
213


Scheme 2-29


The structure of cyclopropane-opening product 206 needed to be
confirmed. The spectroscopic evidence was not conclusive for this structure,
because the diester ketone product was complicated by an equilibrium mixture
with its tautomer 206T. Both were clearly visible on the NMR time scale. To
conclusively confirm the structure, the C3-carbonyl was removed using a three-
step sequence illustrated in Scheme 2-29. The 206/206T mixture was reduced
to alcohol 211 with sodium borohydride at -78C. The alcohol was activated
using mesyl chloride at -20C. Elimination of 212 with 1,8-diaza-
bicyclo[5.4.0]undec-7-ene (DBU) in refluxing THF afforded 213 as the sole
isolable product. The 13C NMR and the attached proton test (APT) study for
213 revealed presence of 4 quaternary carbons (176.6, 164.6, 137.6, 65.7







ppm), 2 CH units (144.8, 49.4 ppm), 4 CH2 units (39.7, 35.6, 35.4, 26.1 ppm)
and 2 CH3 units (52.2, 51.5 ppm) in this compound. These NMR data
conclusively confirmed the assigned structure of 213.35

R2

BuaSnO >T/>
R2 R2 BU3SnJ
1 lia //a cleavage 215a
B u3Sn" Bu3SnO
JLb cleavage R
214 215 IR,
Bu3SnO /j7j


215b
Scheme 2-30


To explain the contrasting cyclopropane fragmentation results from very
similar structures in Scheme 2-25, it was proposed that stereoelectronic effects
initially favored the cleavage of bond a in all three precursors (172, 173 and
174), and 215a initially formed in each case, as shown in Scheme 2-30.35 It
was proposed that a reverse reclosure also involved, though cyclopropane
scission occurred at a much higher rate to release ring strain. If R2=H, as in 172
and 173, the reclosure was more facile, because no substituent was present at
C2 to sterically hinder this center. At this point, cleavage of bond b was likely to
occur if there was a sufficient driving force. For 173 (RI=CO2Et), the driving
force of radical-stability effects was significant enough to cleave bond b,
because its Cl-ester could much stabilize radical 215b (i.e. 203). Once this







radical was stabilized, the reverse reclosure was energetically unfavorable and
less likely. Radical 203 thus remained until hydrogen abstraction from TBTH
occurred to give 204.
Substrate 172 (RI=CH2OTBDPS) lacked radical-stabilizing substituent

at its Cl position. Though the a cleavage was reversible, there was no driving
force for the cyclopropane scission to proceed by the stereoelectronically-
unfavored bond b cleavage pathway. Thus, radical 215a (i.e. 201) underwent
hydrogen abstraction from TBTH, yielding 202 after hydrolysis.
Diester substrate 174 (RI=R2=CO2Me) was different. After the
stereoelectronically-favored bond a cleavage occurred initially, the R2-ester

group sterically blocked the reclosure of radical 215a (i.e. 205) to 215. Similar
rate-retarding effects by blocking 5-hexenyl radical cyclization at the internal C5

position of the alkene have been well-established.1 But they are not yet well-
understood for 3-butenyl radical cyclizations. It is further noteworthy that if
R2=CO2Me, as in the case of 174, the reclosure prevents conjugation of the

ester with the olefin, which is also energetically less favorable. Thus, 205 was
the cyclopropane fragmentation product, giving 206 after hydrogen abstraction
from TBTH and hydrolysis.
In conclusion, the 0-stannyl ketyl-promoted cyclopropane fragmentations
were studied using various substrates: simple cyclopropanes, cyclopropanes
fused on other rings, and tricyclo[3.3.O.02,8]octan-3-ones. These ketyl-mediated
fragmentations are governed by both stereoelectronic effects and radical-
stability effects. The significance of the latter effects depends on the substitution
pattern of the cyclopropane. These studies enable us to apply the cyclopropane
fragmentations to organic synthesis, which is the subject of next chapter.













CHAPTER 3
APPLICATIONS OF THE 0-STANNYL KETYL-PROMOTED
CYCLOPROPANE FRAGMENTATIONS TO THE
SYNTHESIS OF TRIQUINANE COMPOUNDS


New methods for the construction of condensed cyclopentanoid ring
systems (polyquinanes) continue to be developed at an accelerated pace since
the 1970s.60 Among important naturally occurring polyquinanes are tricyclic
polyquinane sesquiterpenes, which are termed "triquinanes" and can be
classified as linear, angular or propellane according to ring fusion (Figure 3-
1).73a Triquinanes come from a wide variety of natural sources and many

possess significant antibiotic and/or antitumor activity.73a These structurally
interesting triquinane natural products provide a particular vehicle for the

application of various new cyclopentanoid synthetic methodologies.60







linear angular propellane

Figure 3-1
The skeletons of triquinane compounds


There are more than 40 different triquinane terpenes found in the
nature.74 Figure 3-2 shows the structures of several natural triquinanes. Among
them, linear triquinane capnellene (216), hirsutic acid (217) and coriolin (218)
have three cyclopentane rings linearly cis,anti,cis fused in a straight chain.







Angular triquinane subergorgic acid (219) and isocomene (220) possess three
cyclopentane rings cis,anticis fused in an angled array. Modhephene (221) is
a propellane triquinane.

HH 0
H H H ..
H O2C%* H1 "H

OH
capnellene (216) hirsutic acid (217) coriolin (218)
0 H
". | H H".,1
H 02C /. H


subergorgic acid (219) isocomene (220) modhephene (221)

Figure 3-2
Several natural triquinane compounds

The field of triquinane synthesis has greatly expanded since hirsutic acid
216 was first synthesized in 1974 by Matsumoto.75 Numerous synthetic routes
were attempted, and every major naturally occurring triquinane has been
successfully prepared in organic labs.60,74 Many triquinanes have even
several syntheses using a variety of approaches, such as the compounds listed
in Figure 3-2.
Among the powerful approaches for triquinane synthesis is a free radical
tandem cyclization sequence to construct two new cyclopentanes fused on the
parent cyclopentanoid substrate in a single transformation. This synthetic route
was elaborated by Curran and coworkers.73 In this route, a bromide or iodide







must be properly placed in the cyclization precursor. With treatment of TBTH
and AIBN, this bromide or iodide produces a reactive free radical (222 and
225), which cyclizes onto a cyclopentene to form a bicyclic diquinane radical
(223 and 226), as shown in Scheme 3-1.73e This new radical then cyclizes
onto a tethered olefin or alkyne to produce a linear (224) or angular (227)
triquinane skeleton. One such example is Curran's synthesis of hirsutene 229,
as shown in Scheme 3-2.73a,b For this linear triquinane synthesis, the trans
stereochemistry of the two tethers in radical reaction precursor 228 is essential
for accomplishment of the naturally-occurring cis,anti,cis ring fusion in the
tandem cyclization sequence.




( "'~*linear
(S..- (C^C^
S\,." triquin.
222 223 224


__ ,angular
triquin.

225 226 227

Scheme 3-1

H
H
TBTH
AIBN
64% H
228 229


Scheme 3-2







One main drawback of Curran's approach is that too many steps are
usually required to prepare the tandem cyclization precursor. For example, a
12-step synthesis was used to synthesize precursor 228 in Curran's route for
hirsutene 229.73a,b All these steps were directed to setup the combination of a
multiple-bond tether and a diquinane radical (223 or 226).
Chapter 2 has reported our studies on the 0-stannyl ketyl-promoted
cyclopropane fragmentations. The fragmentation of tricyclo[3.3.0.02,8]octan-3-
one substrates selectively gives the bond a (C2-C8) cleavage product, unless a
radical-stabilizing substituent is at the Cl position. As shown in Scheme 2-25,
the cyclopropane fragmentations of 172 and 174 produced diquinane radicals
201 and 205, which could be utilized to achieve triquinane synthesis.
To thus accomplish triquinane synthesis on the basis of our previous
studies, a novel 0-stannyl ketyl-promoted cyclopropane fragmentation-
cyclization tandem sequence was envisioned. As illustrated in Scheme 3-3, if


I I
2 8
0* 7 TBTH Bu3SnO *
^u ~AIBN v
230 231


Bu3SnO / Bu3SnO '


232 233
Scheme 3-3


an olefin or alkyne tether was placed at C7 (230), after the cyclopropane
fragmentation, the cyclization of diquinane radical 232 would yield linear







triquinane 233. If the tether was placed at Cl (234), the radical cyclization
would produce angular triquinane skeleton 237 (Scheme 3-4). This work would
generate a new general approach towards the synthesis of triquinane
compounds by taking advantage of tricyclo[3.3.O.02,8]octan-3-ones. Compared
to Curran's general route, this approach could reach the final triquinane
cyclization stage in a shorter and more efficient manner. Much of this simplicity
could be found in the use of a ketone (230 or 234) to initiate the radical
process, rather than a halide.




O S 28TBTH Bu3SnO
Y7 Do SJ-
AIBN
234 235


Bu3SnO / Bu3SnO._ .


236 237

Scheme 3-4


H

040
OOH

H
238 239
Figure 3-3
The model precursors for cyclopropane fragmentation-
cyclization sequence and triquinane skeleton synthesis







To examine this 0-stannyl ketyl-promoted cyclopropane fragmentation-
cyclization tandem sequence and demonstrate this new triquinane synthesis
approach shown in Schemes 3-3 and 3-4, two model precursors 238 and 239
were planned, as exhibited in Figure 3-3.36,37 Note that they differ primarily by
placement of the olefin tether.
To synthesize precursor 239 from 1-ethoxycarbonyltricyclo[3.3.0.02,8]-
octan-3-one 173, which had been prepared in chapter 2, the route shown in
Scheme 3-5 was initially planned. Tricycle 173 was reduced to diol 198 with
excess DIBAH. Oxidization to dicarbonyl 240 with PCC was achieved in 52%
yield for these two steps. To finish the preparation of 239, it was attempted to
take advantage of the reactivity difference between a ketone and a presumably


CO2Et OH
O* ,- DIBAH (5 eq)HOA \PCC
-' T CH2Cl2 CH2Cl2
-780C-r.t. 52% from 173
173 198

CHO MgBr HO/
/OM'B (1 .1 eq
THF, -78C F
240 239

Scheme 3-5


more reactive aldehyde by treatment with 1 equivalent of allyl Grignard reagent.
Disappointingly, the reactivity difference between the ketone and aldehyde
carbonyls in 240 was negligible and the selectivity in this addition was very
poor. Even when 1.1 equivalent of allylmagnesium bromide was added
dropwise to a very dilute 240 solution (0.1 M) at -78C, double-Grignard-







addition product was still obtained along with remaining unreacted 240. In
order to add an allyl unit to the aldehyde, the ketone had to be protected before
the Grignard reaction. Thus, our synthetic approach was modified to that shown
in Scheme 3-6.36

CO2Et HO A C02Et
o^/^ \ 4 H o0>F DIBAH (2.1 eq)
PPTS (cat.) 0 CH2Cl2, -78C
PhH, reflux 96%
173 Dean-Stark, 90% 241

O0 O H ..rCO C H O 1/ M gB r 0 H
SCH2CI2 0 M2) H30 (1.3:)
67% 85%
242 243 239
Scheme 3-6


Protection of the ketone carbonyl of 173 using ethylene glycol and mild
catalyst PPTS (pyridinium p-toluenesulfonate) gave ketal 241, as shown in
Scheme 3-6. A Dean-Stark tube was attached to the reaction flask. This
protection was complete in 12 hours in 90% yield. To reduce the Cl-ester group


OH "OH OH
0 0EtDIBAH (4 eq) 0 7 DDAH CKI1h
CH2CI2, O 71% /
-78C-r.t.
241 242 244


Scheme 3-7







of 241, 4 equivalents of DIBAH were used in the first attempt. Interestingly, the
ketal protective group was reductively cleaved by the excess amount of DIBAH
remaining after the ester reduction had been complete, and diol 244 was
isolated in 71% yield (Scheme 3-7). Similar reductive cleavages of ketals and
acetals by hydride donors are known in literature.76
In next attempt, only 2.1 equivalents of DIBAH were added to 241 at
-78C, as shown in Scheme 3-6. Primary alcohol 242 was yielded in 96% yield,
and no overreduced product 244 was found. To oxidize 242 to 243, PCC was
initially used. However, during the oxidation, the ketal protection group was
cleaved. Dicarbonyl 240 was obtained as the major product in 67% yield, while
243 was isolated in a yield less than 5% (Scheme 3-8). This carbonyl
deprotection was rationalized by the acidity of the PCC reagent.


OH
0 PCC CHO r CHO

0 ~~CH2CI2a**nOt

242 240 (67%) 243 (<5%)

Scheme 3-8


To avoid the deprotection, a slightly basic oxidant pyridinium dichromate
(PDC) was used, oxidizing 242 smoothly to desired ketal aldehyde 243 in 67%
yield, as shown in Scheme 3-6. The allyl tether was added to the aldehyde
through a Grignard reaction. The ketal protective group was removed during the
normal Grignard acidic workup, giving precursor 239 in 85% yield. The GC
ratio of the two 239 diastereomers was 1.3 to 1. These two diastereomers were
not separable from each other by column chromatography.







Now it was time to examine the proposed 0-stannyl ketyl-promoted
cyclopropane fragmentation-cyclization sequence and angular triquinane
synthesis approach (Scheme 3-4). Refluxing 239 in benzene at a concentration
of 0.1 M for 14 hours, with 2 equivalents of TBTH and 1 equivalent of AIBN,
smoothly furnished angular triquinane 245 in 94% yield, as shown in Scheme
3-9. The GC ratio of the major cyclization products (the C11-diastereomers) and
the minor cyclization products was 57:1. The GC ratio of the 245 C11-
diastereomers was still 1.3:1.36


HO /1O 10 ,H

STBTH, AIBN 7,, ,I
^ 7 --- *" /3 8 \7
(1.3:1) PhH, reflux 5::y (1.3:1)
94% 4 6
239 245

Scheme 3-9


NMR was used to establish the stereochemistry of triquinane 245 at the
C9 center. Based on Whitesell's 13C NMR studies,77 if the C9-methyl was
endo, the C9 resonance should be around 15 ppm and the C8 resonance
should be around 33.0 ppm (for endo C 11-OH) and 35.4 ppm (for exo C11-OH).
If the C9-methyl was exo, the C9 resonance should be around 19 ppm and the
C8 resonance should be around 37.4 ppm (for endo C11-OH) and 39.8 ppm
(for exo C11-OH). The 13C NMR spectrum of 245 clearly indicated that for the
major cyclization products, the C9-methyls were at 14.5 and 14.6 ppm, and the
C8-tertiary centers appeared at 31.0 and 33.2 ppm. These characteristic 13C
NMR peaks were in excellent agreement with those calculated for the endo-C9-
methyl stereomers by Whitesell's method. Thus, the C9-methyl stereochemistry
of the major products 245 was established as endo.







Excellent stereochemical control was realized in the 0-stannyl ketyl-
promoted cyclopropane fragmentation-cyclization sequence shown in Scheme
3-9, where the C9-methyl endo:exo stereoselectivity was 57:1 in the 5-exo-trig
radical cyclization. Beckwith's chair-like transition state 246-247 explains the
endo-C9-methyl stereochemistry in 245, as shown in Scheme 3-10.16,17,36


HO HO H

0 TBTH, AIBN
PhH, reflux BU3nO

239 246

HO H HO H
H"Q CH3
TBTH ,.. "
Bu3SnO 3-Bu3Sn Bu3SnO

247 248

Scheme 3-10


In order to finally obtain a single triquinane diastereomer and simplify
characterization, PCC oxidation was performed to remove the C11 sp3
stereocenter of 245. The oxidation was complete in 1 hour, producing angular
triquinane diketone 249 in 78% yield, as shown in Scheme 3-11. In the 13C
NMR of 249, the C9-methyl was at 16.2 ppm and the C8 at 30.1 ppm. According
to Whitesell's studies,77 if the C9-methyl was endo, it should appear at about
15 ppm and the C8 at 30.1 ppm; if the C9-methyl was exo, it should be around
19 ppm and the C8 at about 34.5 ppm. The 13C NMR resonance for 249 was in
excellent agreement with that calculated for the endo-C9-methyl stereoisomer.
The endo stereochemistry of the C9-methyls in 245 and 249 was reconfirmed.










-.\-A'H PCC / -H
0 > CH2C 0 lH
78%
245 249

Scheme 3-11


This study examined the 0-stannyl ketyl-promoted cyclopropane
fragmentation-cyclization tandem sequence and a novel approach for angular
triquinane synthesis. Excellent stereoselectivity was accomplished. It is worth
noting the efficiency of this new method. The entire synthetic sequence is very
efficient, producing triquinane 245 in 5 steps in 46% overall yield from 173,
which can be prepared in 3 steps in 67% overall yield from 2-cyclohexen-l-one
178.
To synthesize precursor 238, which could lead to construction of a
model linear triquinane and another example of 0-stannyl ketyl-promoted
cyclopropane fragmentation-cyclization sequence, the approach shown in
Scheme 3-12 was planned.37


Br

0=0 CuBr2(1.4 eq)OO DBU
O O^ CHCI3, EtOAc MeCN
reflux, 46% 72%
250 251

S7 0 A/\VMgBr(l.3eq)_ 0
THF,-78C, 64% Y OH

252 238


Scheme 3-12







Starting material cis-1,5-dimethylbicyclo[3.3.0]octane-3,7-dione 250 was
prepared using Weiss condensation,78 as shown in Scheme 3-13. The 2:1
condensation of dimethyl 1,3-acetonedicarboxylate 253 and 2,3-butanedione
254 was carried out in an aqueous buffer solution of sodium bicarbonate (pH
8.3). Condensation product 255 gradually formed and separated from the
solution as white solid in 88% yield. The mechanism of this 2:1 condensation
has been discussed by Cook.79 Hydrolysis of 255 in a refluxing aqueous
mixture of HCI and HOAc yielded bicyclic dione 250 in 99% yield.

MeO2C CO2Me
MeO2C> O" nO CO2Me
M 20 OM NaHCO3 (aq.)HO OH
0:C + + 7 0 pH 8.3 HO
MeOC CO2Me 88% MeO2C CO2Me
253 254 253 255

HCI, HOAc, H20 0 0
reflux, 99%
250
Scheme 3-13


To prepare tricyclic dione 252, Gleiter's method was first used, as shown
in Scheme 3-12.80 Diketone 250 was monobrominated by adding 1.4
equivalent of CuBr2 to the refluxing reaction mixture. Copper(ll) bromide had to
be added very slowly in a very little amount each time, otherwise multiple-
bromination products would predominate. Monobromide 251 was produced in
46% yield. Because of the cup-like shape of molecule 250, bromide
approached primarily from the exo face, and so the bromide stereochemistry in
251 was exo. Treatment of 251 with 1.1 equivalent of DBU smoothly furnished







symmetrical tricyclic dione 252 in 72% yield.80 In this reaction, only the
deprotonation at one position could result in dehydrobromination, constructing
the fused cyclopropane unit in dione 252.
In order to improve the yield of 252, iodination of 250 was attempted.
Barluenga's methodology was used to prepare iodide 256, as shown in
Scheme 3-14.81 Iodide 256 was not characterized and purified. Crude iodide
256 was directly used to produce 252 in 51 % yield for these two steps. Thus,
the yield for 252 from 250 was increased from 33% (CuBr2 method) to 51%.


12(1.0 eq)
HgCI2 (0.5 eq) O4 I\
SO CH2CI2

250 256
00
DBU O
MeCN
51% for 2 steps
252

Scheme 3-14


12(1.1 eq)
0 0 Cu(OAc)2 (1.2 eq)
04 Oy HOAc, 600C *I O

250 256

DBU 0\
MeCN
25% for 2 steps
252

Scheme 3-15







Horiuchi's iodination methodology was also attempted, as shown in
Scheme 3-15.82 However, this iodination method was so messy that several
unknown side products also formed. Solvent acetic acid was difficult to remove.
The two-step yield from 250 to 252 was only 25%, much lower than that by

Barluenga's iodination method (Scheme 3-14).
The preparation of precursor 238 was straightforward from tricyclic
ketone 252, as shown in Scheme 3-12. Addition of 1.3 equivalent of 3-
butenylmagnesium bromide to 252 at -78C afforded 238 in 64% yield.

Because of its cup-like molecule shape, the incoming Grignard reagent could
approach 252's carbonyls only from the exo face. This exo:endo face selectivity
was >100:1 by GC. This stereoselective addition of the Grignard reagent to the
most accessible exo face was important for later elaboration to the cis,anti,cis-
configuration of the model linear triquinane skeleton. Due to the C2 symmetry of

252, same addition product was obtained no matter which carbonyl group

reacted.
0-stannyl ketyl-promoted cyclopropane fragmentation-cyclization tandem
sequence using precursor 238 was examined, as shown in Scheme 3-16.37
Refluxing 238 in benzene at a concentration of 0.25 M overnight, with 3
equivalents of TBTH and 1 equivalent of AIBN, gave linear triquinane 259 in
83% yield. The exo stereochemistry of the olefin tether in 238 secured the
requisite cis,anti, cis-configuration in 259, which occurs in all natural linear
triquinane compounds. The newly formed C9-methyl (13.7 ppm in 13C NMR)
was established as endo for the major product, by comparison with 13C NMR
studies of closely related fused-cyclopentanes.77 If the C9-methyl was endo, its
resonance should be around 15 ppm. If it was exo, its resonance should be at
about 20 ppm.77 This C9-methyl endo:exo stereoselectivity in the 5-exo-trig
radical cyclization was 4:1 by GC. This endo-C9-methyl stereoselectivity can be







explained using Beckwith's chair-like transition state 257-258, as shown in
Scheme 3-16.16,17,37



O0 TBTH, AIBN OH
Bu3SnO
OH PhH, reflux 3 "
83%
238 257
H
.,,H 0 9 8
Bu3SnO 10/


258 259

Scheme 3-16


In conclusion, it is demonstrated that the 0-stannyl ketyl-promoted
cyclopropane fragmentation-cyclization tandem sequences work very well.
These sequences are highly stereoselective and the stereochemistry of their
products can be predicted with accuracy. The yields of these sequences are
excellent, considering the complexity of their products. Through these two
examples, a novel and efficient synthetic approach toward angular and linear
triquinane compounds is demonstrated. The work in this chapter marked the
first real synthetic application of the 0-stannyl ketyl-promoted cyclopropane
fragmentations and enhances our understanding and knowledge of 0-stannyl
ketyl radicals.













CHAPTER 4
OTHER INVESTIGATIONS OF THE 0-STANNYL KETYL-PROMOTED
CYCLOPROPANE FRAGMENTATIONS


0-stannyl ketyl-promoted cyclopropane fragmentations were studied
using a variety of substrates in previous chapters. In all the cases, after
fragmentations, the radical centers were reduced by hydrogen abstraction from
TBTH, and the tin(IV) enolates were hydrolyzed, though these radicals and
enolates were synthetically useful. This chapter reports our preliminary results
of application of the post-fragmentation tin(IV) enolates and trapping the post-
fragmentation radicals with allyltributyltin.


Application of the Post-Fragmentation Tin(IV) Enolates


Tin(IV) enolates are useful intermediates and have been applied to many
synthetic transformations.6g,83 Recently Enholm demonstrated that tin(IV)
enolates can be smoothly generated by the reaction of TBTH and a,3-

unsaturated ketones,34 as illustrated in Scheme 1-23. These tin(IV) enolates
function very well in aldol and alkylation reactions.
It has been well known since early 1970s that 0-stannyl ketyl-promoted
cyclopropane fragmentations readily generate tin(IV) enolates 133,25-27 as
shown in Scheme 4-1. However, prior to the work described in this chapter, no
synthetic exploration of this post-cyclopropane-fragmentation tin(IV) enolates
had been reported. We envisioned that these tin(IV) enolates could be








synthetically useful by reacting with an electrophile, such as an aldehyde,
ketone or alkyl halide, forming a new carbon-carbon bond.


0



130


OSnBu3 OSnBu3
TBTH R
AIBN


131


132


TBTH
- Bu3Sn.


OSnBu3

R13

133 H


0

R

0E H


Scheme 4-1


To examine synthetic application of these tin(IV) enolates, an aldol
reaction was performed using cyclopropyl ketone 137. The cyclopropane
fragmentation finished in 2 hours, monitored by TLC. At room temperature,
benzaldehyde 262 was added to tin(IV) enolate 261 and the reaction mixture


0 OSnBu3
.^f^^ TBTH E
AIBN PhCHO (262)
MO 4 PhH, 800C MO Et 97%
MeO137 2hrs Me 261


0 OH



MeO Et K M
263E (4.4:1)


263T


Scheme 4-2







was stirred overnight, giving 263E/263T in 97% yield as a mixture of erythro
and threo diastereomers (4.4:1 by proton NMR integration), as shown in
Scheme 4-2. The stereochemical assignment (erythro or threo) was made by
1 H NMR, using the well-accepted Jthreo > Jerythro relationship.84 For the

major product, the coupling constant between the carbinol proton and the
methine proton was 4.5Hz; for the minor product, the coupling constant was
6.9Hz. Thus, the major product was assigned as erythro (263E). This
assignment was confirmed by 13C NMR spectra. According to Heathcock's
studies,85 the carbinol resonance of erythro P-hydroxycarbonyl compounds
should be at 71.6-78.1 ppm and that of threo isomer should be higher at 74.0-
82.5 ppm. The carbinol of the major product appeared at 73.8 ppm, while the
carbinol of the minor product was at 75.6 ppm. The erythro assignment for the
major product was thus confirmed. This is the first known 0-stannyl ketyl-
promoted cyclopropane fragmentation-aldol reaction.
A similar aldol reaction of tin(IV) enolate 261 and cyclohexanecarbox-
aldehyde 264 gave 265 in 92% yield, as shown in Scheme 4-3. A single
diastereomer was isolated in excellent selectivity (>46:1 by GC).


0 OSnBu3
TBTH N
SAIBN
MeO PhH ,800C MeO Et
137 2hrs 261
/ \ 0 OH
(264) H
H I N.
92% Et (>46:1)
MeO
265


Scheme 4-3







Alkylation reactions were also performed using tin(IV) enolate 261, as
shown in Scheme 4-4. When the cyclopropane fragmentation finished in 2
hours, 5 equivalents of HMPA were added at room temperature to increase the
nucleophilicity of the enolate.34c,d Alkyl halide was next added and the mixture
was refluxed overnight, giving alkylation product 267 (86%) and 268 (95%) in
excellent yields. These are the first 0-stannyl ketyl-promoted cyclopropane
fragmentation-alkylation reactions.


0 OSnBu3
SLTBTH .-
I AIBN
MeO PhH, 800C MeO Et
137 2hrs 261
0

1) HMPA (5 eq.) R
2) RX, reflux Et
MeO Et
266

RX alkylation product isolated yield

V Br 267 86%

V VVV 268 95%

Scheme 4-4


In a summary, tin(IV) enolates generated in the reactions of cyclopropyl
ketones and TBTH are synthetically useful and work well in aldol and alkylation
reactions. This exploration adds new depth to the 0-stannyl ketyl-promoted
cyclopropane fragmentations.







Cvclopropane Fragmentation-Allylation by Allyltributyltin


Chapter 1 has introduced Keck's allylation reactions (Schemes 1-8 and
1-9).14 Historically, this allylation method dates back to 1973 when Migita and
Pereyre first reported the free radical chain reaction of allylstannanes and
organic halides.86 In these reactions, a free radical was trapped by an allyl
group, and a new carbon-carbon bond formed between the radical site and the
allyl unit, as shown in Scheme 1-8. The first systematic investigation of this
reaction was published in 1975.87 In 1982, Keck demonstrated that this
allylation reaction worked well in complicated substrates, tolerating the
presence of acetals, ketals, ethers, epoxides, lactones, free hydroxyl groups,
esters and sulfonate esters.14a Besides organic halides, Keck realized the
allylation reactions of thioethers, thiocarbonyl esters and selenides. Keck found
methallyltributyltin also suitable for this type of reaction.1 4b



SO ysOBn Bu0S O OBn
0 BuS ~ -- I(eq. 17)
PhO O '. 80-93% :,.,0
269 270
Br..

): US ___ ) (eq. 18)
0J AIBN, PhH, reflux (eq18)
271 C02Me 90% 272 C02Me
Scheme 4-5


Since then, this allylation method has steadily found further
investigations and synthetic applications.88 For example, Keck applied it to the







synthesis of pseudemonic acid C, as shown in eq. 17 in Scheme 4-5.88e
Hanessian utilized this allylation method to prepare 6-a-allyl penicillanates
272, as shown in eq. 18.88f
In 1985 Moriya applied allyltributyltin to radical cyclizations.89 A typical
free radical cyclization uses TBTH. The last step of this cyclization is reductive
hydrogen abstraction by cyclized carbon-centered radical from TBTH. When
allyltributyltin is used for cyclization, the hydrogen abstraction step is modified to
a new carbon-carbon bond formation, without sacrificing the free radical chain
process, as shown in Scheme 4-6. The chain process is maintained by
regenerating tributyltin radical through an SH2' reaction between cyclized
radical 275 and allyltributyltin. Overall, an alkene-tethered ring 276 is
produced in this reaction.



YBu3Sn v
CJ AIBN, PhH, reflux
49%
273 274



C3 ~- Bu3Sn.
275 276

Scheme 4-6


A similar cyclization was examined by Curran, as shown in Scheme 4-
7.90 Curran used acylsilane as a radical acceptor. After the 6-exo cyclization,
radical 279 rearranged to 280 which finally reacted with allyltributyltin to
produce 281 in 60% yield.








SiPh2Me SiPh2Me SiPh2Me
0 BU3Sn 0__0
AIBN, PhH, reflux
60%
277 278 279

0% e BU3Sn/'/ .OSiPh2Me
__^ SiPh2Me Bu3Sn /
a- BU3Sn. -
280 281
Scheme 4-7


An interesting application of allyltributyltin is Mizuno's double vicinal
carbon-carbon bond-forming reaction on electron-deficient alkenes by
allyltributyltin and alkyl iodide, as shown in Scheme 4-8.91 The mixture of
dicyano alkene 282, allyltributyltin 29 and iodomethane 283 in 1:2:5 ratio was
refluxed in benzene. The reaction was complete in 6 hours, affording 284 as
the sole product in 85% yield. The allyl unit from allyltributyltin was
regioselectively introduced to the a-carbon of dicyanoethene 282, and the
methyl group from iodomethane 283 to the P-carbon. This three-component
coupling reaction inserted two different carbon-functional groups across a
double bond in one step.

Ph Bu3Sn I-CH3 AIBN Ph H3

NC CN PhH, reflux N CT
282 29 283 85% C N 284


Scheme 4-8







In order to expand the application scope of 0-stannyl ketyl-promoted
cyclopropane fragmentations, allyltributyltin chemistry was combined with our
cyclopropane fragmentation studies. The allyltributyltin-induced cyclopropane
fragmentation was unknown prior to the work described in this chapter. This
fragmentation-allylation reaction is illustrated in Scheme 4-9. The primary
process is AIBN-initiated formation of tributyltin radical 5 from allyltributyltin 29.
Radical 5 adds to the carbonyl of cyclopropyl ketone 130, giving 0-stannyl ketyl
species 131. The cyclopropane fragments to afford radical 132. This
intermediate attacks allyltributyltin 29 to acquire its allyl unit through an SH2'

substitution and regenerate tributyltin radical 5 to continue the chain reaction.
Fragmentation-allylation product 285 is thus produced.



OSnBu3 Bu3Sn AigN 0

R "0 29 eSnBu3 130V
5
285

u OSnBu3

R -0 131
OSnBOu
Bu3Sn R :_" 00101
29 132

Scheme 4-9


To examine this fragmentation-allylation reaction, ketones 137 and 171
were refluxed with allyltributyltin and AIBN in benzene. The desired
fragmentation-allylation products 286 (50%) and 287 (94%) were isolated, as







shown in Scheme 4-10. These are the first allyltributyltin-induced cyclopropane
fragmentation-allylation reactions.

0 0
op, Bu3Sn /
Ne J AIBN, PhH, reflux NI
MeO 50% MeO
137 286
CO2Et
O~u3Sn
C02Et // A H (
94% BU3Snn H
AIBN, PhH, reflux
94% BUHSnO H H
171 H H 203
C ,C02Et
BuaSn"V H a, C

-Bu3Sn. H 7 O l'

Ha 287

Scheme 4-10


The stereochemistry of 287 was assigned on the basis of the structure
of 204L (Figure 2-8) and was confirmed by NOE (nuclear Overhauser effect)
difference NMR spectrum.92 Positive NOE difference was observed for the b-
protons at C2 and C4 methylenes when the allylic methylene (Ca) protons were
irradiated. Excellent stereoselectivity in the allyl abstraction from allyltributyltin
was achieved for radical intermediate 203. This stereoselectivity could be
rationalized with the steric difference between the L face and the R face of 203
for approaching allyltributyltin molecule.





77

In a summary, the 0-stannyl ketyl-promoted cyclopropane fragmentation-

allylation works well using allyltributyltin. This reaction forms a new carbon-

carbon bond by introducing an allyl unit.

The preliminary study described in this chapter exhibits the duality of the
free radical and tin(IV) enolate species generated in the 0-stannyl ketyl-

promoted cyclopropane fragmentations. Obviously, further synthetic efforts to

capitalize on both species will definitely lead to exciting developments in this

area.













CHAPTER 5
SUMMARY


The studies described in this dissertation are an attempt to expand the
realm of free radical chemistry. The mild reaction conditions and the ability to
control the reactivity, stereoselectivity and regioselectivity in these reactions
have made free radical methodologies valuable and indispensable in organic
synthesis. Much current free radical chemistry has been dominated by halogen
and group abstractions as the source of organic radicals. The halogen or group
functionality is usually lost in these classical free radical reactions. The reaction
of TBTH and carbonyls provides a unique 0-stannyl ketyl radical, which
behaves like a pseudo-protected az-oxygen-functionalized radical. The original

oxygen functionality is well preserved in its reactions, leading to alcohols or
ketones. It makes 0-stannyl ketyl radical especially attractive and provides
advantages over classical free radicals. However, the 0-stannyl ketyl chemistry
is not well-understood yet, and its synthetic applications are still limited. The

goal of this dissertation is to enhance our understanding of this ketyl species by
studying the cyclopropane fragmentations and their synthetic applications.

Chapter 2 examined the 0-stannyl ketyl-promoted cyclopropane
fragmentations using a variety of cyclopropyl ketone precursors. The
fragmentations were governed by both stereoelectronic effects and relative
stability of the fragmentation radical products. The significance of radical-
stability effects depended on the substitution pattern of the cyclopropane. These








studies enabled us to design synthetic methodologies to utilize the special
merits of cyclopropane fragmentations.
Chapter 3 demonstrated our 0-stannyl ketyl-promoted cyclopropane
fragmentation-cyclization tandem sequence. This was the first synthetic

application of 0-stannyl ketyl-promoted cyclopropane fragmentations.
Triquinane terpenes had been among the most interesting and challenging
natural products for synthetic chemists for over two decades. Their unique
cis,trans,cis angularly- or linearly-fused tricyclopentanoid skeletons had served
as a testing vehicle for a wide variety of synthetic methodologies. The
cyclopropane fragmentation-cyclization sequence was examined in the
synthesis of a model angular triquinane and a model linear triquinane. The
synthesis was successful and efficient. Very good regioselectivity and
stereoselectivity were accomplished in both tandem sequences. This study
demonstrated a novel synthetic route to triquinane compounds.
Chapter 4 reported preliminary results of two new investigations. The
tin(IV) enolate formed in the cyclopropane fragmentations was examined. Its
aldol and alkylation reactions were accomplished in excellent yield. The
reaction of allyltributyltin with cyclopropyl ketones was performed. The 0-

stannyl ketyl-promoted cyclopropane fragmentation-allylation was successful.
These preliminary results added new depth to 0-stannyl ketyl chemistry and the
cyclopropane fragmentation methodologies.

Collectively, these studies have extended the understanding and
applications of 0-stannyl ketyl chemistry. This work has established the use of
0-stannyl ketyl-promoted cyclopropane fragmentations in organic synthesis.













CHAPTER 6
EXPERIMENTAL


General Methods


Infrared spectra were recorded on a Perkin-Elmer 1600 FT-IR
spectrometer and are reported in wave numbers (cm-1). 1H NMR spectra were
recorded on a Varian Gemini-300 (300 MHz) or a General Electric QE-300 (300
MHz) spectrometer. 13C NMR spectra were recorded at 75 MHz on the above-
mentioned spectrometers. Chemical shifts are reported in ppm down field
relative to tetramethylsilane as an internal standard in CDCI3. Elemental

analysis was performed by the Atlantic Microlab Inc., Norcross, Georgia or by
the Elemental Analysis Service at the Department of Chemistry, University of
Florida, Gainesville, Florida. The high resolution mass spectroscopy (HRMS)
was performed by the Mass Spectroscopy Service at the Department of
Chemistry, University of Florida, Gainesville, Florida.
All reactions were run under inert atmosphere of argon using oven dried

apparatus. All yields reported refer to isolated material judged to be
homogeneous by thin layer chromatography (TLC) and NMR spectroscopy.

Solvents were dried according to established procedures by distillation under
inert atmosphere from appropriate drying agents.
Analytical TLC was performed with Aldrich Z12272-6 precoated silica gel
plates (0.25 mm) using 254 nm UV light, p-anisaldehyde in ethanol with acetic
acid or phosphomolybdic acid in ethanol as indicator. Column chromatography







was performed using Merck silica gel 60 (230-400 mesh) by standard flash
chromatographic techniques. GC experiments were performed on a Varian
3500 capillary gas chromatograph using a J & W fused silica capillary column
(DB5-30W; film thickness 0.25 p.).


Experimental Procedures and Results


1-Dodecen-3-ol (141). Decyl aldehyde (5.00 g, 32.1 mmol) was dissolved in
THF (50 mL). This solution was chilled to -78C. Vinylmagnesium bromide (1.0
M in THF, 65.0 mL, 65.0 mmol) was added to the solution dropwise through a
syringe. The reaction was complete in 1 hour and quenched by ice chips and
NH4CI (aq.). The mixture was extracted with ether. The ether phase was dried,
rotovaped and subjected to flash column chromatography to give 141 (6.13 g,
100%) as a clear oil. Rf (1:4 ether/hexane) 0.31. 1H NMR 8 5.86 (m, 1H), 5.20
(d, J=1 7 Hz, 1 H), 5.08 (d, J=1 1 Hz, 1 H), 4.08 (m, 1 H), 2.00 (s, 1 H), 1.52-1.50 (m,
2H), 1.27 (m, 10H), 0.90-0.83 (m, 7H); 13C NMR 5 141.4, 114.3, 73.2, 37.0,
31.9, 29.5 (3C), 29.3, 25.3, 22.6, 14.0. Anal. Calcd for C12H240: C, 78.18; H,
13.13. Found: C, 78.38; H, 13.16.
1.6E-Dodecadien-3-ol (142). Trans-4-Decenal (1000 mg, 6.49 mmol) was
dissolved in THF (13 mL). This solution was chilled to -78C. Vinylmagnesium
bromide (1.0 M in THF, 13.0 mL, 13.0 mmol) was added to the solution
dropwise with a syringe. The reaction was complete in 1 hour and quenched by
ice chips and NH4CI (aq.). The mixture was extracted with ether. The ether
phase was dried, rotovaped and chromatographed to afford 142 (1194 mg,
100%) as a clear oil. Rf (1:4 ether/hexane) 0.37. 1H NMR 8 5.86 (m, 1H), 5.43
(m, 2H), 5.22 (d, J=17 Hz, 1H), 5.10 (d, J=10 Hz, 1H), 4.11 (m, 1H), 2.11-2.05
(m, 2H), 1.97 (m, 2H), 1.86 (d, J=4.5 Hz, 1H), 1.58 (m, 2H), 1.39-1.28 (m, 6H),








0.88 (t, J=7 Hz, 3H); 13C NMR 8 141.1, 131.2, 129.3, 114.5, 72.6, 36.7, 32.5,
31.3, 29.2, 28.5, 22.5, 14.0. Anal. Calcd for C12H220: C, 79.06; H, 12.16.
Found: C, 79.11;H, 12.18.
Preparation of 1-Dodecen-3-one (143) bv Swern oxidation.48 Oxalyl chloride
and DMSO were freshly distilled. Oxalyl chloride (2.09 mL, 23.9 mmol) was
dissolved in CH2CI2 (24 mL) in a 3-necked flask and chilled to -60C. Through
an additional funnel, a solution of DMSO (3.70 mL, 52.2 mmol) in CH2CI2 (14
mL) was carefully dripped to the flask to maintain the inside temperature at
-60C. The reaction mixture was then stirred for 15 minutes. A solution of allyl
alcohol 141 (2000 mg, 10.9 mmol) in CH2CI2 (11 mL) was dropwise added to
the flask through the additional funnel to maintain the inside temperature
constantly at -60C. The reaction mixture was stirred for 30 minutes.
Triethylamine (7.6 mL, 54.3 mmol) was added to the flask. After 5 minutes, the
chilling bath was removed to allow the reaction mixture to warm up gradually.
Water was added to quench to reaction. The mixture was extracted multiply with
CH2CI2. The organic phase was washed with water, dried and rotovaped. The
residue was subjected to flash column chromatography to yield 143 (1030 mg,
52%) as a clear oil. Rf (1:3 ether/hexane) 0.56. 1H NMR 8 6.36 (m, 1 H), 6.21 (d,

J=18 Hz, 1H), 5.80 (d, J=11 Hz, 1H), 2.58 (t, J=7.5 Hz, 2H), 1.62 (m, 2H), 1.27
(m, 12H), 0.88 (t, J=6 Hz, 3H); 13C NMR 8 200.9, 136.5, 127.6, 39.6, 31.8, 29.3
(2C), 29.2 (2C), 23.9, 22.6, 14.0. HRMS for C12H220 M+H, calcd: 183.1749.

Found: 183.1743.
Preparation of 1-Dodecen-3-one (143) by Tsuii's allyl methyl carbonate
method.49 A mixture of allylic alcohol 141 (1000 mg, 5.42 mmol), allyl methyl
carbonate (1234 pL, 10.88 mmol), catalyst RuH2(PPh3)4 (62 mg, 0.054 mmol)
and toluene (26 mL) was refluxed for 12 hours. Toluene was then rotovaped







away. The dark residue was chromatographed to afford 143 (833 mg, 83%) as
a clear oil. Rf (1:3 ether/hexane) 0.56.
Preparation of 1.6E-Dodecadien-3-one (144) by Swern oxidation.48 Oxalyl
chloride (2.11 mL, 24.2 mmol) was dissolved in CH2CI2 (24 mL) in a 3-necked
flask and chilled to -60C. A solution of DMSO (3.74 mL, 52.8 mmol) in CH2CI2
(14 mL) was carefully dripped to the flask through an additional funnel, to
maintain the inside temperature at -60C. The reaction mixture was then stirred
for 15 minutes. A solution of allyl alcohol 142 (2000 mg, 11.0 mmol) in CH2CI2
(11 mL) was dropwise added to the flask through the additional funnel to
maintain the inside temperature constant. The reaction mixture was stirred for
30 minutes. Triethylamine (7.7 mL, 55.0 mmol) was added to the flask. After 5
minutes, the chilling bath was removed to allow the reaction mixture to warm up
gradually. Water was added to quench to reaction. The mixture was extracted
multiply with CH2CI2. The organic phase was washed with water, dried and
rotovaped. The residue was chromatographed to give 144 (1037 mg, 52%) as
a clear oil. Rf (1:3 ether/hexane) 0.47. 1H NMR 8 6.36 (m, 1 H), 6.21 (d, J=17 Hz,
1H), 5.82 (d, J=10 Hz, 1H), 5.43 (m, 2H), 2.65 (t, J=7 Hz, 2H), 2.31 (m, 2H), 1.96
(m, 2H), 1.33-1.27 (m, 6H), 0.88 (t, J=6 Hz, 3H); 13C NMR 8 200.2, 136.5, 131.6,
128.2, 127.8, 39.5, 32.4, 31.3, 29.1, 26.9, 22.5, 14.0. HRMS for C12H200,
calcd: 180.1514. Found: 180.1513. Anal. Calcd for C12H200: C, 79.94; H,
11.18. Found: C, 79.70; H, 11.22.
Preparation of 1.6E-Dodecadien-3-one (144) by Tsuji's allyl methyl carbonate
method.49 A mixture of allylic alcohol 142 (1000 mg, 5.49 mmol), allyl methyl
carbonate (1247 IL, 10.98 mmol), catalyst RuH2(PPh3)4 (63 mg, 0.055 mmol)
and toluene (28 mL) was refluxed for 12 hours. The mixture was rotovaped to
remove toluene. The dark residue was chromatographed to afford 144 (683
mg, 69%) as a clear oil. Rf (1:3 ether/hexane) 0.47.







Preparation of 1-cyclopropyldecan-l-one (135) by Scheme 2-2. NaH (60%, 57
mg, 1.43 mmol) was placed in a Schlenk flask, washed with n-pentane (x3) and
pumped. Trimethyloxosulfonium iodide (315 mg, 1.43 mmol) was added. DMSO
(2 mL) was dripped to the stirred solid mixture through a syringe. After hydrogen
evolution, a milky solution turned clear and was stirred for 15 minutes. Ketone
143 (200 mg, 1.10 mmol) in 1 mL DMSO was added. The mixture was stirred
for 12 hours and quenched with water. The mixture was extracted with ether.
The ether layer was dried, rotovaped, and chromatographed to give 135 (39
mg, 18%) as an oil. Rf (1:3 ether/hexane) 0.70. 1H NMR 8 2.48 (t, J=7 Hz, 2H),
1.87 (m, 1H), 1.55 (m, 2H), 1.21 (m, 12H), 0.94 (m, 2H), 0.82-0.77 (m, 5H); 13C
NMR 8 211.1,43.4, 31.8, 29.4 (2C), 29.2 (2C), 24.0, 22.6, 20.2,14.0, 10.4 (2C).
HRMS for C 3H240, calcd: 196.1827. Found: 196.1894.
Preparation of 1-cyclopropyl-4E-decen-1-one (136) by Scheme 2-2. NaH
(60%, 130 mg, 3.25 mmol) was placed in a Schlenk flask, washed with n-
pentane (x3) and pumped. Trimethyloxosulfonium iodide (715 mg, 3.25 mmol)
was added. DMSO (11 mL) was dripped to the stirred solid mixture through a
syringe. After hydrogen evolution, a milky solution turned clear and was stirred
for 15 minutes. Ketone 144 (450 mg, 2.50 mmol) in 1 mL DMSO was added.
The mixture was stirred for 12 hours and quenched with water. The mixture was
extracted with ether. The ether layer was dried, rotovaped and subjected to
column chromatography to give 136 (115 mg, 24%) as a clear oil. Rf (1:3
ether/hexane) 0.71. 1H NMR 5 5.38 (m, 2H), 2.57 (t, J=7 Hz, 2H), 2.25 (q, J=7
Hz, 2H), 1.95-1.85 (m, 3H), 1.34-1.24 (m, 6H), 0.97 (m, 2H), 0.87-0.79 (m, 5H);
13C NMR 5 210.3, 131.4, 128.3, 43.2, 32.4, 31.2, 29.1, 26.9, 22.4, 20.2, 13.9,

10.4 (2C). HRMS for C13H220 M+H, calcd: 195.1749. Found: 195.1764.
1-Cvclopropvldecan-1-ol (145). Magnesium turning (185 mg, 7.69 mmol) was
finely ground in a dry mortar and placed in a 3-necked flask equipped with a







condenser, an additional funnel and a stirring bar. A bit of iodine crystal was
added to the turning. Cyclopropyl bromide (308 l.L, 3.85 mmol) was dissolved
in 4 mL THF and added into the additional funnel. About one third of the
solution was dripped to the stirred turning. When the reaction started releasing
heat and bubbles, the remaining cyclopropyl bromide solution was added
dropwise. The mixture was heated in 65C oil bath for 20 minutes. At room
temperature, aldehyde 139 (200 mg, 1.28 mmol) was added. The mixture was
stirred for 1 hour and quenched with NH4CI (aq.). The mixture was extracted
with ether. The ether layer was dried, rotovaped and chromatographed to yield
145 (193 mg, 76%) as an oil. Rf (1:1 ether/hexane) 0.59. 1H NMR 8 2.78 (m,
1 H), 1.93 (s, 1 H), 1.51 (m, 2H), 1.41-1.20 (m, 15H), 0.81 (t, J=7 Hz, 3H), 0.42 (m,
2H), 0.16 (m, 2H); 13C NMR 8 76.7, 37.2, 31.8, 29.7, 29.5 (2C), 29.2, 25.7, 22.6,
17.8, 14.0, 2.6, 2.3. HRMS for C13H260, calcd: 198.1984. Found: 198.1880.
1-Cyclopropyl-4E-decen-1-ol (146). Magnesium turning (187 mg, 7.79 mmol)
was finely ground in a dry mortar and placed in a 3-necked flask equipped with
a condenser, an additional funnel and a stirring bar. A bit of iodine crystal was
added to the turning. Cyclopropyl bromide (312 pL, 3.90 mmol) was dissolved
in 4 mL THF and added into the additional funnel. About one third of the
solution was dripped to the stirred turning. When the reaction started releasing
heat and bubbles, the remaining cyclopropyl bromide solution was added
dropwise. The mixture was heated in 65C oil bath for 20 minutes. At room
temperature, aldehyde 140 (200 mg, 1.30 mmol) was added. The mixture was
stirred for 1 hour and quenched with NH4CI (aq.). The mixture was extracted
with ether. The ether layer was dried, rotovaped and chromatographed to afford
146 (178 mg, 70%) as an oil. Rf (1:1 ether/hexane) 0.58. 1H NMR 8 5.36 (m,

2H), 2.81 (m, 1H), 2.07 (m, 2H), 1.91 (m, 3H), 1.60 (m, 2H), 1.22 (m, 6H), 0.82
(m, 4H), 0.43 (m, 2H), 0.18 (m, 2H); 13C NMR 8 130.8, 129.7, 76.2, 37.0, 32.5,







31.3, 29.2, 28.8, 22.4, 17.8, 14.0, 2.6, 2.4. HRMS for C13H240, calcd:

196.1827. Found: 196.1819.
Preparation of 1-cyclopropyldecan-l-one (135) by Scheme 2-4. Alcohol 136
(274 mg, 1.38 mmol) was dissolved in CH2CI2 (3 mL). To this solution was

added finely ground mixture of PCC (598 mg, 2.77 mmol) and silica gel (600
mg). The oxidation was complete in 4 hours and diluted with a large amount of
ether. The ether solution was forced through a celite bed and the bed was
rinsed with ether. The ether solution was rotovaped and chromatographed to
yield 135 (224 mg, 83%) as an oil. Rf (1:3 ether/hexane) 0.70.
Preparation of 1-cyclopropyl-4E-decen-1-one (136) bv Scheme 2-4. Alcohol
146 (150 mg, 0.765 mmol) was dissolved in CH2CI2 (1.5 mL). To this solution
was added finely ground mixture of PCC (330 mg, 1.53 mmol) and silica gel
(330 mg). The oxidation was complete in 4 hours and diluted with a large
amount of ether. The ether solution was forced through a celite bed and the bed
was rinsed with ether. The ether solution was rotovaped and chromatographed
to give 136 (116 mg, 78%) as an oil. Rf (1:3 ether/hexane) 0.71.
Phenvyl(trans-2-phenylcyclopropyvl)methanone (138). NaH (60%, 231 mg, 5.77
mmol) was placed in a 3-necked flask, washed with n-pentane (x3) and fully
pumped. Trimethyloxosulfonium iodide (1270 mg, 5.77 mmol) was added.
DMSO (10 mL) was dripped to the solid mixture through an additional funnel.
After hydrogen evolution, a milky solution turned clear and was stirred for 15
minutes. Trans-chalcone 147 (1000 mg, 4.81 mmol) was added. The mixture
was stirred for 20 hours and quenched with water. The mixture was extracted
with ether. The ether layer was dried, rotovaped, and chromatographed to give
138 (1080 mg, 100%) as a white solid. Rf (1:3 ether/hexane) 0.48. 1H NMR 5
8.01-7.98 (m, 2H), 7.59-7.56 (m, 1H), 7.49-7.43 (m, 2H), 7.35-7.29 (m, 2H), 7.25-
7.22 (m, 1H), 7.21-7.17 (m, 2H), 2.91 (m, 1H), 2.70 (m, 1H), 1.93 (m, 1H), 1.56







(m, 1H); 13C NMR 8 198.5, 140.5, 137.8, 132.9, 128.5 (4C), 128.1 (2C), 126.6
(2C), 126.2, 30.0, 29.3, 19.2. HRMS for C16H140, calcd: 222.1045. Found:
222.1056.
Tridecan-4-one (148L. A mixture of cyclopropyl ketone 135 (200 mg, 1.02
mmol), TBTH (549 IL, 2.04 mmol) and AIBN (84 mg, 0.51 mmol) in benzene (3
mL) was degassed by argon stream for 15 minutes. The mixture was refluxed at
80C for 18 hours. A DBU workup procedure was used to remove excess TBTH
and other tin byproducts.34d,93 The reaction mixture was diluted with ether.
Following addition of DBU (335 pL, 2.24 mmol) and 2-3 drops of water, an
ethereal solution of iodine was added dropwise until the iodine orange color
persisted. Rapid suction filtration through silica gel bed was performed. The
silica gel bed was rinsed with ether, and the solution was concentrated and
subjected to flash column chromatography to afford 148 (162 mg, 80%) as an
oil. Rf (1:3 ether/hexane) 0.47. 1H NMR 2.35 (m, 4H), 1.62-1.53 (m, 4H), 1.40-
1.23 (m, 12H), 0.92-0.85 (m, 6H), identical to that published in Sadtler NMR
Spectra (#23462);94 13c NMR 8 211.6, 44.7, 42.8, 31.9, 29.4 (2C), 29.3 (2C),
23.9, 22.7, 17.3, 14.1, 13.8, identical to that published in Sadtler 13C NMR
Spectra (#5994).95 HRMS for C1 3H260, calcd: 198.1984. Found: 198.1987.
7E-Tridecen-4-one (149). A mixture of cyclopropyl ketone 136 (100 mg, 0.515
mmol), TBTH (277 gL, 1.03 mmol) and AIBN (42 mg, 0.258 mmol) in benzene (2
mL) was degassed by argon stream for 15 minutes. The mixture was refluxed at
80C for 18 hours. The reaction mixture was rotovaped and subjected to flash
column chromatography to give 149 (81 mg, 80%) as an oil. Rf (1:3
ether/hexane) 0.63. 1H NMR 8 5.33 (m, 2H), 2.40-2.28 (m, 4H), 2.24-2.15 (m,
2H), 1.88 (m, 2H), 1.52 (m, 2H), 1.28-1.20 (m, 6H), 0.86-0.78 (m, 6H); 13C NMR
8 210.8, 131.5, 128.3, 44.8, 42.6, 32.4, 31.3, 29.1, 26.8, 22.5, 17.2, 14.0, 13.7.
HRMS for C13H240, calcd: 196.1827. Found: 196.1808.







1-(4-Methoxyphenyl)-1l-butanone (150). A mixture of cyclopropyl ketone 137
(200 mg, 1.14 mmol), TBTH (458 gL, 1.70 mmol) and AIBN (56 mg, 0.341 mmol)
in benzene (2.5 mL) was degassed by argon stream for 15 minutes. The mixture
was refluxed at 80C for 2 hours. The reaction mixture was rotovaped and
chromatographed to afford 150 (186 mg, 92%) as a solid. Rf (1:1 ether/hexane)
0.71. 1 H NMR 5 7.85 (d, J=9 Hz, 2H), 6.83 (d, J=9 Hz, 2H), 3.76 (s, 3H), 2.80 (t,
J=7 Hz, 2H), 1.66 (m, 2H), 0.91 (t, J=7 Hz, 3H); 13C NMR 8 198.7, 163.1, 130.0
(3C), 113.4 (2C), 55.2, 39.9, 17.8, 13.7. HRMS for C11 Hi1402, calcd: 178.0994.
Found: 178.0993.
1.4-Diphenylbutan-l-one (151). A mixture of compound 138 (200 mg, 0.901
mmol), TBTH (727 IL, 2.70 mmol) and AIBN (148 mg, 0.901 mmol) in benzene
(4.5 mL) was degassed by argon stream for 15 minutes. The mixture was
refluxed at 80C for 5 hours. Quenched with ethanol, the reaction mixture was
rotovaped and chromatographed to afford 151 (173 mg, 86%) as a clear liquid
which slowly solidified. Rf (1:3 ether/hexane) 0.42. 1H NMR 5 7.90-7.87 (m, 2H),
7.52-7.46 (m, 1H), 7.41-7.36 (m, 2H), 7.29-7.23 (m, 2H), 7.19-7.14 (m, 3H), 2.92
(t, J=7 Hz, 2H), 2.69 (t, J=7 Hz, 2H), 2.05 (m, 2H); 13C NMR 8 199.8, 141.5,
136.9, 132.7, 128.4 (2C), 128.3 (2C), 128.2 (2C), 127.8 (2C), 125.8, 37.5, 35.0,
25.5. HRMS for C16H160, calcd: 224.1201. Found: 224.1225.
3-Methoxycarbonyl-2-cyclohexen-1-one(159).52 This synthetic work was
identical to that described by Lange and Otulakowski.52 A 3-necked flask
equipped with an additional funnel, a condenser and a thermometer was used.
Cyclohexanecarboxylic acid 156 (25.0 g, 195 mmol) was placed in the flask.
Freshly distilled thionyl chloride (17.4 mL, 238 mmol) was dropwise added
through the additional funnel in 30 minutes. This mixture was refluxed for 2
hours. Red phosphorus (310 mg, 10.0 mmol) was added with stirring. The
temperature was increased to 90C and bromine (12.3 mL, 238 mmol) was







dropwise added in 1.5 hour as the temperature was maintained below 105C.
The mixture was heated at 100C for an additional hour and then chilled to 5C.
Anhydrous methanol (40 mL, 989 mmol) was dropwise added. The mixture was
refluxed for 15 minutes, cooled, and poured into ice-cold water. The mixture
was extracted with ether. The organic phase was washed with 1M Na2S203
and saturated NaHCO3 aqueous solutions, dried and rotovaped. The residue
was distilled to give ester 157 (38.4 g, 89%). A solution of ester 157 (20.0 g,
90.5 mmol) and distilled quinoline (17.1 mL, 145 mmol) was refluxed for 1 hour.
The mixture was cooled to room temperature, treated with 20% HCI (100 mL)
and extracted with ether. The organic extract was washed with 10% HCI, water
and saturated NaHCO3 (aq.). This extract was dried, rotovaped and
chromatographed to give 158 (12.6 g, 99%). Compound 158 (5.00 g, 35.8
mmol) was dissolved in benzene (50 mL) and stirred. To this solution was
dropwise added a mixture of Cr03 (10.0 g, 100 mmol) in acetic anhydride (25
mL) and glacial acetic acid (50 mL) over 30 minutes. After stirring for additional
20 minutes, benzene (50 mL) was added to dilute the reaction mixture. Chilled
by ice, this acidic mixture was slowly neutralized with saturated KOH aqueous
solution. The mixture was extracted with ether. The extract was washed with
water, dried, rotovaped and chromatographed to afford 159 (2.81 g, 52%) as a
clear oil. Rf (2:1 ether/hexane) 0.48. 1H NMR 5 6.73 (t, J=2 Hz, 1H), 3.84 (s, 3H),
2.60 (dt, J=6 Hz, 2 Hz, 2H), 2.46 (m, 2H), 2.07 (m, 2H); 13C NMR 8 199.6,166.8,
148.6, 132.9, 52.4, 37.5, 24.7, 22.0. HRMS for C8H1003, calcd: 154.0630.
Found: 154.0650.
6-Methoxvcarbonylbicvclof4.1.Olheptan-2-one (153). NaH (60%, 57 mg, 1.43
mmol) was placed in a 3-necked flask, washed with n-pentane (x3) and
pumped to dry. Trimethyloxosulfonium iodide (315 mg, 1.43 mmol) was added.
DMSO (2 mL) was dripped to the solid mixture through an additional funnel.







After hydrogen evolution, a milky solution turned clear and was stirred for 15
minutes. Compound 159 (200 mg, 1.30 mmol) in DMSO (1 mL) was added.
The mixture was stirred overnight and quenched with water. The mixture was
extracted with ether and the ether layer was dried, rotovaped, and
chromatographed to give 153 as an oil (76 mg, 35%). Rf(2:1 ether/hexane)
0.37. 1H NMR 8 3.71 (s, 3H), 2.39-2.17 (m, 4H), 2.13-2.01 (m, 1H), 1.87-1.79
(m, 1H), 1.72-1.67 (m, 1H), 1.64-1.54 (m, 2H); 13C NMR 8 205.3 (s), 173.0 (s),
52.1 (q), 36.4 (t), 33.6 (d), 28.7 (s), 22.3 (t), 18.0 (t), 16.7 (t). HRMS for C9H1203
M+H, calcd: 169.0865. Found: 169.0849.
5.5-Diphenylbicyclo[4.1.0lheptan-2-one (154). NaH (60%, 39 mg, 0.968 mmol)
was placed in a 3-necked flask, washed with n-pentane (x3) and pumped to dry.
Trimethyloxosulfonium iodide (213 mg, 0.968 mmol) was added. DMSO (2 mL)
was dripped to the solid mixture through an additional funnel. After hydrogen
evolution, a milky solution turned clear and was stirred for 15 minutes. 4,4-
Diphenyl-2-cyclohexen-l-one 160 (200 mg, 0.806 mmol) was added and the
mixture was stirred overnight. The reaction was quenched with water and
extracted with ether. The ether layer was dried, rotovaped and
chromatographed to give 154 as a white solid (171 mg, 81%). Rf (ether) 0.65.
IR (KBr) 1681; 1H NMR 8 7.38-7.17 (m, 10H), 2.55-2.42 (m, 1H), 2.33-2.11 (m,
4H), 1.89-1.76 (m, 1H), 1.41-1.35 (m, 1H), 1.21-1.13 (m, 1H); 13C NMR 8 207.3
(s), 148.3 (s), 146.3 (s), 128.3 (d), 128.2 (d), 127.7 (d), 126.7 (d), 126.4 (d),
126.2 (d), 44.5 (s), 33.5 (t), 28.5 (d), 27.9 (t), 27.6 (d), 10.0 (t). HRMS for
C19H180 M+H, calcd: 263.1436. Found: 263.1441.
Tricvclic ketone 155. NaH (60%, 320 mg, 8.00 mmol) was placed in a 3-necked
flask, washed with n-pentane (x3) and pumped to dry. Trimethyloxosulfoniumn
iodide (1760 mg, 8.00 mmol) was added. DMSO (10 mL) was dripped to the
solid mixture through an additional funnel. After hydrogen evolution, a milky







solution turned clear and was stirred for 15 minutes. (-)-Verbenone 161 (1000
mg, 6.67 mmol) in DMSO (5 mL) was added. This mixture was stirred for 24
hours. The reaction was quenched with water and extracted with ether. The
ether layer was dried, rotovaped and chromatographed to give 155 (1187 mg,
100%) as a clear oil. Rf (1:2 ether/hexane) 0.49; Rf (1:1 ether/hexane) 0.58. 1 H
NMR 8 2.26-2.21 (m, 1H), 2.19-2.14 (m, 2H), 1.61 (m, 1H), 1.48 (m, 1H), 1.32 (d,
J=1.2 Hz, 3H), 1.30 (m, 1H), 1.17 (d, J=1.2 Hz, 3H), 1.01 (d, J=0.9 Hz, 3H), 0.77
(m, 1H); 13C NMR 8 209.5, 57.8, 49.5, 45.4, 30.5, 26.0, 22.7, 22.0, 21.8, 21.7,
21.5. HRMS for Cl 1 Hi160 M+H, calcd: 165.1279. Found: 165.1300.
4-Methoxycarbonylcycloheptanone (165). A mixture of 153 (40 mg, 0.238
mmol), TBTH (192 p.L, 0.714 mmol) and AIBN (40 mg, 0.238 mmol) in benzene
(2.5 mL) was degassed by argon stream for 15 minutes. The mixture was
refluxed at 80C for 2 hours. Quenched with ethanol, the reaction mixture was
rotovaped and chromatographed to give 165 as an oil (28 mg, 69%). Rf (2:1
ether/hexane) 0.38. IR (KBr) 1734, 1700; 1H NMR 8 3.70 (s, 3H), 2.66-2.46 (m,
4H), 2.18-2.04 (m, 2H), 2.02-1.76 (m, 3H), 1.73-1.59 (m, 2H); 13C NMR 8 213.4
(s), 175.4 (s), 51.7 (q), 46.3 (d), 43.4 (t), 41.5 (t), 32.5 (t), 26.3 (t), 22.4 (t). These
NMR spectra were identical to those reported by Cossy.55
3-Methvyl-4.4-diphenylcyclohexanone (166). A mixture of 154 (84 mg, 0.321
immol), TBTH (173 giL, 0.642 mmol) and AIBN (53 mg, 0.321 mmol) in benzene
(3.2 mL) was degassed by argon stream for 15 minutes. The mixture was
refluxed at 80C for 2.5 hours. Quenched with ethanol, the reaction mixture was
rotovaped and chromatographed to give 166 as a white solid (73 mg, 86%). Rf
(ether) 0.71. 1H NMR 8 7.55-7.08 (m, 10H), 3.37-3.32 (m, 1H), 2.98-2.86 (m,
2H), 2.70 (m, 1H), 2.41-2.38 (m, 1H), 2.36-2.25 (m, 2H), 0.81 (d, J=7 Hz, 3H);
13C NMR 8 210.9 (s), 146.8 (s), 145.0 (s), 128.9 (d), 128.3 (d), 126.8 (d), 126.5

(d), 126.2 (d), 125.7 (d), 48.2 (s), 45.7 (t), 38.4 (t), 37.7 (d), 29.6 (t), 16.7 (q).







Anal. Calcd for C1 9H200: C, 86.31; H, 7.63. Found: C, 86.27; H, 7.85. HRMS
for C19H200 M+H, calcd: 265.1592. Found: 265.1598.
Bicyclic ketone 167. A mixture of ketone 155 (200 mg, 1.22 mmol), TBTH (656
gL, 2.44 mmol) and AIBN (80 mg, 0.49 mmol) in benzene (4 mL) was degassed
by argon stream for 15 minutes. The mixture was refluxed at 80C overnight.
Quenched with ethanol, the reaction mixture was rotovaped and
chromatographed to give 167 as a clear oil (86 mg, 76%). Rf (1:1 ether/hexane)
0.66. 1H NMR 8 2.54 (m, 2H), 2.37 (d, J=2 Hz, 2H), 1.88 (t, J=6 Hz, 1 H), 1.64 (d,
J=10 Hz, 1H), 1.36 (s, 3H), 1.19 (s, 3H), 1.09 (s, 3H), 1.02 (s, 3H); 13C NMR 8
214.5, 58.1, 53.6, 48.2, 41.1, 32.0, 31.8, 29.0, 27.2, 25.7, 25.4. HRMS for
Cl 1 H1i80, calcd: 166.1358. Found: 166.1366.
(Ethoxycarbonvlmethyl)triphenylphosphonium bromide (183). In an Erlenmeyer
flask, triphenylphosphine (131 g, 0.5 mol) was dissolved in benzene (250 mL).
This solution was stirred vigorously while ethyl bromoacetate (83.5 g, 0.5 mol)
was added dropwise. A white precipitate formed immediately. After 3 hours the
white precipitate was collected by a BUchner funnel and washed with cold
benzene (250 mL) and cold pentane (200 mL). The white solid then was
pumped overnight to dry. Compound 183 (213 g, 99.3% yield) was thus
obtained. 1H NMR 8 7.91-7.70 (m, 12H), 7.50-7.35 (m, 3H), 5.49 (m, 2H), 4.03
(m, 2H), 1.06 (m, 3H); 13C NMR 8 164.4, 135.1 (3C), 133.9 (3C), 133.8 (3C),
130.3 (3C), 130.1 (3C), 128.2 (3C), 117.824 (J31p-13C=-89 Hz for this doublet),
62.8, 33.1 (J31p-13C=57 Hz for this doublet), 13.6. HRMS for C22H2202P,
calcd: 349.1357. Found: 349.1358.
Ethyl allenecarboxylate (180).66 This synthetic work was identical to that
described by Lang and Hansen.66 In a 3-necked flask, Wittig salt 183 (30 g, 70
mmol) was dissolved in CH2CI2 (280 mL) at room temperature. To this flask a
solution of freshly distilled triethylamine (19.7 mL, 140 mmol) in CH2CI2 (70








mL) was added in 5 minutes with an additional funnel. Then the solution of
freshly distilled acetyl chloride (5.0 mL, 70 mmol) in 70 mL CH2CI2 was added
in 15 minutes. The reaction was monitored with TLC (stained in KMnO4-NaOH

aqueous solution). The reaction was completed in 1 hour. The reaction mixture
was rotovaped to remove CH2CI2. To the semi-solid residue was added 400
mL pentane. The slurry was then stirred for 2 hours. The precipitate was
removed by a Buchner funnel and the pentane filtrate was rotovaped to 50 mL
in volume. The precipitate was then again filtered with a Buchner funnel.
Distillation of the filtrate under reduced pressure afforded 180 (470 mg, 17%)
as colorless liquid, boiling point 82C at 9.5 torr. Rf (1:1 hexane/ ether) 0.66. 1H
NMR 8 5.64 (t, 1H), 5.22 (d, 2H), 4.21 (q, 2H), 1.29 (t, 3H); 13C NMR 8 215.6,

165.7, 88.0, 79.2, 60.9, 14.1.
2-Trimethvlsilvloxy-l1.3-cyclohexadiene (185).68 This synthetic work was
identical to that described by Rubottom and Grube.68 THF (240 mL) was placed
in a flask and chilled to -78C. To this flask was added diisopropylamine (13.6

g, 0.135 mol) and n-butyl lithium (2.5M in hexane, 58.8 mL, 0.147 mol). After 30
minutes, 2-cyclohexen-l-one 178 (12.0 g, 0.122 mol) was dropwise syringed
into the reaction flask over 5 minutes. After stirring at -78C for 20 minutes,

trimethylsilyl chloride (26.6 g, 0.245 mol) was added. The reaction mixture was
allowed to warm up to room temperature and stirred for 2 hours before it was
poured into an ice-cold stirred mixture of n-pentane (500 mL) and saturated
NaHCO3 aqueous solution (300 mL). After 10 minutes, the pentane phase was
quickly separated, dried with MgSO4, and rotovaped. Vacuum distillation of the
residue afforded 185 (18.0 g, 87%) as a clear liquid, boiling point 100C at 7.5
torr. IR (KBr) 3422, 1649, 1252, 1199. 1H NMR 8 5.96 (m, 1H), 5.79 (m, 1H),
4.98 (m, 1H), 2.28-2.17 (m, 4H), 0.29 (s, 9H); 13C NMR 5 148.1, 128.8, 126.5,

102.4, 22.6, 21.8, 0.2.