Title: Synthesis and reactivity in the cyclobutene series
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Title: Synthesis and reactivity in the cyclobutene series
Physical Description: v, 118 l. : illus. ; 28 cm.
Language: English
Creator: Burns, Michael Eugene, 1940-
Publication Date: 1966
Copyright Date: 1966
 Subjects
Subject: Cyclobutenes   ( lcsh )
Chemistry thesis Ph. D
Dissertations, Academic -- Chemistry -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Thesis: Thesis - University of Florida.
Bibliography: Bibliography: l. 111-117.
Additional Physical Form: Also available on World Wide Web
General Note: Manuscript copy.
General Note: Vita.
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Bibliographic ID: UF00097851
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000423940
oclc - 11034974
notis - ACH2345

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SYNTHESIS AND REACTIVITY IN THE

CYCLOBUTENE SERIES











By

MICHAEL EUGENE BURNS













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













UNIVERSITY OF FLORIDA
December, 1966











ACKNOWLEDGMENTS


The author is deeply indebted to his research

director, Dr. Merle A. Battiste, for his unrelenting

guidance, enthusiasm, and friendship.

Special recognition is due the author's parents

and immediate family for their constant interest,

encouragement, and support.

The author gratefully acknowledges his colleagues.

Their invaluable discussions, technical assistance, and

friendship are deeply appreciated.

The author expresses his thanks to Mrs. Thyra

Johnston for her excellent typing of the manuscript.

Acknowledgment is made to the Air Force Office of

Scientific Research, the National Science Foundation, and

the Graduate School of the University of Florida for

financial support.












TABLE OF CONTENTS

Page

ACKNOWLEDGENTS .. . . . . . . . . ii

LIST OF TABLES. . . . . . . . . . iv

LIST OF FIGURES . . . . . . . .. .. v

Chapter

I. DIELS-ALDER REACTI^S OF SUBSTITUTED
CYCLOBUTENES . . . .. . . .. 1

Introduction . .. . . . . 1

Results and Discussion . . . ... 9

II. STRUCTURE AND REACTIVITY OF DIPHENYLCYCLO-
BUTADIENOQUINONE HONOTOSYLHYDRAZONE. . 23

Introduction . . . . . . . 23

Results and Discussion . . . . . 25

III. THE SYNTHESIS AND VALENCE ISOMERIZATION OF
1,2-DIPHENYLCYCLOBUTENE. . . . .. 33

Introduction .. . . . . . 33

Results and Discussion . . . . .. 38

IV. EXPERIMENTAL. . . . . . . . . 61

V. SUMMARY . . .. .. . . . .. . 108

BIBLIOGRAPHY. .... . . . . . . ... 111

BIOGRAPHICAL SXETCH . . . . . . . .. 118


iii











LIST OF TABLES


Table

1. Rates of Isomerization of Methyl-Substituted
Cyclobutenes at 175 .

2. Rates of Isomerization of cis- and trans-
1,2,3,4-Tetraphenylcyclobutene at 175 0 .

3. Ultraviolet Maxima of Compounds Containing
the 1,2-Diphenylcyclobutene Chromophore .

4. Rate Constants for the Isomerization of
1,2-Diphenylcyclobutene in Isooctane .

5. Substituent Effects on the Kinetics of
Cyclobutene Valence Isomerization. . .


Page


S 35


S 38


S 41











LIST OF FIGURES


Figure Page

1. The ultraviolet spectra of cis- and trans-
stilbene67'68 and 1,2-diphenylcyclobutene. . 43

2. First-order kinetic plots for the thermal
isomerization of 1,2-diphenylcyclobutene in
isooctane (Run A) .. . . . . 50

3. First-order kinetic plots for the thermal
isomerization of 1,2-diphenylcyclobutene in
isooctane (Run B) . . . . . . 51

4. Arrhenius plot for the thermal isomerization
of 1,2-diphenylcyclobutene in isooctane. . 52











CHAPTER I


DIELS-ALDER REACTIONS OF SUBSTITUTED CYCLOBUTENES

Introduction


The continuing interest in non-benzenoid aromatic

compounds has resulted in a large number of significant

advances in this area.* Application of the synthetic

ingenuity of the organic chemist has yielded a variety of

systems suitable for testing the predictions of the LCAO MO

theory. Compounds which according -o molecular orbital

theory should possess appreciable aromatic character include

a number of cyclically conjugated charged-ring systems.

Monocyclic examples of these ring systems include the

cyclopropenyl cation, the cyclobutadienyl dianion and

dication, the cyclopentadienyl anion, the cycloheptatrienyl

cation, and the cyclooctatetraenyl dianion and dication.

Stable salts of derivatives of the cyclopropenyl

cation have been prepared and extensively studied by

Breslow and co-workers,5 although the parent ion is unknown.

The cyclobutadienyl dianion has not been observed to date

but a derivative of the benzocyclobutadienyl dianion has

been obtained by treatment of salt 1 with n-butyllithium


For reviews see references 1-4.







2
6
or lithium ethoxide. The bis-ylide 2 is reported to be


3P 3 Brr base 3

--r C -pz?3Br~ O f- _; 0
1 2


stable at -400 for at least several hours. The synthesis

of the dibenzocyclobutadienyl dianion has been claimed but
the interpretation and significance of the data has been
questioned.8 Farnum has reported the observation of a
carbonium ion which is possibly cyclobutadienyl dication 4,
although the evidence is not conclusive. The ion is formed

OH

r E2SOL
2 c
HO H

3
upon dissolution of a-bromoketone 3 in concentrated sulfuric

acid. A claim10 of the tetraphenylcyclobutadienyl dication

(5) has been withdrawn due to the results of an x-ray
investigation.12 A second reportll of an ion which could
be dication 5 appears more likely although again the data is
not beyond question, pointing out the extreme difficulty in
distinguishing between mono- and dication in this series.
The parent ions have been obtained in the cases of the







3


cyclopentadienyl anion and the cycloheptatrienyl cation.

In addition, a large number of stable salts (including inner

salts) of these two ions have been prepared and studied.*

The cyclooctatetraenyl dianion has been synthesized and

studied by Katz.13 The cyclooctatetraenyl dication and its

derivatives are unknown. Efforts to prepare this ion by

hydride abstraction from 1,3,5-cyclooctatriene, by reaction

of cyclooctatetraene dichloride with stannic chloride, or

by treatment of cyclooctatetraene with stannic bromide and

bromine were unsuccessful.14

A series of exceedingly interesting compounds is

composed of the carbonyl analogues of the positive ions

mentioned above. For example, the carbonyl analogue of

the cyclopropenyl cation is cyclopropenone (6a). Cyclo-

propenone should possess some degree of aromatic character

as a consequence of contributions to the resonance hybrid

by dipolar form 6b. Similar situations exist for cyclo-

butadienoquinone (?a and 7b), tropone (8a and 8b), and

cyclooctatetraenoquinone (9a and 9b or 10a and 10b).

0 0- 0 0



6a 6b a 7b

See references 1, 2 and 4 for reviews.











0 0O
II




8a 8b

0 0 0 O0






9a 9b 10a 10b


In good agreement with the theoretical predictions,

derivatives of cyclopropenone have been synthesized by a

variety of methods and exhibit the expected stability.15

Unsubstituted cyclopropenone is unknown and an attempted

synthesis by means of a route which afforded methylcyclo-
15a
propenone was unsuccessful.1 The first derivative of the

cyclobutadienoquinone ring system (7a) was prepared in 1955
16
by Smutny and Roberts. Cyclobutene 1i is converted to

phenylcyclobutadienoquinone (12) by 92 per cent sulfuric

acid at 1000. The unusual stability of 12 is evidenced by

its survival under the rather drastic conditions of its

preparation. Following this initial synthesis, reports of

a wide variety of derivatives of cyclobutadienoquinone have

appeared17 but the parent compound remains unknown. The







5
F
Cl-0 92% --
1 2 o/
IH2S04

11 12

chemistry of tropone and its derivatives has been well
established and indicates that the zwitterionic form 8b
makes a considerable contribution to the ground state.*
Neither the parent compounds nor any derivatives have been
synthesized in the cases of the cyclooctatetraenoquinones
9a and lOa.
The fact that the dipolar resonance forms can con-
tribute significantly to the stabilization of the carbonyl
derivatives mentioned above is dramatically demonstrated
in the instance of the cyclopropenone system. On the basis
of ring strain alone, one would predict that cyclopropanones

(13) would be more stable than cyclopropenones. Recent
work18 has shown that the reverse is actually the case.
Cyclopropanones readily undergo reactions which result in
relief of ring strain.

0
I


For a review see reference 4.










The lack of available data concerning the cycloocta-

tetraenyl dication makes the synthesis of this ion a very

desirable goal. The successful preparation13 of the cyclo-

octatetraenyl dianion suggests that the delocalization

energy of multicharged ions containing 4n+2 t-electrons may

be sufficient to overcome the destabilizing electrostatic

forces resulting from multiple positive or negative charges.

The marked stability of carbonyl compounds 6a-8a indicates

that a study of quinones 9a and 10a would provide informa-

tion concerning the possible aromaticity of the cycloocta-

tetraenyl dication in addition to serving as logical pre-

cursors for the synthesis of derivatives of this ion.

A conceivable synthesis of derivatives of quinone 9a

would involve entry into the cyclooctatriene ring system via

a Diels-Alder reaction between a fluorine-substituted

cyclobutene and a properly chosen diene. Chart I depicts

Chart I







SR R
RRrnF2 -C- O




1 F2 lF2 O


14 15 16









one such possible combination. Strong acid hydrolysis of

the resulting cyclooctatriene 14 2 15 could result in

quinone 16.

The work to be described in this chapter involves the

attempted synthesis of cyclooctatrienes of the type 1L = 15

by means of Diels-Alder reactions utilizing cyclobutene

derivatives as the dienophilic component.

Examples of the participation of cyclobutene or its

derivatives in the Diels-Alder reaction are not numerous.

Vogel19,20 has shown that cyclobutenes in which the double

bonds are substituted with activating carbomethoxy groups

are excellent dienophiles. Reaction of 1,2-dicarbomethoxy-

cyclobutene with butadiene leads to the bicyclic adduct 17,

which can be converted to cyclooctatriene 18 by treatment

with N-bromosuccinimide followed by elimination of hydrogen

bromide (Chart II).19 Shozda and Putnam21 found that

Chart II

CO2CH CO2CH3
S I 1)NBS
+ --- ---
2I .2)-HBr
CO2CH 02OCH
23 2










3,3,4,4-tetrafluorocyclobutene (19) reacts with dienes under

reasonably mild conditions. Adducts were obtained with

butadiene, 2,3-dimethylbutadiene, cyclopentadiene, furan,

and 2,5-dimethylfuran. Cyclobutene adds to the extremely

reactive 3,6-dicarbomethoxy-l,2,4,5-tetrazine to form an

adduct, resulting from loss of nitrogen, in 83 per cent
22
yield.2 cis-3,4-Dichlorocyclobutene reacts with 9,10-

dimethyl- and 9,10-dibromoanthracene to give normal Diels-

Alder adducts in high yield.23 The adduct from the dichloro-

cyclobutene and 9,10-dimethylanthracene was dechlorinated

to the corresponding cyclobutene derivative which also proved

to be a good dienophile. Studies of unsaturated four-

membered cyclic sulfones have shown them to be moderately
24
good dienophiles.2 The fact that fused cyclobutadiene
25
derivatives such as 20 react very readily with dienes25 can

not be considered informative regarding the dienophilic

properties of related cyclobutenes.

F2




19 20

For the purposes of comparison, the available
26
literature26 describing cyclopropenes as dienophiles is

somewhat more revealing. These compounds normally possess

high dienophilic reactivity except in the case of geminally









substituted cyclopropenes which are unreactive, apparently

for steric reasons.26d,e


Results and Discussion


A priori, the route to derivatives of the cyclo-

octatetraenoquinone ring system outlined in Chart I appeared

feasible- for a number of reasons. The fluorine-substituted

cyclobutenes which were to be used as dienophiles show the

remarkable thermal stability typical of fluorine-substituted
27
four-membered rings.27 This characteristic allows the use

of long reaction times and relatively high reaction tempera-

tures. Cyclobutenes in general should serve as reactive

dienophiles as a result of angular strain. This strain

should have a reaction promoting effect due to a reduction

in angular deformation in the transition state leading to

adduct formation. The reactivity of cyclopropene is not

seriously impaired by the presence of bulky vinylic sub-

stituents,26b,c,e and it appeared likely that this would

also be true for the cyclobutene series. Finally, the

observations of Shozda and Putnam21 with regards to the

dienophilic reactivity of 19 indicate that the presence of

four allylic fluorines on the cyclobutene ring does not

prevent this olefin from participating in the Diels-Alder

reaction.









The fluorocyclobutenes which were studied as possible

precursors to fluorine-substituted cyclooctatrienes were
1,2-diphenyltetrafluorocyclobutene (21), 1,2-dimethyltetra-

fluorocyclobutene (22), and 3,3,4,4-tetrafluorocyclobutene

(19). The reactivity of diphenylcyclobutadienoquinone (23)
was also studied since adduct formation with this cyclo-

butene could conceivably result in a one-step synthesis of

derivatives of 9a. In addition, some preliminary investi-

gations were conducted on 1,2-diphenylcyclobutene (24) as a
dienophile in order to gain some insight as to the factors

influencing dienophilic reactivity in the cyclobutene series.

F CH F2 /2

F 2 F2 2
CH /
21 22 23 24

The dienes selected were ones which have been shown

to give adducts with cyclopropenes. These dienes were

(reference is to the adduct with a cyclopropene) tetra-

phenylcyclopentadienone (tetracyclone) (25),26b 1,3-di-

phenylisobenzofuran (26),28 phencyclone (27),28 1,4-di-
phenyl-l,3-butadiene (28),29 a-pyrone (29),29 and 5,5-di-

methoxytetrachlorocyclopentadiene (30).28










0
-=0 0
=o

O2 2
2 26 27
Cl
C 0 OCH5



28 29 30

1,2-Diphenyltetrafluorocyclobutene (21)

Cyclobutene 21 was prepared by the method of Park50
involving the addition, elimination reaction of perfluoro-
cyclobutene (31) with phenylmagnesium bromide.


S + 20 MgBr 21

31
The reaction of 21 with tetracyclone (25) under what

are normally considered as forcing conditions for the Diels-
Alder reaction failed to yield any detectable adduct formation.
The lack of reaction was ascertained by the failure of the
cyclobutene to discharge the characteristic violet color of
25 and by recovery of unchanged cyclobutene by chromatography
(see Experimental Section). When mixtures of 21 and 25 were
fused at temperatures as high as 2950 the tetracyclone color
was not discharged and gas evolution did not occur. The










absence of gas evolution is significant since if the bridged

adduct 32 had been formed it would most likely have lost the

carbon monoxide bridge at these extreme temperatures. Other



F2
=0



32

attempts at adduct formation with 21 and 25 are described in

the Experimental Section.

The reaction of 1,3-diphenylisobenzofuran (26) with

excess 21 in refluxing toluene for three days or in re-

fluxing xylene for 29 days resulted in no Diels-Alder adduct

formation. These results indicate that little hope exists

for 21 as a dienophile since furan 26 is a very reactive

diene commonly used for the trapping of transient dieno-

philic intermediates. In agreement with this observation,

21 failed to add to phencyclone (27) (where the formation

of an additional aromatic nucleus in the product is a driving

force for reaction) or to 1,4-diphenyl-1,3-butadiene (28).

1,2-Dimethyltetrafluorocyclobutene (22)

Cyclobutene 22 was prepared by the reaction of methyl-

lithium with perfluorocyclobutene (31) as reported by

Blomquist and Vierling.7

Refluxing a neat mixture of cyclopentadiene 30 and

excess 22 for 9.5 days resulted in no isolable Diels-Alder









adduct. Similarly, refluxing a toluene solution of cyclo-

pentadienone 25 with a large excess of 1,2-dimethyltetra-

fluorocyclobutene (22) failed to discharge the violet color

of 25 and furnished no indication of Diels-Alder adduct

formation.

3, 3 4,4-Tetrafluorocyclobutene (19)31,52

As mentioned previously, cyclobutene 19 has been

shown to react with dienes in a normal manner to give Diels-
21
Alder products in reasonable yield. However, 19 failed

to react with a-pyrone (29) when a neat mixture of the two

was heated in a sealed tube at 60-750 for 30 days. Adduct

33 could have provided a route to the unsubstituted 1,2-
cyclooctatetraenoquinone (9a) via decarboxylation followed

by acid hydrolysis (Chart III).

Chart III

F2 -CO2 F29
29 + 19 -F -C F2
2 C 2

33
Heating a benzene solution of tetracyclone (25) and

excess 19 at 1000 for 25 days in a sealed tube failed to

discharge the violet color of the diene. Chromatography led

to the isolation of a trace of impure white solid which

turned violet at its melting point. The violet color very

likely indicates a retro-Diels-Alder reaction in which the









tetracyclone is regenerated. It is thus possible that this

material is in fact the bridged adduct 34 although insuf-

ficient material was obtained for characterization. It is

evident that the formation of 34 in reasonable yield will

require reaction temperatures in excess of 1000. Decarbony-

lation of 34 would provide a cyclooctatriene of structure



F 2
=0





suitable for conversion to a derivative of the 1,2-quinone

9a.

When a benzene solution of 1,3-diphenylisobenzofuran

(26) and excess 19 is heated in a sealed tube at 1000 for

15 days a 64 per cent yield of adduct 35 is obtained. The

structure of 35 was established by elemental analysis,

spectral data, and the apparent retro-Diels-Alder reaction

upon melting (see Experimental Section).




26 + 19 > F2
C F0 2










When heated at its melting point adduct 35 turns the bright-

fluorescent yellow characteristic of furan 26. Attempts at

conversion of 35 into a benzocyclooctatriene derivative by

removal of the oxygen bridge were unsuccessful. This com-

pound was resistant to deoxygenation with trimethylphosphite

or concentrated sulfuric acid, with both reactions affording

only unchanged starting material. Similarly, the adduct

(36) formed by reaction of 19 with furan has been shown to

be unreactive toward attempts at removal of the oxygen

bridge.33


F2



36

The investigation of the Diels-Alder reactions of 19

has not been satisfactorily completed due to a lack of

availability of this cyclobutene. The studies described

above indicate that the pertinent synthetic routes employing

19 as a dienophile may be feasible. In particular, the

reaction of 19 with tetracyclone is deserving of further

study.

1,2-Diphenylcyclobutene (24)

Initial studies of the Diels-Alder reactions of 24

indicate that it is not a good dienophile. Cyclobutene.241










fails to react with tetracyclone in refluxing benzene. 1,2-

Diphenylcyclobutene apparently forms an adduct with 1,3-di-

phenylisobenzofuran (26). However, the reaction is very

slow and the product has not yet been obtained in sufficient

yield and purity for full characterization. In contrast with
26e
the behavior of cyclopropene derivatives, cyclobutene 24

is not reduced by diimide.

The lack of dienophilic reactivity in cyclobutenes

21, 22 and 24 is somewhat surprising. The experiments des-

cribed above were designed with a synthetic goal in mind and

thus do not comprise a systematic study of the reactivity

of cyclobutenes in the Diels-Alder reaction. The paucity

of reported data concerning the use of cyclobutenes in the

diene synthesis makes the assessment of the precise reasons

for the observed inertness rather difficult. However, some

general observations can be made.

Two pertinent factors concerning the Diels-Alder

reaction are: a) the reactivity of the dienophile is

normally increased by electron-withdrawing groups, and b)

the reaction is very sensitive to steric factors. The

observed21 reactivity of 5,5,4,4-tetrafluorocyclobutene

indicates that the fluorine substituents have no deleterious

effect on the reactivity of the olefin although a direct

comparison with cyclobutene is not available. It is very

possible that the fluorines are actually serving to activate

the cyclobutene by means of electron withdrawal. It thus










seems that the principle cause of lack of dienophilic re-

activity in cyclobutenes 21 and 22 is a result of steric

effects due to the presence of two substituents on the

cyclobutene double bond. The steric factor takes on added

importance when one considers that the dienes employed in

the study of cyclobutenes 21 and 22 are all heavily substi-

tuted with bulky groups. The success of Vogel19,20 in

obtaining Diels-Alder adducts with 1-carbomethoxy- and 1,2-

dicarbomethoxycyclobutene may be ascribed to the fact that

the carbomethoxy group is an excellent dienophile activator.

In addition, the dienes used in these syntheses (butadiene,

1,4-dichloro-l,3-butadiene and a-pyrone) were ones having

relatively low degrees of substitution. A more complete

appraisal of the relative effects of the fluorine substitu-

ents and steric factors must await the accumulation of

additional data, particularly with regard to the reactivity

of 1,2-diphenylcyclobutene. In any case, it must be kept

in mind that a Diels-Alder reaction is composed of two

components, diene and dienophile. Reactivity is thus a

function of both elements and any comparison of dienophile

reactivities should be for reactions where the diene is of

constant or nearly constant structure.

The observed lack of reactivity of some of the cyclo-

butene derivatives described above prompts a comparison with

the cyclopropene series. As mentioned earlier, cyclopropenes










(except those which are geminally substituted) are active

dienophiles even when the double bond of the cyclopropene

bears two phenyl substituents. A comparison u' the two

small ring compounds necessitates a discussion of three

factors.

The first point involves the presence of ring strain

in the dienophile. The pronounced angular strain of the

cyclopropene ring3 is considerably decreased in the Diels-

Alder adduct where the three-membered ring has become

saturated. This reduction in strain is already present in

the transition state leading to adduct formation and thus

has an accelerating effect on the reaction. This effect is

less important in the cyclobutene series where angular

distortion is not as large.

The second point concerns steric factors stemming

from the orientation of substituents about the double bond

of the dienopnile. In 1,2-disubstituted cyclopropenes the

vinylic substituents can more readily achieve coplanarity

with the ring than can vinylic substituents in 1,2-di-

substituted cyclobutenes (see Chapter III for a more

detailed discussion of this point). while the ultraviolet

spectrum of 1,2-diphenylcyclobutene (see Chapter III)

indicates that the phenyl rings may be nearly coplanar with

the cyclobutene ring they will not be as coplanar as the

phenyl substituents in 1,2-diphenylcyclopropenes. While









this deviation in coplanarity in going from cyclopropene to

cyclobutene may be small, it could have a large effect on

the energy of the transition state for formation of the

Diels-Alder adduct by providing steric hindrance to the

approaching diene.

A third point relates to the electronic structure of

small-ring compounds. Several models have been proposed to

account for the stability, reactivity, and unusual bond

angles of the cyclopropane ring.35 It is possible that

some measure of the high reactivity of cyclopropenes as

compared to cyclobutenes in the diene synthesis is a result

of the electronic structure of the three-membered ring.

However, the precise nature and relative importance of this

effect, or even whether or not such an effect exists, can-

not be properly determined at this time. In addition,

there exists no firm basis for prediction of whether this

effect would be rate accelerating or rate retarding.

The factors discussed above provide a qualitative

explanation for the differing reactivities of cyclopropenes

and cyclobutenes. A determination of the relative impor-

tances of these factors will require a more detailed study.









Diphenylcyclobutadienoquinone (23)

Quinone 2_ was prepared by sulfuric acid hydrolysis

of 21 as described by Blomquist and LaLancette.17a The

possibility that 23 could enter into the Diels-Alder re-

action was investigated since adduct formation with this

quinone could result in a one-step synthesis of the cyclo-

octatetraenoquinone ring system.

Diphenylcyclobutadienoquinone failed to form an

adduct with furan 26 in refluxing benzene. Reaction with

tetracyclone in refluxing toluene or xylene was unsuc-

cessful. Fusing mixtures of 2_ and tetracyclone at

temperatures of approximately 2000 resulted in the evolu-

tion of small amounts of gas but afforded no isolable adduct.

The failure of 23 to add to the dienes described

above is not surprising. The data obtained for olefins 21

and 24 indicate that the presence of two vinylic phenyl

substituents seriously affects the reactivity of cyclobutene

derivatives. Furthermore, diphenylcyclopropenone (37a) does

not enter into Diels-Alder reactions28 although 1,2,3-tri-

phenylcyclopropene is an excellent dienophile.26b,c,e The

0 0

4 II <> (t' '


37b










inertness of 37a is probably due to the fact that the cyclo-

propenone is a resonance hybrid of forms 37a and 37b and

addition to the double bond would involve loss of the

aromatic system. Diphenylcyclobutadienoquinone would be

predicted to be unreactive for the same reason.

Cycloaddition routes

Diphenylcyclopropcnime (37a) reacts with 1-diethyl-

amino-1,3-butadiene (38) to yield, after the loss of the

elements of diethylamine, 2,7-diphenyltropone (39).36 This

1,4-addition reaction could proceed by concerted cyclo-

2t Et Et 3E


?7a -- =0 --


jj
38



addition or by Michael-type addition followed by ring

closure of the resulting dipolar species.36

Reaction of enamine 38 with diphenylcyclobutadieno-

quinone at room temperature resulted in immediate decomposi-

tion of the quinone and afforded no isolable product.

Repetition of -his experiment at -780 followed by warming to

room temperature gave the same result. Butadiene 38 and 1,2-
d2l1..y.rltetrafluorocyclobutene failed to react in refluxing

benzene.










The destruction of quinone 23 by enamine 38 is

undoubtedly due to attack on the cyclobutene ring by the

nucleophilic nitrogen.7 Replacement of the diethylamino

group of 38 with an acetoxy group yields a butadiene which

may also serve as a dipolarophile. However, reaction of

l-acetoxy-l,3-butadiene (40) with diphenylcyclobutadieno-

quinone in refluxing benzene yielded only unchangcu

quinone.
0
0-CCH-












CHAPTER II


STRUCTURE AND REACTIVITY 07 DIP::NYTLCYCLOBUTADIENOQUINONE
MONOTOSYLHYDRAZC .-

Introduction


Tosylhydrazone derivatives of carbonyl compounds have

proved to be valuable syntheGic intermediates. The tosyl-

hydrazones are precursors of the corresponding diazo

compounds which in turn may decompose to yield carbenes

(Chart IV). The products derived from such carbenes are very

Chart IV


\ Ts:L72, (1) base -N2 \
C = O C0 = NH TTs > C = -=--- C:
/ / (2) Ts- / 2 /

often the result of intramolecular reactions such as

insertion, ring expansion, ring contraction, and elimination.

For example, solution pyrolysis of the sodium salt of cyclo-

butanone tosylhydrazone (41) affords methylenecyclopropane

in 80 per cent yield.38 Cyclobutene (20%) and trace amounts


TNHTs
f Te NaOC o i
--z= + +


41


of butadiene are also obtained.







24

The monotosylhydrazone derivatives of a-diketones

are of interest since they may be converted to the corres-

ponding a-diazoketones which derive stability from resonance

structures employing the carbonyl group (42a and 42b).

These a-diazoketones undergo a number of reactions, being

0C = 0 CC -0

+ I +
CC=N=N C- N = N

42a 42b

decomposed by heat, light, and a variety of catalysts. One

very important reaction is the Wolff rearrangement9 where

decomposition of the diazoketone in the presence of water,

alcohols, or amines yields rearrangement products as shown

in Chart V.

Chart V






H R"OH 0NH




R R 0 R 0
\ \ II i \ II
CH- CO2H CH-C-OR CH- C -NR
/ 2 / / 2
R R R

In this chapter the monotosylhydrazone derivative of

diphenylcyclobutadienoquinone (23) has been studied with the









objective of generating the diazoketone and carbene derived

from this derivative.


Results ard Discussion


The monotosylhydrazone derivative of quinone 23 has

been reported by Blomquist and LaLancettel7a although the

only data listed in support of the assigned structure was a

correct elemental analysis. In view of results reported40

for the benzocyclobutadienoquinone system (43) it was felt

that proof of structure for this derivative was necessary.

Quinone 43 reacts normally with 2,4-dinitrophenylhydrazine

and o-phenylenediamine to give the bis-2,4-dinitrophenyl-
IO0a
hydrazone and quinoxaline, respectively. However, 43

fails to give normal carbonyl derivatives with hydroxylamine,

hydrazine, or p-toluenesulfonylhydrazine (tosylhydrazine).40b

The only products isolated from these reactions were those

resulting from cleavage of the four-membered ring. For

example, reaction of 43 with tosylhydrazine under neutral

conditions afforded 2-tosylphthalazone (44). Similarly,

monoketal 45 gave a normal tosylhydrazone derivative (46)

0
N O- Ts
+ TsXEN N-H2 I








but acid hydrolysis of this derivative yielded the rearranged

product 44.


0> 0-)
0- O Ts MNHH2 0 acid

\ 4Ts

45 46

The data described above, coupled with the fact that
41
both phenylcyclobutadienoquinone41 and diphenylcyclobuta-
37
dienoquinone react with o-phenylenediamine to give re-

arranged quinoxaline derivatives resulting from cleavage of

the four-membered ring, necessitated proof that 23 forms a

normal toslyhydrazone derivative.

Treatment of quinone 23 with one equivalent of

tosylhydrazine in acidic ethanol solution affords a bright-

yellow, crystalline product (47) in yields of approximately

80 per cent. The melting point agreed with that reportedly a

for the assumed monotosylhydrazone derivative. The infra-

red spectrum showed absorption bands at 3.15 (N-H) and

5.67 p (small ring C=0). The n.m.r. spectrum of 47 supported
a normal monotosylhydrazone structure. Resonances were

observed at 7 1.15 (broad singlet, N-H), 1.78-2.80 (complex

multiple, aromatic protons), and 7.58 (sharp singlet, CH3),

with area ratios of 1:14:3, respectively. Conclusive proof

that 47 is indeed a normal tosylhydrazone derivative was

obtained by sulfuric acid hydrolysis which regenerated

quinone 23 in 59 per cent yield.









The nitrogen proton of 47 appears at considerably

lower field in the n.m.r. spectrum than do the nitrogen

protons of the tosylhydrazone derivatives examined in

Chapter III (see Experimental Section). This low field

absorption provides further support for structure 47 since

it is very likely that the shift is due to intramolecular

hydrogen bonding.



N-Ts
H
0 0

47

Attempts to convert 47 into the bistosylhydrazone

derivative were unsuccessful (see Experimental Section).

Tosylhydrazone 47 is a reasonable precursor of

diazodiphenylcyclobutenone (48a), which in turn could serve

as a source of carbene 49. It is of interest that diazo-

ketone 48a would not be expected to achieve resonance

stabilization in the usual manner of a-diazoketones. The

resonance form utilizing the carbonyl group (48b) should

not be a major contributing forn since it requires a cyclo-

butadiene nucleus. However, diazoketone 48a may achieve

resonance stabilization as shown in form 48c. Cyclobutene

48a may thus be viewed formally as a derivative of the

cyclobutadienyl dication.








+ -
N= NNNN NJ-


4 0 vO O
48-b 48a -48c





= CO 2

> =C=O R OH 2

L~9 50a 51


Generation of carbene 49 under the conditions of the
Wolff rearrangement could provide a new source of cyclo-
propene derivatives (51) via the intermediate ketene 50a.
This ketene may be considered a derivative of methylene-
cyclopropene and might be sufficiently stable to permit
isolation due to contributions to the resonance hybrid by
form 50b.




0 C=O C=

50a 50o









The conversion of the monotosylhydrazones of cyclic
a-diketones to the corresponding a-diazoketones may be
'12
effected by treatment with aqueous sodium hydroxide2 or

more simply by chromatography of the tosylhydrazone on
basic alumina.3 The reaction involves the formation of
the tosylhydrazone anion followed by elimination of the
sulfinate anion to yield the neutral diazoketone.
When solutions of tosylhydrazone 47 in polar organic

solvents were treated with aqueous sodium hydroxide, tri-

ethylamine, or n-butyllithium the organic solution turned
an immediate dark red indicating formation of anion 52.
The intense red color of anion 52 is accounted for by the


NNi Ts N T NTs

( \ + + BH+


47 52

extended length of the conjugated system available for de-

localization of the electron pair. 1his delocalization can

take place as shown in resonance forms 52a-52c. Again,

Ts N= TTs s =_N=NTs
SZ o
'\0 < > If <


52c


52b


52a










resonance forms involving a cyclobutadiene nucleus are

avoided. Anion 52 proved to be exceedingly stable toward

elimination of sulfinate anion.

When 52 was generated in a two-phase mixture of

methylene chloride and aqueous sodium hydroxide (one

equivalent) the organic layer became an immediate dark red.

There was no visual change in the mixture after stirring at

room temperature for three hours. Aqueous work-up afforded

only the starting tosylhydrazone in 88 per cent recovery.

Treatment of a chloroform solution of 47 with excess tri-

ethylamine again led to formation of a dark-red color.

Addition of hexane caused precipitation of crystalline 47

(85% recovery). Attempted vacuum pyrolysis of the

lithium salt of 47 yielded only a black, carbonaceous

residue with no volatile products observed.

Tosylhydrazone 47 was incompletely soluble in an

aqueous sodium hydroxide solution (one equivalent). Stir-

ring at room temperature resulted in the formation of an

orange suspension. When stirring was stopped yellow solid

settled beneath a bright-red aqueous solution. After

stirring such a suspension at room temperature for six days

the color of the mixture had changed to yellow and when

stirring was stopped yellow solid settled beneath a color-

less aqueous solution. Extraction with chloroform gave

unchanged 47 (50% recovery) along with an intractable brown










gum. This brown gum showed infrared absorption at 4.74

microns characteristic of the diazo group42,45 but all

attempts at isolation of a pure material were unsuccessful.

Acidification of the aqueous layer followed by extraction

with chloroform gave a yellow, heat-sensitive solid which

was not characterized. The fact that although the

characteristic red color of the anion of 47 was no longer

present 50 per cent of the tosylhydrazone was recovered

indicates that the products formed stem from the reaction of

the tosylhydrazone with two equivalents of base.

Attempted preparation of diazodiphenylcyclobutenone

by chromatography of 47 on basic alumina was unsuccessful.

The alumina column turned bright orange when a solution of

the tosylhydrazone was added. This orange color traveled

the length of -he column but the eluants were yellow. Elu-

tion with chloroform until the eluants were colorless af-

forded only unchanged 47 (60% recovery). The alumina column

remained a light-orange color after the tosylhydrazone had

been completely eluted. The relatively low recovery of

tosylhydrazone from this simple operation is very possibly

due to a photolytic decomposition of the anion on the

portion of the alumina surface which was exposed to light.

Preliminary studies of the decomposition of the sodium

salt of 47 in aprotic media indicate that this will not be a

productive method for the generation and study of carbene 49.








32

Decomposition of salts of 47 by photolysis could prove to

be a more fruitful route.











CHAPTER III


THE SYNTHESIS AND VALENCE ISOMERIZATION
OF 1,2-DIPHENYLCYCLO3UTENE

Introduction


The thermal conversion of cyclobutenes to 1,3-

butadienes has received a great deal of attention in recent
46
years. The reaction is of interest for several reasons.

The stereospecificity of the valence isomerizations of

cyclobutenes containing allylic substituents has been

recognized for some time but theoretical grounds for the

observed results have been advanced only recently.47

Properly substituted cyclobutene derivatives provide a

convenient source of experimental data with which to confirm

the predictions of the Woodward-Hoffmann rules. In addition,

the cyclobutene-butadiene isomerization is an ideal system

with which to investigate subtle effects of substituents on

the transition state of a unimolecular reaction. Very

importantly from a kinetic viewpoint, cyclobutene isomeri-

zations are characteristically homogeneous, unaffected by

radical inhibitors, and free from side reactions; yielding

normally a single butadiene isomer. The thermal isomeriza-

tions proceed at readily measurable rates in the temperature

range of 25-2000, making kinetic studies of these systems

experimentally feasible.










A great deal of the previous work on cyclobutene

valence isomerizations has been qualitative in nature,

dealing mainly with the stereochemistry of the resulting

butadiene and occasionally with the relative ease of

isomerization of cis-trans pairs of 5,4-disubstituted

derivatives. More recently the importance of quantitative

kinetic data has been recognized and a number of reports of

results of this type have appeared.

The series of compounds which has been most com-

pletely studied is composed of the methyl-substituted

cyclobutenes. Table 1 shows the members of this series for

which kinetic data is available along with the rate constants
46
calculated for 1750. The data of Table 1 indicate that

vinylic methyl substituents decrease the rate of isomeriza-

tion. For example, 1-methyl- and 1,2-dimethylcyclobutene

(54 and 56) both react more slowly than does cyclobutene

(55). In addition, 1,5-dimethyl- and 1,4-dimethylcyclobutene

(57 and 58) both isomerize at a lower rate than does 3-

methylcyclobutene (55). The situation for allylic methyl

substituents is more complex. The addition of a single

allylic methyl group or two trans methyl groups in the 3 and

4 positions of the ring increases the rate of isomerization.

On the other hand, a comparison of 1,2-dimethyl- and cis-

1,2,3,4-tetramethylcyclobutene (56 and 60) indicates that

the substitution of two cis methyl groups has little effect
on the rate of isomerization.5
on the rate of isomerization.








TABLE 1
RATES OF ISOMERIZATICT OF METHYL-SUBSTITUTED
CYCLOBUTENES AT 1750


k x 10 k x 10
Cpd. (sec.-I) Ref. Cpd. (sec.-1) Ref.


D


5_
58


4.6


160


56




0.94




2.6




0.45


1.8


t


iri










The rate differences observed for the compounds

listed in Table 1 are probably due to a combination of steric

and electronic factors. The steric factors are for the most

part rate retarding and arise from increased methyl-methyl

and methyl-hydrogen repulsions in the transition state for

ring opening. These interactions can occur between two

vinylic substituents and between a vinylic and an allylic

substituent. In addition, the thermal ring opening of
47
cyclobutene derivatives is a conrotatory process and those

compounds where an allylic methyl group must rotate inward

will experience a steric deceleration of the rate of

isomerization. The electronic effects of the methyl sub-

stituents are not as clearly defined. A lengthening of the

ring double bond by stabilizing methyl substituents is in

agreement with the trends observed although a consideration

of steric interactions affords the same result and the

relative weights of these two factors is difficult to assess.

Methyl groups in allylic positions can be rate accelerating

due to stabilization in the transition state of the develop-

ing t-centers. However, this rate increase can be effectively

neutralized by the aforementioned steric repulsions. It is

of interest to note that the substituent effects observed in

Table 1 are fairly subtle, with the largest difference in

reactivity being a factor of ca. 350.










The data of Table 1 suggest that eclipsing strain in

the ground state does not significantly affect the rate at

which these cyclobutene derivatives undergo ring opening.

Thus, cis-1,2,3,4-tetramethylcyclobutene (60) reacts con-

siderably slower than does trans-1,2,3,4-tetramethylcyclo-

butene (59), and hexamethylcyclobutene (62) is slowest of

all. It thus seems that eclipsing effects in the ground

state, although present to some degree, are overwhelmed by

the electronic and steric effects operative in the transition

state.

In contrast with the fairly small differences in

reactivity observed for the methyl-substituted cyclobutenes,

the addition of phenyl substituents to the cyclobutene ring

may result in a much larger effect on the rate of isomeriza-

tion. Table 2 shows the rate constants at 1750 (calculated

from the data reported in reference 54) for the valence

isomerization of cis- and trans-1,2,3,4-tetraphenylcyclo-

butene (63 and 64). It is immediately evident from the data

in Table 2 that the four phenyl substituents of 63 and 64

have a much greater effect on the rate of ring opening as

compared to cyclobutene than was observed with any of the

methyl-substituted compounds listed in Table 1. This en-

hanced reactivity indicates that a study of other members of

the phenyl-substituted series may prove enlightening as to

the precise nature of the substituent effects operative in










TABLE 2

RATES OF ISOMERIZATION OF CIS- AND TRANS-
1,2,3,4-TETRAPHENYLCYCLOBUTENE AT 1750


k x 104

Cpd. (sec.- ) Ref.


40,000 54


63


80,000 54


64


thermal isomerization of cyclobutene derivatives. The

present chapter describes a kinetic study of another member

of this series, 1,2-diphenylcyclobutene.

Results and Discussion


Synthesis and structure of 1,2-diphenylcyclobutene

A convenient source of 1,2-diphenylcyclobutene (24)

was required not only for the study of the valence isomeri-

zation but also in connection with the Diels-Alder studies

described in Chapter I. The synthetic route utilized in

this work is outlined in Chart VI. Several other methods









Chart VI

0 OH

C Br LAH



65 66 67

STsNHRi2








68 2L

of preparation of this hydrocarbon have recently been re-

ported.55 The properties described below for 1,2-diphenyl-
cyclobutene are identical in all respects with those listed

by these workers. Reaction of l-cyano-l-phenylcyclopropane

(65)56 with phenylmagnesium bromide followed by hydrolysis
of the resulting ketimine salt gave 1-phenylcyclopropyl

phenyl ketone (66).57 Lithium hydride reduction of this

ketone afforded 1-phenylcyclopropyl phenyl carbinol (67) in

81 per cent yield. Treatment of 66 with excess tosylhydra-

zine in ethanol containing trace amounts of acetic acid

yielded tosylhydrazone 68 in yields of 66-71 per cent after

seven days at reflux. The structures of 67 and 68 were con-

firmed by spectral and analytical data (see Experimental









Section). The slow rate of formation of tosylhydrazone 68

is undoubtedly due to steric hindrance at the reaction site

as evidenced by the much faster rate of formation of the

tosylhydrazone derivative of 1-phenylcyclopropyl methyl

ketone (69) videe infra). Conversion of 68 to 1,2-diphenyl-

cyclobutene was effected by means of an aprotic-Bamford-

Stevens reaction.58 It has been previously demonstrated

that tosylhydrazone derivatives of cyclopropyl aldehydes and

ketones decompose under aprotic-Bamford-Stevens conditions

to yield cyclobutene derivatives by ring expansion.38'59

The base catalyzed decomposition of 68 in purified N-methyl-

2-pyrrolidone at 1200, using freshly prepared sodium

methoxide as the base, gave 1,2-diphenylcyclobutene in

yields of 66-76 per cent.

The n.m.r. spectrum of 24 is in agreement with the

assigned structure, showing a complex multiple centered

at T 2.58 and a sharp singlet at 7.24 in the area ratio of

2.4:1.0, respectively. The position of the allylic protons

compares favorably with the value of T 7.46 reported for
60
the allylic protons of cyclobutene. The ultraviolet
spectrum of 24 shows isooctane 227.5 mu (E 24,100), 236 sh.
spectrum of 2 shows max
(13,500), 297 (18,400), 307 sh. (17,500) and 322 inf.
(10,800). Table 3 lists other compounds containing the

1,2-diphenylcyclobutene chromophore which have been reported

in the literature. It can be seen that allylic substituents









TABLE 3
ULTRAVIOLET MAXIMA OF COMPOUNDS CONTAINING THE
1,2-DIPHENYLCYCLOBUTENE CHROMOPHORE
Skmax mi (E ) Ref.


'4,


227.5 (24,100)


297 (18,400)


295


228 (15,800)


224
230


(8,600)
(8,000)


292 (12,500)


293 (17,750)


303 (19,500)


220 (28,900)


294 (17,000)


305 (20,000)


238 (26,000)


H-- CH2Br

Br1 CH2Br


303 (19,500)



288 (19,500)


OH



OH

- OH

F
Ov_1 2
II ---2


62


17a


54,64


64,65


1 VF









have only relatively minor effects on the position and

intensity of the long-wavelength absorption band. All of

the long-wavelength maxima fall in the range 288-305 mm.

The observed maximum at 297 my for 1,2-diphenylcyclobutene

provides further support for the assigned structure.

Although structurally 1,2-diphenylcyclobutene re-

sembles cis-stilbene the ultraviolet spectra of the two

hydrocarbons are considerably different. It can be seen in

Figure 1 that the spectrum of 24 more closely resembles the

spectrum of trans-stilbene than that of cis-stilbene. This

resemblance is most notable in the position of the long-

wavelength absorption band and in the vibrational structure

of both the 227.5 and 297 my bands. The long-wavelength

band of trans-stilbene appears at 294 my (c 27,950) in

heptane.67 The spectrum of cis-stilbene (ethanol) shows
structureless absorption bands at 224 my (6 24,400) and 280

my (e 10,450).7 As is the case for cis-stilbene, the

short-wavelength band of 24 is more intense than the long-

wavelength band. However, the 297 my band of 24 is con-

siderably more intense than is the 280 my band of cis-

stilbene. The above bathochromic and hyperchromic shifts

observed in the ultraviolet spectrum of 24 as compared with

the spectrum of cis-stilbene, coupled with the similarities

in the spectra of 24 and trans-stilbene, are interpreted to

mean that the phenyl rings of 24 are nearly coplanar with the






43











/ \
\ i


\ I
20- \ i
I / \

2 / / \'

\ I I



x I \ I
/

\ "/ '\
I \ "
'I / "I.
10 .










200 250 300 350


Fig. 1.-The ultraviolet spectra of cis- and trans-
stilbene67,68 and 1,2-diphenylcyclobutene.










cyclobutene ring. It should be noted that the shifts ob-

served in the spectrum of 24 as compared with cis-stilbene

may be due in part to electronic effects resulting from the

angular strain present in the cyclobutene ring, although

these effects should be relatively small.

The above coplanarity of the phenyl rings in 24 is

made possible by the angular distortions present in the

strained cyclobutene ring. These distortions result in a

0-C=C bond angle which is larger than the corresponding

bond angle in cis-stilbene. In general, the smaller the

size of a cycloalkene ring containing three to six carbon

atoms the less steric crowding present between vinylic

substituents. 9'70

Further support for the above conclusion concerning

the planarity of 1,2-diphenylcyclobutene is provided by

the n.m.r. spectrum of 24, in which the aromatic protons

appear as a complex multiple centered at T 2.58. The

aromatic protons of trans-stilbene appear as a complex

multiple centered at 1 2.6 whereas the aromatic protons of

cis-stilbene appear as a sharp singlet at 2.82.71

Valence isomerization of 1,2-diphenylcyclobutene. Structure
of the product

The product of the thermal isomerization of 1,2-di-

phenylcyclobutene has been shown by chemical and spectral

means to be the expected 2,3-diphenyl-l,3-butadiene (70).









Crystalline 70 could not be isolated from pyrolyses of neat

samples of 24 due to extensive polymer formation in reactions

run for ca. five half-lives (see Experimental Section).

Later work demonstrated that 70 could probably be isolated

from pyrolyses conducted in dilute solution under the con-

ditions used for the kinetic study of the isomerization

videe infra). However, in view of the other data obtained,

an experiment of this type was not considered necessary.
Chemical proof of the structure of the isomerization

product was obtained as shown in Chart VII. Refluxing a

xylene solution of 24 for 26 hours (ca. 8.5 half-lives) in

the presence of an equivalent of p-benzoquinone afforded a
25 per cent yield of 6,7-diphenyl-4a,5,8,8a-tetrahydro-l,4-

naphthoquinone (71), m.p. 161-1630 (lit.72 m.p. 163).

Similarly, refluxing a xylene solution of 24 for 26 hours

in the presence of an equivalent of 1,4-naphthoquinone gave

a 52 per cent yield of 2,3-diphenyl-1,4,4a,9a-tetrahydro-
9,10-anthraquinone (72), m.p. 165-166.50 (lit.72 m.p. 175-

1760). Quinone 72 was further characterized by oxidation

to 2,5-diphenyl-9,10-anthraquinone (72), m.p. 211.5-212.50
(lit.72 m.p. 211-2120). Addition of bromine to a chloroform

solution of a sample 24 that had been heated at 1900 for

seven minutes (ca. three half-lives) afforded 1,4-dibromo-
2,5-diphenyl-2-butene (74) in 40 per cent yield, m.p. 148-
150.5 (lit.72 m.p. 145-147)











Chart VII


0
I I


0


SCH2Br


BrCH2 C4


74


[03


O I
0


0
II

0


I I
0


n JI,










Spectral proof of the structure of the isomerization

product was obtained by analysis of the ultraviolet and

n.m.r. spectra of pyrolysis mixtures. A neat sample of 24

was heated in an open tube at 1900 for three minutes (ca.

1.5 half-lives) and the n.m.r. spectrum of the resulting

material examined immediately. The appearance of an AB

quartet centered at 4.67 (J = 1.8 cps) indicated formation

of butadiene 70. A comparison of the relative areas of the

cyclobutene and butadiene methylene protons indicated that

54 per cent of the cyclobutene had undergone isomerization,

a value which is in agreement with the calculated half-life

at this temperature. Further spectral evidence for the

formation of 70 in pyrolyses of 24 was obtained from the

ultraviolet spectra of the infinity points determined in

connection with the kinetic studies. The spectra of these
75
infinity points were identical with that reported for 2,5-

diphenyl-l,5-butadiene. For example, pyrolysis of a 6 x 10-3

M n-propanol solution of 24 at 1400 for 48 hours (15.7 half-

lives) afforded a solution which had a single ultraviolet

maximum at 242 mu (E 18,000). Reported73 for 2,3-diphenyl-

1,5-butadiene: cyclohexane 245 mu (G 18,100). The quanti-
max
tative agreement of the above ultraviolet data indicates

that the thermal isomerization of 1,2-diphenylcyclobutene

affords 2,3-diphenyl-l,3-butadiene as the sole product.










Valence isomerization of 1,2-diphenylcyclobutene. Kinetics
of the reaction

The procedure used for the rate studies and the method

of treatment of the data obtained are described in the

Experimental Section.

Initial studies of the valence isomerization of 24

in decalin showed that the reaction is first-order and

afforded values for the rate constant, k, of 0.548 x 10-4
-1 -4 -1
sec. at 138.4 + 0.20 and 2.79 x 10 sec. at 155.1 +

0.20. It was considered desirable to determine the rate

constant and related values to a higher degree of accuracy.

The isomerization was thus studied in greater detail using

isooctane as the solvent. The decalin previously employed

had proved difficult to purify and caused a bathochromic

shift of the ultraviolet band of 24 used to follow the

isomerization. All values of the reaction parameters re-

ported here have been calculated from the rate constants

obtained in isooctane. These values are in good agreement

with those previously reported4 on the basis of the rate

constants in decalin.

The rate constants were determined in isooctane from

135-1500 in 5 intervals. Points were taken from time = 0

to time = 180 minutes in intervals of 30 minutes. Two

separate solutions of approximately equal concentration in

24 were prepared and the rate of isomerization at each of










the four temperatures studied for each solution. The data

obtained from a solution 5.91 x 10- M in 24 are labeled

Run A and the data obtained from a 6.11 x 10-3 M solution

are labeled Run B. Figures 2 and 3 show plots of log

(D,-D )/(D, -D) against time for Runs A and B, respectively.

The rate constants obtained from these plots are listed in

Table 4. A plot of log kave against 1/T (Figure 4) yields

the value of 33,400 cal./mole for the Arrhenius activation

energy, Ea, and the value of log A = 15.46 for the frequency

factor, A. The entropy of activation, AS is determined to

be +0.3 E.U. at 1500. The rate expression for the thermal

isomerization of 1,2-diphenylcyclobutene is then: k = A

exp(-Ea/RT) = 1013.46 exp(-33,400/RT) sec.-l


TABLE 4

RATE CONSTANTS FOR THE ISOMERIZATION OF 1,2-DIPHENYLCYCLO-
BUTENE IN ISOOCTANE


Temperature


k x 10' (sec. -)


oC + 0.1 Run A Run B kv
ave

135.0 0.568 0.373 0.371
140.0 0.613 0.645 0.629

145.0 0.983 1.005 0.994

150.0 1.60 1.62 1.61









O 150.00

145.0

0 140.00

Q 135.0


log "0o
D -D




0. 32







0.16







0-
0 18 36 54 72 90 108
Time (sec.) x 102

Fig. 2.-First-order kinetic plots for the thermal isomeri-
zation of 1,2-diphenylcyclobutene in isooctane (Run A).






0.80


0.6.







0.4

Dw -


e 150.0

145.0O

0 140.00

Q 135.0


log D, -D





0.32-








0.16-








S18 36 54 92 90
Time (sec.) x 102

Fig. 3.-First-order kinetic plots for the thermal
isomerization of 1,2-diphenylcyclobutene in
isooctane (Run B).
















-3.81.









-3.97-




log kave



-4.13-


I


2.55


-I.


I2.
2.39


2.47


1/T x 1
1/T x 103 2.43


Fig. 4.-Arrhenius plot for the thermal isomerization of
1,2-diphenylcyclobutene in isooctane.


-5.7-










The frequency factor, log A = 13.46, is normal for a

unimolecular reaction in which the entropy of activation is

approximately zero.75 The observed entropy of activation,

AS' = 0.3 E.U., is in agreement with that found for other

cyclobutene valence isomerizations. For example, for
1s/ 48
cyclobutene AS = -1.4 E.U., for trans-1,2,3,4-tetra-

methylcyclobutene AS/ 0, and for cis-l,2,3,4-tetra-

methylcyclobutene AS/ = 0.3 E.U.46

The rate constants of unimolecular reactions in which

there is no great change in polarity between reactant and

product are normally solvent independent.76'77 A study of

the rate of isomerization of 24 in n-propanol and in n-
-4 -1
propionitrile afforded the values kl400 = 0.657 x 10 sec.
-4 -1
and kl400 = 0.610 x 10 sec. respectively. These values

are within experimental error of the rate constants obtained

in isooctane (Table 4) and the valence isomerization of 24

is thus solvent independent. The rates of isomerization of
46 46 54 54
cyclobutenes 59, 60, 63 and 64 have also been shown

to be independent of the solvent used.

Table 5 lists the pertinent kinetic values for 1,2-

diphenylcyclobutene and related compounds. Although reaction

rates in solution are not strictly comparable to those in the

gas phase, unimolecular reactions of the type under considera-

tion here normally give closely agreeing results in the two

phases.76,77
















0
H
-0 0 CO



0 1

H oO ,
,-t 0

0 O H
q ow


MM O



0 ~rs r\ r




00
i-l
H co 0



N 0

H



MO ;

C)
0 0
0 X 0 0
S* 0 r-
E-4
0
o 00










m 0
0 0 0.. P


















0
*O
0
a-)t


-0 -0-


-r\
ON




0
0
LU\







0
0
0
O-





CH
O
O




r-u







Lf\
Go









co
0


,-j
Lf \




0
0
0
0
O





O
r-l





0
0
0






CH
H

r-t









CO










0
Lo
O


0


0
o
0
Lt
U-N


P4
0















Pk P






po
a






0 IdP
r a



















0d p0 0 0
* 0P















Sdd d
a)














P4 0 0 0 0 0
o So










oa aoo
( r a -l




-pd o n ar a


o

a,
0

r-
0
0l
E7


Ir


0
o










0
a

o


0


)Zi
ff










It is obvious from the data in Table 5 that the rate

of isomerization of 1,2-diphenylcyclobutene is essentially

the same as that of cyclobutene. As a consequence, the

greatly enhanced rates of isomerization of 63 and 64 as

compared to cyclobutene are due entirely to the presence of

allylic phenyl substituents. Even in the case of cis-

1,2,3,4-tetraphenylcyclobutene (63), where conrotatory ring

opening must result in the sterically hindered cis,trans-

1,2,3,4-tetraphenylbutadiene (75), the rate of isomerization

at 1500 is 3.5 x 103 greater than for cyclobutene.



63



75
The finding that 1,2-dimethylcyclobutene (56)

isomerizes at one-tenth the rate of cyclobutene has been

attributed to a lengthening of the ring double bond by

stabilizing methyl substituents, resulting in a decrease in

ring strain and thus a decrease in the rate of ring open-

ing.51 However, as mentioned previously, steric factors
will also be important here as the transition state for ring

opening will involve increased methyl-methyl and methyl-

hydrogen interactions. If steric repulsions in the transi-

tion state and lengthening of the ring double bond by

stabilizing substituents are the only factors operating one










would predict that 1,2-diphenylcyclobutene would isomerize

at a rate even slower than that of 56. It thus appears

that there must be an additional effect operative in the

isomerization of 24. At the present it seems most likely

that the vinylic phenyl substituents of 1,2-diphenylcyclo-

butene serve to stabilize the transition state for ring

opening by overlap with the developing double bonds. This

stabilization, although minor relative to the effects of

allylic phenyl substituents, is sufficiently large to

counterbalance both steric interactions in the transition

state and electronic stabilization of the ground state.

The normal A factors and relatively low activation

energies which are characteristic of the valence isomeriza-

tions of cyclobutene derivatives tend to rule out a transi-

tion state resembling a biradical.78 The simplest represen-

tation of the transition state for ring opening involves a

planar arrangement of the four carbon atoms of the ring with

stabilization of the developing n-centers by the ring double

bond (76). It has been pointed out52'78 that a skew arrange-

ment (77) of the four ring carbon atoms is more favorable

since it allows a greater degree of overlap between the ring

double bond and the incipient n-centers. In addition, the

skew arrangement allows the greatest amount of overlap be-

tween the orbitals being formed by rupture of the C-bond,65'79














76 77

and is also the most favorable array for minimization of

steric repulsions. Recent work has provided experimental

support for the skew transition state. Freedman65'79 has

shown that room temperature solutions of butadienes 78 and

79, which exist in a cisoid-skew conformation (82) for
80
steric reasons, consist of an equilibrium mixture of the

butadienes and the corresponding cyclobutenes (80 and 81).

X







78, X=Br 80, X=Br
79, X=Cl 81, x=cl









The facile thermal conversion of butadienes to cyclobutenes

is normally observed only for fluorine-containing deriva-

tives.27 The ease with which butadienes 78 and 79 are

converted to the corresponding cyclobutenes is due to the

fact that the ground state conformation of the dienes (82)

is very similar to that proposed for the transition state

(77) for ring opening and ring closure.

The observed rate of isomerization of 1,2-diphenyl-

cyclobutene is also compatible with a skew transition state.

In a planar transition state (76) phenyl-phenyl and phenyl-

hydrogen interactions increase significantly as the 3,4-bond

of the ring ruptures and overlap between the phenyl rings

and the developing double bonds is hindered. However, in a

skew transition state (77) the phenyl rings are twisted out

of plane with one another and can thus effectively stabilize

the incipient double bonds.

The small pre-exponential factor found for the

isomerization of trans-1,2,3,4-tetraphenylcyclobutene indi-

cates a negative entropy of activation which is consistent

with extensive phenyl stabilization of developing x-centers

in the transition state.81

l-Phenylcyclobutene (83)

Attempts to study the rate of valence isomerization

of 1-phenylcyclobutene (83) have thus far been unsuccessful

due to the high tendency of this compound to polymerize.









The thermal isomerization of 83 was observed in the heated

injector chamber of a gas chromatograph. The product of

the isomerization was identified as the expected 2-phenyl-

1,3-butadiene (84) by a comparison of its retention time

with that of a known sample. The extent of valence isomeri-

zation at various injector port temperatures is described

in the Experimental Section.

l-Methyl-2-phenylcyclobutene (85)

An attempt was made to prepare the unknown 1-methyl-

2-phenylcyclobutene (85) by using a reaction scheme analogous

to that employed for 1,2-diphenylcyclobutene. Treatment of

1-phenylcyclopropyl methyl ketone (86)57a with tosylhydrazine

in glacial acetic acid at room temperature afforded tosyl-

hydrazone 69 in 77 per cent yield. The thermal decomposition

of the sodium salt of 69 appeared to proceed at a much

slower rate than did the decomposition of the corresponding

0 NNhHTs
CCH3 TsNHNH2 CCH NaOCH CH(?




86 69 85

salt of 68. V.p.c. analysis of the product of this reaction

showed five major components and at least seven minor compo-

nents (see Experimental Section). Spectral data indicated

that 85 was very likely present in the reaction product but

isolation of this material was not achieved.












CHAPTER IV


EXPERIMENTAL


General.-Melting points were determined on a Thomas-

Hoover capillary melting point apparatus. All melting and

boiling points are uncorrected. Elemental analyses were

performed by Galbraith Laboratories, Inc., Knoxville,

Tennessee. Analytical vapor phase chromatography was per-

formed using helium as the carrier gas with an Aerograph

Model 600-D Hy-Fi instrument (Wilkens) equipped with a

hydrogen flame ionization detector. All v.p.c. analyses

were performed on ether solutions and retention times are

reported relative to the ether peak.

Spectra.-Infrared spectra were recorded on either a

Perkin-Elmer Infracord spectrophotometer or with a Beckman

IR10 instrument. Ultraviolet and visible spectra were

determined on a Cary 14 recording spectrophotometer.

Nuclear magnetic resonance spectra were obtained with Varian

4300-2 and A-60A instruments. Tetramethylsilane was used

as an internal reference and chemical shifts are reported in

tau values.

1,2-Diphenyltetrafluorocyclobutene (21).17a'30'82

A solution of phenylmagnesium bromide was prepared under an










argon atmosphere from 13.4 g. (0.552 g.-atom) of magnesium

and 91.0 g. (0.580 mole) of bromobenzene in 250 ml. of

absolute ether. The water-cooled condenser used in the

preparation of the Grignard reagent was exchanged for a

dry-ice condenser and the ether solution cooled to 00.

Perfluorocyclobutene (31) (Peninsular ChemResearch, Inc.)

(55.8 g.; 0.221 mole) was bubbled into the ether solution
over a period of two hours. The reaction mixture was then

maintained at 00 for 2 hours, at room temperature for 3

hours, and at reflux for 30 minutes. The mixture was cooled

to 00 and 100 ml. of 10 per cent hydrochloric acid added

with care. The ether layer was separated and the aqueous

layer extracted with ether. The combined ether solutions

were washed with 5 per cent sodium bicarbonate solution and

saturated saline solution. After drying over sodium sulfate

the ether was removed on a rotary evaporator yielding a red

oil. 1-Phenylpentafluorocyclobutene was removed by distil-

lation [b.p. 660 (15 mm.), n 21 1.4639 (lit.30 b.p. 67-680/

15 mm., n25 1.4606)]; the infrared spectrum (neat) showed a

strong absorption for the fluorine-substituted double bond

at 5.85 microns. The residue from the distillation was

filtered through 400 g. of alumina (Merck 71707) using hexane

as the eluant. Removal of the solvent from the eluate (600

ml.) afforded a colorless oil. Crystallization from hexane









gave 16.34 g.(27%) of 1,2-diphenyltetrafluorocyclobutene as

colorless crystals, m.p. 56.5-580 (lit.17a,50,82 m.p. 580).

Attempted reaction of 1,2-diphenyltetrafluorocyclo-

butene (21) with tetraphenylcyclopentadienone (25).-The

reaction of 21 with cyclopentadienone 25 under a variety of

experimental conditions failed to yield any detectable Diels-

Alder product. These reactions are briefly summarized below.

A. Refluxing 25 with a 1.20 mole excess of cyclobutene

21 in xylene for 20 days failed to discharge the character-

istic violet color of 25. The only isolable materials were

unchanged 21 and 25.

B. A mixture of 25 and a 1.20 mole excess of 21 was

heated in a Wood's metal bath. The temperature of the bath

was raised from room temperature to 2250 over a two hour

period, maintained at 2250 for 3 hours, and then heated to

and maintained at 2950 over a period of 5 hours. Gas evolu-

tion was not observed and the violet color of the tetra-

cyclone was still present when the reaction was discontinued.

C. Refluxing 25 with a 4.0 mole excess of 21 in

1,2,4-trimethylbenzene for 12 days resulted only in the

decomposition of the tetracyclone. The only material

isolated was unchanged 21.

Attempted reaction of 1,2-diDhenyltetrafluorocyclo-

butene (21) with 1,3-diphenylisobenzofuran (26).

A. Refluxing 26 with a 1.04 mole excess of 21 in

toluene for 3 days failed to discharge the fluorescent-









yellow color of the furan and resulted in no detectable

adduct formation.

B. Refluxing 26 with a 1.03 mole excess of 21 in

xylene for 29 days yielded no evidence for formation of a

Diels-Alder adduct. In addition to starting materials, 0-

dibenzoylbenzene, the product of air oxidation of 26, was

isolated in 20 per cent yield (based on furan 26), m.p.

145-1470 (lit.83 m.p. 146-1470). The infrared spectrum

(KBr) of this material showed strong carbonyl stretching

absorption at 6.03 ) (lit.84 carbonyl absorption at 6.05 )).

Attempted reaction of 1,2-diphenyltetrafluorocyclo-

butene (21) with phencyclone (27).-A mixture of 21 (0.222 g.;

0.798 mmole) and phencyclone (0.264 g.; 0.691 mmole) in 12

ml.. of xylene was refluxed for 6.5 days. Over this period

of time the dark-green color of the phencyclone gradually

faded until the color of the xylene solution was yellow.

Chromatography on alumina (Merck 71707) using hexane as the

eluant resulted in the recovery of 0.199 g. (90%) of un-

changed 21. The nature of the products) formed by

decomposition of the phencyclone was not investigated.

Attempted reaction of 1,2-diphenyltetrafluorocyclo-

butene (21) with 1,4-diohenyl-1,5-butadiene (28).-A mixture

of 21 (0.167 g.; 0.601 mmole) and 1,4-diphenyl-1,3-butadiene

(0.124 g.; 0.602 mmole) in 10 ml. of xylene was refluxed for

20 days. The xylene solution was concentrated to a volume









of 3 ml. and ether added. Cooling afforded 0.064 g. (52%

recovery) of unchanged 28 which was identified by a compari-

son of melting point and infrared spectrum with that of a

known sample.

1,2-Dimethyltetrafluorocyclobutene (22).17b A solu-

tion of methyllithium was prepared under an argon atmosphere

from 10.6 g. (1.53 g.-atoms) of lithium wire and 116 g.

(0.817 mole) of methyl iodide in 325 ml. of dry ether. The

water-cooled condenser used during the preparation of the

lithium reagent was exchanged for a dry-ice condenser and

the ether solution cooled to -36 in a dry ice-ethylene

dichloride bath. Perfluorocyclobutene (31) (40 g.; 0.25

mole) was bubbled into the ether solution over a period of

30 minutes. The reaction mixture turned grey and finally

dark green by the time the addition was complete. The solu-

tion was stirred at -360 for 4 hours, at 0 for 2 hours, and

at room temperature for 17 hours. The mixture was cooled to

0 and carefully decomposed by addition of 150 ml. of 10 per

cent hydrochloric acid. The ether layer was separated and

the aqueous layer extracted with ether. The combined ether

solutions were washed with 5 per cent sodium bicarbonate

solution and saturated saline solution. After drying over

sodium sulfate the ether was removed by slow distillation.

Distillation of the black residue under argon at atmospheric

pressure gave 16.5 g. (43%) of 1,2-dimethyltetrafluorocyclo-
22 17b 27.5
butene, b.p. 97-980, n2 1.3493 (lit.1 b.p. 100-104, n75

1.3478).









The infrared spectrum (neat) showed absorption bands

at 6.95 (m), 7.17 (m), 7.24 (m), 7.48 (s), 8.25 (s), 9.12

(s), 9.72 (s), 10.86 (s), and 11.57 (m) U.

The material prepared above was obtained as a pink

liquid. This color was changed to brown by exposure to air

or by addition of acetone, but did not change when the

product was stored in a stoppered flask. In an attempt to

remove this pink color the material was filtered through a

column of alumina (Merck 71707) using petroleum ether (b.p.

20-40) as the eluant. The pink color was removed leaving

a black band at the top of the alumina column. The eluate

was initially colorless but turned pink upon standing for

three hours. Removal of the petroleum ether and distil-

lation of the residue under argon at atmospheric pressure

gave 22 as a pale-pink liquid. The pink color of this

material was not nearly as intense as was the color of the

initial product. It appears that the pink color is due to

the decomposition of a trace impurity.

Attempted reaction of 1,2-dimethyltetrafluorocyclo-

butene (22) with 5,5-dimethoxytetrachlorocycloDentadiene

(30).-A mixture of 2.844 g. (18.5 mmoles) of 22 and 1.033 g.

(3.91 mmoles) of freshly distilled (b.p. 950/2.5 mm.) 5,5-
85
dimethoxytetrachlorocyclopentadiene85 was heated at the

reflux temperature of the cyclobutene (bath temperature









1250) for 9.5 days. The infrared spectrum (neat) of the

resulting amber oil showed only those absorption bands which

are contained in the spectra of the starting materials.

The cyclobutene was removed by warming under a stream of

argon. The infrared spectrum of the resulting oil was

identical with that of an authentic sample of 30.

Attempted reaction of 1,2-dimethyltetrafluorocyclo-

butene (22) with tetraphenylcyclopentadienone (25).-A sus-

pension of 0.315 g. (0.842 mmole) of tetracyclone in 3.264

g. (21.2 mmoles) of 22 was heated under an argon atmosphere

at the reflux temperature of the cyclobutene (bath tempera-

ture 1250) for 15 hours. At the end of this time the

tetracyclone had crystallized on the sides of the reaction

flask and the cyclobutene remained as a clear, colorless

liquid. Toluene (4 ml.) was added and the resulting solu-

tion refluxed an additional 205 hours (total reaction time

220 hours). The resulting solution still retained the dark

violet color of the tetracyclone. Alumina chromatography

gave only unchanged 25.

Attempted reaction of 3,3,4,4-tetrafluorocyclobutene

(19)31 with c-pyrone (29).-A mixture of 19 (2.000 g.; 15.9
mmoles) and a-pyrone (1.430 g.; 14.9 mmoles) was heated in a

sealed tube for 18 days at 600 and for an additional 12 days

at 75. Alumina chromatography of the reaction mixture

afforded unchanged a-pyrone as the only isolable material

(no attempt was made to recover the low boiling cyclobutene).









Reaction of 3,3,4,4-tetrafluorocyclobutene (19) with

tetraohenylcyclopentadienone (25).-A mixture of 19 (1.00 g.;

7.93 mmoles) and tetracyclone (0.703 g.; 1.83 mmoles) dis-

solved in 5 ml. benzene was heated in a sealed tube at 1000.

The hot benzene solution contained a considerable amount of

undissolved tetracyclone. After 23 days at 1000 the appear-

ance of the mixture had not changed and the reaction was

discontinued. The reaction mixture was chromatographed on

a column of alumina (Merck 71707) packed in hexane. Elution

with mixtures of benzene-hexane gave a trace of white solid

(contaminated with tetracyclone) which eluted prior to the

tetracyclone. This material had m.p. 152-2100 (melt violet)
but was obtained in insufficient quantity for characteriza-

tion. The only other material isolated was unchanged 25.

Reaction of 3,3,4,4-tetrafluorocyclobutene (19) with

1,3-diphenylisobenzofuran (26).-A mixture of (19) (1.00 g.;

7.93 mmoles) and 1,3-diphenylisobenzofuran (0.631 g.; 2.34
mmoles) dissolved in 5 ml. of benzene was heated in a sealed

tube at 1000 for 15 days. Addition of ether to the resulting

benzene solution gave 0.595 g. (64%) of the Diels-Alder

adduct 35, m.p. 175-1980 (melt bright yellow). Two re-

crystallizations from benzene-hexane gave the analytical

sample, m.p. 197-199.
Anal. Calcd. for C24H16F40: C, 72.72; H, 4.07.

Found: C, 72.96; H, 4.24.









The infrared spectrum (KBr) showed absorption bands

at 3.25 (m), 6.26 (m), 6.68 (m), 6.85 (s), 7.40 (s), 7.65

(s), 7.88 (m), 8.04 (s), 8.40 (s), 8.63 (m), 8.95 (s), 9.03

(s), 9.13 (s), 9.48 (m), 10.00 (s), 10.40 (m), 10.62 (m),
10.77 (m), 11.02 (w), 11.16 (m), 11.44 (m), 11.86 (m), 12.52

(s), 12.88 (s), 13.27 (s), 13.44 (s), 14.30 sh. (s), 14.40

(s), and 14.78 (s) p.
The n.m.r. spectrum (CDC1 ) showed a complex multiple

at T 2.18-3.23 (aromatic protons) and a broad multiple at

6.17-6.70 (methine protons), with an area ratio of 14.0:2.18,

respectively.

The product with m.p. 175-1980 obtained above is

possibly a mixture of the exo and endo isomers. A small

amount of material with m.p. 155-1590 (melt bright yellow)

was isolated from this product as white needles. The pre-

dominant product (m.p. 197-1990) formed hard white crystals.

The Diels-Alder reaction of 19 with cyclopentadiene affords
21
a 1:1 mixture of the exo and endo isomers.21 The reaction

of 19 with furan affords only a single isomer.21 The prob-

lem of stereochemistry in the present system was not further
investigated.

Attempted deoxygenation of 35 with trimethyl phos-
phite.-A mixture of 96 mg. (0.242 mmole) of adduct 35 and

188 mg. (1.52 mmoles) of trimethyl phosphite dissolved in

2 ml. of benzene was refluxed for 24 hours. Addition of









petroleum ether (b.p. 30-600) to the cooled benzene solution

gave 80 mg. (83% recovery) of unchanged 35.

Attempted sulfuric acid hydrolysis of 35.-To 3 ml. of
hot (1000) concentrated sulfuric acid was added 97 mg.

(0.245 mmole) of 35. The resulting suspension was stirred

at 1000 for 1.5 hours. The mixture was poured onto ice and

the organic materials extracted into chloroform. The
chloroform solution was dried over sodium sulfate and

concentrated on a rotary evaporator. Addition of hexane

gave 65 mg. (67% recovery) of unchanged 35.

Attempted reaction of 1,2-diohenylcyclobutene (24)

with tetraphenylcyclopentadienone (25).-A benzene solution

of 1,2-diphenylcyclobutene (0.018 g.; 0.0875 mmole) and

tetraphenylcyclopentadienone (0.027 g.; 0.0702 mmole) was

heated at reflux for 5 days. At the end of this period the

characteristic dark-violet color of the tetracyclone had

not decreased in intensity. No attempt was made to recover

starting materials.

Attempted diimide reduction of 1,2-diphenylcyclo-

butene (24).86 To a stirred solution of 1,2-diphenylcyclo-

butene (0.250 g.; 1.21 mmoles) in 25 ml. of 1:1 dimethoxy-

ethane (freshly distilled)-methanol was added 0.469 g. (2.42

mmoles) of freshly prepared potassium azodicarboxylate.87

The reaction was carried out under an argon atmosphere. To

this stirred suspension was added 0.5 ml. of glacial acetic









acid over a period of 10 minutes. Stirring at room tempera-

ture for 4.5 hours resulted in a clear colorless solution.

This solution was poured into 40 ml. of water and the re-

sulting oil extracted into 75 ml. of hexane. The hexane

solution was washed with three 25 ml. portions of water,

separated, and dried over sodium sulfate. Removal of the

solvent on a rotary evaporator yielded a colorless oil which

crystallized from methanol at -780 to give 0.226 g. (90%

recovery) of unchanged 24 which was identified by its melting

point, mixed melting point with an authentic sample, and

qualitative ultraviolet spectrum.

Diphenylcyclobutadienoquinone (23).-The procedure

followed was that described by Blomquist and LaLancette.17a

In a typical preparation, an etched flask was heated to 1000

and then charged with 20 ml. of 96 per cent sulfuric acid.

1,2-Diphenyltetrafluorocyclobutene (21) (4.66 g.; 16.8

mmoles) was added in one portion. Copious evolution of

hydrogen fluoride began immediately. After stirring at 1000

for 30 minutes the mixture was poured onto ice and the

organic materials extracted into chloroform. The chloroform

solution was washed with water and dried over magnesium

sulfate. Removal of the solvent on a rotary evaporator gave

a yellow oil which crystallized from chloroform-hexane to

give 2.61 g. (67%) of quinone 23 as bright-yellow plates or

needles, m.p. 95-98.50. Recrystallization from chloroform-








hexane raises the melting point to 97-98.50 (lit.7a m.p.

97-97.20).
The infrared (KBr) and ultraviolet acetonitrilee)

spectra of this material were identical with those reported

in reference 17a. The n.m.r. spectrum (CDC13) showed only

aromatic protons as two multiplets centered at T 1.91 and

2.41.

Attempted reaction of diphenylcyclobutadienoquinone

(23) with 1,3-diphenylisobenzofuran (26).-An equimolar
mixture of 23 and furan 26 dissolved in benzene was re-

fluxed for 52 hours. Addition of ether to the cooled

benzene solution resulted only in the isolation of unchanged

starting materials.

Attempted reaction of diphenylcyclobutadienoquinone

(23) with tetraphenylcyclopentadienone (25).-Attempts to
obtain a Diels-Alder adduct by reaction of quinone 23 with

tetracyclone were unsuccessful. The various experiments

performed are summarized briefly below.

A. Refluxing 25 with a 1.4 mole excess of quinone 23

in xylene for 5 days resulted in no adduct formation.

Concentrating and cooling the xylene solution caused the

precipitation of unchanged tetracyclone. Trituration of

this material with chloroform gave trace amounts of a very

insoluble yellow solid with m.p. > 3000. Elemental analysis

of this yellow solid gave: C, 79.85; H, 4.61. The










possibility that this compound is the photodimer mentioned

by Blomquist and LaLancette7 was not investigated.
B. Refluxing 25 with a 1.4 mole excess of quinone

23 in toluene for 19 days failed to yield any detectable

Diels-Alder adduct. In addition to starting materials, very

small amounts of the yellow solid described in A were

isolated.

C. A solid mixture of 25 and a 2.0 mole excess of

quinone 23 was fused at 2100 for 5 minutes. The molten

mixture evolved a very small amount of gas but evolution

ceased within 5 minutes and the tetracyclone color was not

discharged. Workup gave only unchanged starting materials.

D. A Pyrex test tube containing a solid mixture of

tetracyclone and a 1.5 mole excess of quinone 23 was im-

mersed in a Wood's metal bath. The bath temperature was

initially 750 and was raised slowly over a period of 3

hours to 2250. At 200-2050 evolution of small amounts of

gas was observed. The temperature was maintained at 2250

for an additional 1.5 hours. At the end of this time the

violet color of the tetracyclone had not been discharged.

Examination of the mixture resulted only in the recovery of

unchanged starting materials.

1-Diethylanino-1,5-butadiene (58).-The procedure

followed was as described by Hiinig and Kahanek.88 Distil-

lation of the crude reaction mixture on a spinning-band









column gave enamine 38 as a light-yellow oil in 42 per cent
21 88
yield, b.p. 55-620 (12 mm.), n1 1.5258 (lit.8 b.p. 64-660/
10 mm., lit.89 nD1 1.5239). The infrared spectrum (neat)

showed strong absorption bands at 6.15, 10.08 and 18.84 p

(lit.89 strong absorption bands at 6.10, 10.14 and 10.95 p).

The identity of the product obtained above was further

demonstrated by its condensation with diphenylcyclopropenone

(57a) in refluxing benzene to afford 2,7-diphenyltropone

(39)36 in yields of 29-44 per cent. Tropone 39 crystallized
from absolute ethanol as pale-yellow plates, m.p. 131-132.50

(lit.90 m.p. 1330). The infrared spectrum (KBr) was

identical with that reported by Mukai.90

Reaction of l-diethylamino-1,3-butadiene (38) with
diphenylcyclobutadienoquinone (23).-A solution of 0.125 g.

(1.00 mmole) of freshly distilled 38 in 2 ml. benzene was

added in one portion to a solution of 0.200 g. (0.855 mmole)

of quinone 23 in one ml. of benzene. The mixture turned

very dark immediately. The benzene solution was refluxed

under argon for 12 hours. Work-up of the reaction mixture

as described in reference 36 resulted only in the isolation

of dark-red intractable tars.

Repetition of the above experiment by slowly adding

a solution of enamine 38 to a stirred solution of quinone

23 at -78, stirring for 5 hours, and then allowing the mix-

ture to warm to room temperature gave the same result as

found above.









Attempted reaction of l-diethylamino-l,3-butadiene

(38) with 1,2-diphenyltetrafluorocyclobutene (21).-A solution

of 0.125 g. (1.00 mmole) of freshly distilled 38 in 3 ml. of

benzene was added in one portion to a solution of 0.250 g.

(0.900 mmole) of cyclobutene 21 in 2 ml. of benzene. The

mixture was refluxed under argon for 64 hours. The benzene

solution was diluted with 30 ml. of ether and then washed

with two 10 ml. portions of 5 per cent hydrochloric acid

and one 10 ml. portion of saturated saline solution. After

drying over sodium sulfate the solvent was removed on a

rotatory evaporator to yield a yellow oil. Crystallization

from hexane gave 0.159 g. (two crops) of unchanged 21 (64%

recovery). The melting point and infrared spectrum of this

material were identical with those of a known sample.

l-Acetoxy-. 3-butadiene (40).-1-Acetoxy-1,3-butadiene

was prepared as described in the literature.91 The product
20
was a colorless liquid, b.p. 36-380 (12.5 mm.), nD 1.4688
91 20
(lit.91 b.p. 42-43/16 mm., n 0 1.46870). The diene was

stored under argon in the dark at 0 with a trace of

phenanthrenequinone added.

Attempted reaction of 1-acetoxy-1,3-butadiene (40)

with diphenylcyclobutadienoquinone (23).-To a solution of

0.132 g. (0.564 mmole) of quinone 23 in 3 ml. of benzene was
added in one portion a solution of 0.122 g. (1.09 mmoles)

of l-acetoxy-1,3-butadiene (40) in 2 ml. of benzene. The









resulting solution was refluxed under argon for 12 hours.

Removal of the solvent under a stream of argon gave a yellow

oil which crystallized upon addition of petroleum ether

(b.p. 30-800). The yellow solid thus obtained was identi-

fied as unchanged 23 by its melting point and infrared

spectrum. The recovery was 0.125 g. (93%).

Diphenylcyclobutadienocuinone monotosylhydrazone

(47).-The procedure of Blomquist and LaLancettela was used

with minor modifications. A mixture of diphenylcyclobuta-

dienoquinone (23) (0.500 g.; 2.14 mmoles) and tosylhydrazine

(0.420 g.; 2.26 mmoles) was dissolved in 15 ml. of absolute

ethanol containing 1 per cent by weight hydrogen chloride.

After stirring at room temperature for 18.5 hours the

precipitated yellow solid was collected by filtration and

washed with absolute ethanol and hexane. The yield of 47

was 0.712 g. (83%), m.p. 184-1870 (dec.) (lit.17a m.p. 188-

1890).

Elemental analysis of the monotosylhydrazone as ob-

tained above gave consistently low values for the carbon

content. In addition, a single analysis for nitrogen and

sulfur also gave values which were less than theoretical.

Shown below is the analytical data for a sample of 47

prepared by recrystallization from chloroform-hexane, m.p.

185.5-1870 (dec.).









Anal. Calcd. for C23H18N203S: C, 68.65; H, 4.51;
N, 6.96; S, 7.97. Found: C, 66.95; H, 4.31; N, 6.32; S,

7.66.

The infrared spectrum (KBr) showed absorption bands
at 3.15 (s), 3.29 (m), 5.67 (s), 5.99 (w), 6.26 (s), 6.35

(m), 6.46 (m), 6.69 (w), 6.77 (m), 6.95 (m), 7.13 (s),
7.38 (s), 7.47 (s), 7.73 (m), 8.22 (w), 8.39 (m), 8.59 (s),

9.17 (s), 9.34 (m), 9.57 (s), 9.75 (s), 10.01 (m), 10.16
(w), 10.70 (m), 10.87 (w), 11.56 (s), 12.18 (s), 12.35 (s),
12.75 (s), 13.08 (s), 13.45 (s), 14.15 (s), and 14.55 (s) ).
The ultraviolet spectrum acetonitrilee) showed max
max
at 225 my (C 23,600), 285 (26,900), 297 sh. (26,100), and

335 sh. (12,600). The spectrum showed no maxima in the
visible region. The yellow color of the compound can be

accounted for by the fact that the maximum at 285 my trails

to 440 my.

The n.m.r. spectrum (CDCl3) showed resonance signals
at T 1.15 (broad singlet, N-H), 1.78-2.80 (complex multi-
plet, aromatic protons), and 7.58 (sharp singlet, CH3),
with area ratios of 0.91:14:2.90, respectively.

Monotosylhydrazone 47 can also be prepared in acetic
acid at room temperature. However, the yield, purity, and
crystalline form of the product are superior when ethanol
is used as the solvent. Diethyl a,a'-diphenylsuccinate,
the product of the reaction between ethanol and the bisketene









form of quinone 2,17a was not formed in any detectable

amount during the preparation of tosylhydrazone 47 in

ethanol. Methanol also appears to be a suitable solvent for

the preparation of 4717a

Sulfuric acid hydrolysis of diphenylcyclobutadieno-

quinone monotosylhydrazone (47).-Tosylhydrazone 47 (200 mg.;

0.497 mmole) was dissolved in 96 per cent sulfuric acid (5

ml.) and the resulting dark-brown solution stirred at room

temperature for one hour. The solution was poured onto ice

and the aqueous mixture extracted with chloroform. The

chloroform layer was washed with 5 per cent sodium bicarbo-

nate solution and dried over sodium sulfate. Removal of

the solvent on a rotary evaporator yielded an orange oil

which crystallized from chloroform-hexane to give 69 mg.

of a yellow solid, m.p. 88-91. This material was tritu-

rated with boiling hexane containing a small amount of

chloroform and filtered while hot to remove a trace amount

of insoluble orange solid. The filtrate was evaporated to

dryness and the above procedure repeated. Removal of the

solvent gave a yellow oil which crystallized from chloro-

form-hexane to give 34 mg. of a yellow solid, m.p. 93-96.5.

The infrared spectrum of this material was identical with

that of a known sample of diphenylcyclobutadienoquinone (23).

The qualitative ultraviolet spectrum exhibited maxima and

relative peak intensities which were identical with those of









a known sample of the quinone. The yield of crude 23 was

59 per cent; the yield of purified 23 was 29 per cent.

Attempted preparation of the bistosylhydrazone

derivative of diDhenylcyclobutadienoquinone (23).

A. A mixture of 0.100 g. (0.248 mmole) of tosylhydra-

zone 47 and 0.050 g. (0.269 mmole) of tosylhydrazine was

dissolved in 5 ml. of chloroform. Five ml. of absolute

ethanol containing 1 per cent by weight hydrogen chloride

was added and the resulting solution stirred at room

temperature for 13 hours. The solution was concentrated

and cooled to give 0.066 g. (66% recovery) of unchanged 47,

which was identified by its melting point and infrared

spectrum.

B. A suspension of 0.200 g. (0.497 mmole) of tosyl-

hydrazone 47 and 0.100 g. (0.557 mmole) of tosylhydrazine

in 6 ml. of absolute ethanol containing 6 drops of glacial

acetic acid was heated at reflux for 48 hours. Undissolved

solid was present in the reaction mixture during the entire

reflux period. The mixture was cooled to room temperature

and filtered to give 0.058 g. of yellow crystals, m.p.

217-2190 (dec.). Two recrystallizations from chloroform-

hexane gave this compound as small yellow needles, m.p.

224.5-225.5 (dec.). The elemental analysis of this ma-

terial did not agree with that calculated for a bistosyl-

hydrazone derivative.









Anal. Calcd. for C30 H N40S2: C, 63.15; H, 4.59;
N, 9.82; Found: C, 69.21; H, 4.99; N, 9.83.

The infrared spectrum (KBr) showed absorption bands

at 5.23 (s), 5.91 (w), 6.09 (s), 6.27 (m), 6.36 (w), 6.47

(s), 6.77 (m), 6.94 (s), 7.30 (s), 7.38 (s), 8.45 (s),

8.56 (s), 8.80 (w), 9.33 (s), 10.02 (w), 11.48 (m), 11.68

(m), 12.30 (m), 12.68 (m), 13.32 (m), and 14.58 (s) y.

The qualitative ultraviolet spectrum acetonitrilee)

showed Xmax at 228 mu (relative E 1.38), 307 (1.92), and

392 (1.00).

The structure of this product remains unassigned.
17a
Blomquist and LaLancettea report the isolation of a com-

pound (m.p. 239-2400) which was presumed to be the bis-

tosylhydrazone derivative of quinone 25. This material was

obtained from the mother liquors of a preparation of the

monotosylhydrazone and gave a correct elemental analysis

for nitrogen.

Monotosylhydrazone 47 is stable under the reaction

conditions employed above. Refluxing 47 in absolute

ethanol containing a trace of glacial acetic acid for 71

hours resulted only in the recovery of unchanged monotosyl-

hydrazone.









Attempted preparation of diazodiphenylcyclobutenone

(48a).

A. To a solution of 0.201 g. (0.498 mmole) of tosyl-

hydrazone 47 in 5 ml. of methylene chloride was added 5.00

ml. of a 0.100 N sodium hydroxide solution (1.00 equiva-

lents). The methylene chloride layer turned an immediate

dark red. The mixture was stirred for 3 hours at room

temperature. At the end of this time the methylene chloride

layer was still dark red and the aqueous layer was pale

yellow. The methylene chloride layer was separated and

water added. Upon shaking the organic solution turned

yellow. The organic layer was separated, dried over sodium

sulfate, and the solvent removed on a rotary evaporator.

Recrystallization of the yellow residue from chloroform-

hexane gave 0.176 g. (88% recovery) of unchanged 47 which

was identified by its melting point and infrared spectrum.

B. Addition of excess triethylamine to a chloroform

solution of tosylhydrazone 47 gave a dark-red solution.

Addition of hexane caused precipitation of unchanged 47

(85% recovery).

C. A solution of 0.300 g. (0.747 mmole) of tosyl-

hydrazone 47 in 4 ml. of tetrahydrofuran was cooled to 0.

To this stirred solution was added 0.53 ml. of a 1.59 M

solution of n-butyllithium (0.843 mmole) in hexane under

an atmosphere of argon. The solution turned dark-red









immediately but no precipitate formed. The solvent was

removed on a rotary evaporator to yield an amorphous red

solid which was dried further at 0,2 mm. The reaction flask

was connected to a water-cooled condenser, evacuated to 0.2

mm., and immersed in a bath at 1000. The temperature of the

bath was raised to 1400 over a period of one hour and main-

tained at 1400 for an additional hour, During this time the

solid in the flask turned from red to black in color but no

material distilled or sublimed into the condenser. Examina-

tion of the residue in the flask revealed only the presence

of carbonaceous material.

D. A chloroform solution of tosylhydrazone 47

(0.168 g.; 0.418 mmole) was added to an 11 x 1.1 cm. column

of basic alumina (Merck 71707) packed in chloroform. The

alumina column turned bright orange upon contact with the

tosylhydrazone solution. The orange color traveled the

length of the column but the eluates were yellow. The

column was eluted with chloroform (400 ml.) until the

eluates were colorless. Removal of the solvent on a rotary

evaporator gave a yellow residue which was crystallized

from chloroform-hexane (three crops) to give 0.100 g. (60%

recovery) of unchanged 47. Removal of the solvent from the

final filtrate left no residue.

E. A mixture of 0.200 g. (0.497 mmole) of tosyl-

hydrazone 47 and 5.00 ml. of an 0.100 N sodium hydroxide










solution (1.01 equivalents) was stirred in a stoppered flask

at room temperature. The tosylhydrazone was insoluble in

the basic solution but formed a fine suspension with stir-

ring. This suspension was orange after 10 minutes and

orange with a metallic luster after one hour. Yellow solid

settled beneath a bright-red aqueous solution when stirring

was stopped. After 6 days the suspension was yellow and,

when stirring was stopped, yellow solid settled beneath a

colorless aqueous solution. After 7 days at room tempera-

ture the mixture was extracted with chloroform. The chloro-

form layer was separated, washed twice with water and dried

over magnesium sulfate. Removal of the solvent on a rotary

evaporator gave a yellow solid which was recrystallized

from chloroform-hexane to yield 0.100 g. (three crops, 50%

recovery) of unchanged 47 which was identified by its

melting point and infrared spectrum. Removal of the sol-

vent from the final residue gave a brown, intractable

residue. The infrared spectrum (CHC13) of this residue

showed a strong band at 4.74 microns but all attempts to

isolate a solid product were unsuccessful. Acidification

of the combined aqueous layers followed by extraction with

chloroform gave a yellow heat-sensitive solid which decom-

posed upon attempted recrystallization.









1-Cyano-1-DhecnyrcycloDrooane (65).-The procedure

followed was that of Tilford, Van Campen and Shelton.5 A

2-1. three-necked flask fitted with a dry-ice condenser,

gas-inlet tube, dropping funnel, and magnetic stirrer was

cooled to -360 in a dry ice-ethylene dichloride bath.

Approximately 500 ml. of liquid ammonia was slowly condensed

in the flask. After the addition of 0.5 g. of ferric

nitrate, 40.7 g. (1.77 g.-atoms) of sodium metal (Baker

reagent) was added with stirring over a period of 30 minutes.

Four hours after the addition of sodium was complete the

initial blue color of the solution had faded to gray and

freshly distilled phenylacetonitrile (100 g.; 0.85 mole)

was added over a 20 minute period. The cooling bath was

changed to a dry ice-chloroform bath (-640) and 156 g.

(0.85 mole) of ethylene dibromide in 500 ml. of dry ether

was added over a period of 1.5 hours. At the end of addi-

tion the cooling bath was removed and the ammonia allowed

to evaporate over a period of 6 hours while the original

volume was maintained by the addition of dry ether. The

resulting ether solution was refluxed for two hours. The

mixture was cooled to room temperature and 400 ml. of water

and 500 ml. of benzene were added. The organic layer was

separated, dried over sodium sulfate and the ether and

benzene removed by slow distillation. Distillation of the

residue on a spinning-band column gave a forerun of 23 g.









of unchanged phenylacetonitrile, b.p. 109-1200 (17 mm.),

n20 1.5250 (lit.92 n5 1.5211), followed by 50.5 g. (42%)

of l-cyano-l-phenylcyclopropane as a colorless oil, b.p.

125-11 (17 mm.), n20 1.5581 (lit.95 b.p. 125/15 mm., n20

1.5382). The infrared spectrum of this material was

identical with that reported in reference 93.

1-Phenylcyclopropyl phenyl ketone (66).57 A solution

of phenylmagnesium bromide was prepared under an argon

atmosphere from 2,92 g. (0.120 g.-atom) of magnesium and

19.60 g. (0.125 mole) of bromobenzene in 125 ml. of dry

ether. To this solution was added 15.00 g. (0.105 mole) of

l-cyano-l-phenylcyclopropane (65) dissolved in 75 ml. of

ether over a period of 45 minutes. The ether solution re-

fluxed gently during the addition. The stirred reaction

mixture was then refluxed for 72 hours. The mixture was

cooled to 0 and 150 ml. of 10 per cent hydrochloric acid

was added, causing the formation of copious amounts of solid

material. Benzene (100 ml.) was added and the ether removed

by distillation. An additional 100 ml. of benzene was added

and the two-phase mixture refluxed with stirring for 14

hours. At the end of this time all solid material had dis-

solved and the benzene solution was dark green. The benzene

layer was separated and the aqueous layer extracted twice

with ether. The combined organic solutions were washed with

5 per cent sodium bicarbonate solution, causing the color to









change from green to red-brown. The organic layer was

washed with saturated saline solution and dried over

magnesium sulfate. Removal of the solvents on a rotary

evaporator yielded a black oil. Short-path distillation

gave 18.0 g. of a yellow oil, b.p. 130-1350 (0.45 mm.).

Crystallization from 95 per cent ethanol gave 10.25 g. (44%)

of 1-phenylcyclopropyl phenyl ketone as slightly yellow

crystals, m.p. 66-71. Further recrystallization from 95

per cent ethanol gives colorless crystals, m.p. 73-740

(lit.57a m.p. 75.6-73.90). The infrared spectrum of this

material was identical with that reported in reference 57b.

1-Phenylcyclopropyl phenyl carbinol (67).-To a

stirred mixture of 1.71 g. (0.0450 mole) of lithium aluminum

hydride in 150 ml. of absolute ether at 00 was added 4.70 g.

(0.0212 mole) of 1-phenylcyclopropyl phenyl ketone (66) in

75 ml. of absolute ether over a period of 30 minutes. The
reaction mixture was stirred at 00 for 30 minutes, at room

temperature for one hour, and at reflux for 45 minutes. The

solution was cooled to 0 and decomposed by addition of

ethyl acetate followed by 10 per cent hydrochloric acid.

The ether layer was separated and the aqueous layer extracted

with ether. The combined ether solutions were washed twice

with water and dried over sodium sulfate. Removal of the

solvent on a rotary evaporator gave a colorless oil. Distil-

lation yielded 3.84 g. (81%) of 1-phenylcyclopropyl phenyl









carbinol as a colorless, very viscous oil, b.p. 130-1330
21
(0.50-0.65 mm.), n2 1.5822.
Anal. Calcd. for C16H160: C, 85.68; H, 7.19. Found:

C, 85.60, H, 7.07.

The infrared spectrum (neat) showed absorption bands

at 2.89 (s), 3.27 (m), 3.46 (w), 6.26 (w), 6.70 (m), 6.90

(m), 9.66 (m), 9.78 (m), 12.66 (w), 13.12 (m), 14.05 (s),
and 14.35 (s) ).

The n.m.r. spectrum exhibited resonance signals at T

2.97 (singlet,aromatic protons), 5.67 (singlet, OH), 6.75
(singlet, CH), and 9.22 (unresolved doublet, cyclopropyl

protons), with area ratios of 10:1:1:4, respectively.

1-Phenylcyclopropyl phenyl ketone tosylhydrazone

(68).-A mixture of 1-phenylcyclopropyl phenyl ketone (66)

(2.595 g.; 11.7 mmoles) and tosylhydrazine (3.270 g.; 17.6

mmoles) was heated to reflux in 25 ml. of absolute ethanol

containing 6 drops of glacial acetic acid. Colorless

crystals separated from the hot solution after two days at

reflux. After refluxing for seven days the solution was

cooled and filtered to yield 5.316 g. of colorless crystals.

This material was triturated with 20 ml. of boiling ethanol,

cooled, and filtered to give 3.240 g. (71%) of tosylhydra-

zone 68 as colorless crystals, m.p. 191-1935 (dec.). The

analytical sample was prepared by one recrystallization from

absolute ethanol and had m.p. 191-1935 (dec.). The melting









point of this material varies with crystalline form. The

small crystals obtained by recrystallization have m.p. 191-

1935 but the large, very hard crystals which separate from

hot ethanol during the preparation have melting point as

high as 1980. The yield of 68 by the procedure described

above was consistently 66-71 per cent.

Anal. Calcd. for C25H22 202S: C, 70.75; H, 5.68.

Found: C, 70.91; H, 5.80.

The infrared spectrum (KBr) showed absorption bands

at 3.06 (m), 3.26 (w), 6.27 (m), 6.70 (m), 6.93 (m), 7.30

(s), 7.43 (m), 7.55 (m), 8.53 (s), 9.35 (m), 9.48 (m),

9.72 (m), 10.15 (m), 11.28 (m), 12.40 (m), 12.94 (s), 15.23
(s), 14.14 (s), and 14.40 (s) p.
The n.m.r. spectrum (CDCl3) exhibited the following

resonance signals: a broad singlet at T 1.92 (N-H, rela-

tive area 1.07), two multiplets centered at 2.23 and 2.95

(aromatic protons, combined relative area 14.0), a sharp

singlet at 7.57 (CH relative area 3.14), and a pair of

unresolved multiplets centered at 8.53 and 8.75 (cyclopropyl

protons, relative area 3.82).

Attempts to improve the yield of tosylhydrazone or

to shorten the reaction time required were unsuccessful.

These experiments are briefly described below.

A. Refluxing equimolar amounts of ketone and tosyl-

hydrazine in ethanol containing a trace of acetic acid for










B. Repeating the experimental conditions in A but

refluxing for 72 hours gave a 19 per cent yield of tosyl-

hydrazone.

C. Repeating the experimental conditions in A but

refluxing for 166 hours gave a 39 per cent yield of tosyl-

hydrazone.

D. Refluxing the ketone with a 1.07 mole excess of

tosylhydrazine in glacial acetic acid for 61 hours gave a

black solution which yielded no product but from which 82

per cent of the starting ketone was recovered.

E. Refluxing the ketone with a 1.55 mole excess of

tosylhydrazine in n-butanol containing a trace of acetic

acid for 70 hours yielded a deep-violet solution and a 7

per cent yield of relatively impure tosylhydrazone,

1,2-Diphenylcyclobutene (24).55 To a solution of

tosylhydrazone 68 (2.745 gl; 7.05 mmoles) in 50 ml. of dry

N-methyl-2-pyrrolidone was added 0.a55 g. (8.07 mmoles) of

freshly prepared sodium methoxide. The solution was stirred

for 3 minutes and then immersed in a bath at 1200. Nitrogen

evolution began immediately and was essentially complete

after 12 minutes. The solution was dark orange after 2

minutes of heating, red after 4 minutes, and light orange

after 7 minutes. After 12 minutes at 1200 the solution was

cooled and poured into 75 ml. of water. The resulting oil

was extracted into hexane. The hexane solution was washed









5 times with water and dried over sodium sulfate. Removal
of the solvent on a rotary evaporator yielded a yellow oil
which was dissolved in hexane and filtered through a column
of alumina (Merck 71707) using hexane as the eluant. The

resulting colorless oil was crystallized from methanol at

-780 to give 1.105 g. (76%) of 1,2-diphenylcyclobutene as

colorless plates, m.p. 51-55.5. The analytical sample was

obtained by two further recrystallizations from methanol and

had m.p. 53-54. The yield of 24 by this method of prepa-
ration was consistently 66-76 per cent.
Anal. Calcd. for C16H14: C, 95.16; H, 6.84. Found:

C, 95.04; H, 6.97.
The infrared spectrum (KBr) showed absorption bands

at 5.21 (m), 5.35 (m), 6.25 (m), 6.68 (m), 6.91 (m), 7.50

(m), 8.26 (m), 9.52 (m), 9.61 (w), 9.79 (w), 10.80 (m),

10.95 (m), 12.46 (w), 12.99 (m), 15.35 (s), 14.15 (w), and
14.55 (s) ..
The ultraviolet spectrum (isooctane) showed %max at

224 my sh. (E 25,200), 227.5 (24,100), 256 sh. (13,500), 297
(18,400), 507 sh. (17,500), and 522 inf. (10,800).
The n.m.r. spectrum (CDC1 ) showed a complex multi-

plet centered at T 2.58 (aromatic protons) and a sharp
singlet at 7.24 (methylene protons), with an area ratio of

2.4:1.0, respectively.







91

Therm al isomerization of 1,2-diphenylcyclobutene (24)

in the presence of o-benzoquinone.-A mixture of 0.055 g.

(0.267 mmole) of 1,2-diphenylcyclobutene and 0.027 g.

(0.250 mmole) of D-benzoquinone dissolved in 3 ml. of xylene

was refluxed for 26 hours. The xylene was removed under a

stream of argon and the residue triturated with boiling

hexane. Filtration of the hot solution gave a white solid

which was dissolved in boiling methanol and filtered while

hot to remove a trace of insoluble material. Cooling

afforded 0,020 g. (25%) of 6,7-diphenyl-4a,5,8,8a-tetra-

hydro-l,4-naphthoquinone (71) as pale-yellow crystals, m.p.
72
160-1620 (lit.2 m.p. 1650). Recrystallization from methanol

gives pale-yellow needles, m.p, 161-1635. The infrared

spectrum (KBr) showed absorption due to carbonyl stretching

vibration at 5.95 p.

Thermal isomerization of 1.2-diphenylcyclobutene

(24) in the presence of 1,4-naphthoquinone.-A mixture of

0.107 g, (0.519 mmole) of 1,2-diphenylcyclobutene and 0.080

g. (0.507 mmole) of freshly sublimed 1,4-naphthoquinone dis-
solved in 3 ml, of xylene was refluxed for 26 hours. The

xylene was removed under a stream of argon and the residue

recrystallized from acetone and then from methanol to give

0.395 5. (522) of 2,$-diphenyl-1,,,a,9a-tetrahydro-9l,0-

anthraquinone (72) as a white. amorphous solid, m.p. 165-

166.50 (lit.72 m.p. 175-1760). The infrared spectrum (KBr)

showed absorption due to carbonyl stretch at 5.92 i.










To a solution prepared by dissolving one potassium

hydroxide pellet in 5 ml. of absolute ethanol was added 24

mg. (0.066 mmole) of quinone 72. The resulting solution was

dark red. When air was bubbled through the solution for 15

minutes the red color disappeared and yellow needles pre-

cipitated. Filtration gave 17 mg. (70%) of 2,3-diphenyl-

9,10-anthraquinone (73), m.p. 211.5-212.50 (lit.72 m.p.

211-212). The infrared spectrum (KBr) showed absorption

due to carbonyl stretch at 5.98 p.

Thermal isomerization of 1.2-dinhenylcyclobutene (24):

bromination of the product.-1,2-Diphenylcyclobutene (0.042

g.; 0.204 mmole) was heated in an open tube at 1900 for 7

minutes. The resulting yellow oil, which was not entirely

fluid, was dissolved in chloroform and a solution of bromine

in carbon tetrachloride added until the bromine color per-

sisted. Upon warming under a stream of argon to remove the

solvent the solution turned a deep blue. The solvent was

removed and the residue dissolved in boiling acetone and

filtered to remove insoluble blue solid. The process of

war-ing the filtrate and filtering was repeated until blue

precipitate was no longer formed. The resulting acetone

solution was evaporated to dryness and the residue dissolved

in boiling ethanol. The hot solution was filtered to remove

a trace of insoluble material and cooled to give 0.030 g.










(40%) of 1,4-dibromo-2,5-diphenyl-2-butene (74) as glisten-

ing needles, m.p. 148-150.50 (lit.72 m.p. 145-1470)

Heating a neat sample of 24 at 1550 for 3.5 hours

afforded a yellow gum. This material was dissolved in

chloroform and treated with a bromine-carbon tetrachloride

solution until the bromine color persisted. Upon warming

the solution became very dark with evolution of hydrogen

bromide. Removal of the solvent under a stream of argon

gave a blue residue which formed a hard, amorphous, metal-

lic-blue mass when acetone was added. None of the desired

dibromide could be isolated.

Thermal isomerization of 1,2-diphenylcyclobutene (24):

n.m.r, spectrum of the product,-A neat sample of 1,2-diphenyl-

cyclobutene was heated in an open tube at 1900 for 3 minutes

(ca, 1.3 half-lives). The resulting fluid oil was dissolved

in CDC13 and the n.m.r. spectrum determined immediately.

The spectrum showed a complex multiple centered at T 2.74

(aromatic protons), an AB quartet (J = 1.8 cps) centered at

4.67 (butadiene methylene protons), and a sharp singlet at

7.24 (cyclobutene methylene protons). A comparison of the

relative areas of the cyclobutene and butadiene methylene

protons indicated that 54 per cent of the cyclobutene had

undergone isomerization. When the extent of isomerization

was calculated by comparing the relative area of the aromatic

protons with that of the cyclobutene methylene protons the









value of 58 per cent was obtained. The similarity of the

above two values indicates that little, if any, polymeriza-

tion has taken place. Polymer was not detectable in the

spectrum described above.

When a neat sample of 24 was heated under argon at

1550 for 3.5 hours a yellow gum resulted. The n.m.r.

spectrum (CDC13) of this material showed, in addition to

aromatic protons, small peaks at T 6.54, 7.24, and 8.73. A

large, relatively broad peak was centered at T 8.00. There

was no detectable absorption in the vinyl region of the

spectrum.

Kinetic runs.-The rate of valence isomerization of

1,2-diphenylcyclobutene was determined by following the

decrease in optical density of the long-wavelength ultra-

violet band of this compound as a function of time. This

absorption band appeared at 297 mq in isooctane, n-propanol,

and n-propionitrile and at 299.5 mu in decalin. Extrapola-

tion of the ultraviolet spectrum of the product of the

isomerization, 2,5-diphenyl-l,3-butadiene (70), as reported

by Cope, showed that absorption at 297 my was insignifi-

cant with a < 200. The spectra of the infinity points of

the kinetic runs (9.5-15.7 half-lives) characteristically

showed optical densities at 297 my which were 1-2 per cent

of the optical densities at zero time. A plot of optical

density against concentration for isooctane solutions of




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