Structure and reactivity in the heterotropilidene series and other studies

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Structure and reactivity in the heterotropilidene series and other studies
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Full Text










Structure and Reactivity in the Heterotropilidene
Series and Other Studies











By

ROBERT MERRIFIELD WHITE


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
1972













DEDICATION


This dissertation is dedicated to all of the people, places,

animals, and things which have made the past four years a

worthwhile experience in Life.














ACKNOWLEDGEMENTS

The author wishes to thank his research director, Prof.

Merle A. Battiste, for excellent guidance on this project,

helpful discussions, and, most of all, moral support when

it was needed. The author would also like to thank the Palenik

Group, especially M. Mathew, for the generous use of their

x-ray facilities and cheerful help on structure 67; Dr. R.W.

King for the computer solutions of the NMR spectra of com-

pounds 79 and 80; and Dr. R. -Rehburg for samples of com-

pounds 2, 3, 10, and 11 and the excellent groundwork done

on the project before the author took over.

The author also wishes to recognize and thank The

Ghetto, Alpha Chi Sigma and its members, especially S.R.,

S.W., P.F.E., J.Hi., M.K., H.J., and R.K.; 1743, SCL, L&N,

T.E.H., The Zoo, The Rat, R.W.C.V., C.C.V., R.L., Huntsville,

Nashville, and all of the other people, places, animals, and

things whose sheer volume space does.not permit mention of

but which have made the past four years more than just a

pure academic experience.

The author also wishes to thank his wife, Ann, for

providing moral support when it was needed and his son,

Robbie, for being so patient these past four years.


iii





















"I remember when this whole thing began
No talk of God then we called you a man."

Jesus Christ Superstar, 1970













PREFACE

As part of a general study of the Diels-Alder reaction
of tetrazines with alkenes, it was discovered independently
in 1966 by Sauer and Heinrichs,1 and Battiste and Barton2
that sym-triphenylcyclopropene reacts with 3,6-diphenyl-
1,2,4,5-tetrazine (1) at 20 to 780 to produce a yellow com-
pound (2) C35H26N2 which, on heating (1000 or greater),
isomerizes to an almost colorless compound (3) which, on
further heating (2300), decomposes into benzonitrile and sym-
tetraphenylpyrrole. The results of both investigations are
summarized in Scheme 1.


H
H 0 N
N N Y H NV
I II + 0 -~ 2 c --3"/

T 0 0
0 +

1 0CN

Scheme 1
Sauer was of the opinion that 2 is in the diazanor-
caradiene form, 1,2,5,6,7-pentaphenyl-3,4-diazabicyclo[4.1.0]-
hepta-2,4-diene (4). Battiste, however, argued that 2 should
be described as 3,4,5,6,7-pcntaphcnyl-5H-1,2-diazepine (5).















-N-N N=N

4 5


Both Sauer and Battiste agreed that 2,5-diphenyl-3,4-

diazabicyclo[4.1.0]hepta-2,4-diene (6) 1'23 and 2,5,7-

triphenyl-3,4-diazabicyclo[4.1.0]hepta-2,4-diene (7)4 and

other diazanorcaradienes with no phenyls at C-I and C-6

exist exclusively in the diazanorcaradiene form at room

temperature.

Sauer based his argument for 4 on the fact that the UV

spectrum of 2 is quite similar to that of 6 even though

Maier3 had previously shown that substituents in the 1- and

6-positions imposed steric restrictions on the phenyls in

the 2- and 5-positions causing a hypsochromic shift in the

ultraviolet. Thus, there was some doubt as to whether the

UV of 4 and the UV of 6 could be compared.

Battiste suggested that the low-field position of the

only non-aromatic absorption in the NMR spectrum of 2

indicated an allylic type signal rather than a cyclopropyl

type signal. Battiste also felt that the phenyls in the 1-

and 6-positions would facilitate the disrotatory opening of

the initially formed 4 to give a diazacycloheptatriene

system.









Sauer proposed that product 3 is the result of dis-

rotatory ring opening of 4 to give the SH-diazepine 5 or one

of its hydrogen-shifted (except to nitrogen) products. Again

Sauer based his arguments on the UV spectrum of 3,citing

extended conjugation as being responsible for the spectrum.

On the basis of its facile conversion to tetraphenyl-

pyrrole and benzonitrile, Battiste tentatively proposed the

bicyclic structure 8 for isomer 3.


H



N-N /


0

8

The reaction of dimethyl 1,2,4,5-tetrazine-3,6-dicar-

boxylate (9) with sym-triphenylcyclopropene gives products

10 and 11 which are analogous to 2 and 3 above. Since the

product 11 shows nonequivalent ester methyls in the NMR,

Sauer5 assigned to it the structure 12.








H3 C2C N=N xC02CH3


vii









It was shown by Rehburg and Battiste6 that mixtures of

pyrroles are obtained from diaza species similar to 3 or 11

when the tetrazine has substituted phenyls, methyls,or

carbomethoxy groups attached to it as illustrated below in

Scheme 2.

H

N-N R2OO R N R
RJ R -- 2 -- >3' 200 R + OCN+
N=N 0
+ H


0+ RCN

H 0 0 0

R = CH3, p-H3C-C6H4, C02CH3
Scheme 2

At the time this work was initiated, it still was not

known definitely whether 2 existed as diazanorcaradiene or

SH-diazepine, nor had the structure of 3 been established.

Also, no mechanistic details on the conversion of 2 to 3

were available. Chapter I deals in some detail with the

structures of 2 and 3 and the mechanism of the thermal

isomerization of 2 to 3.

When this investigation was begun, the aromaticity and

stability of the cycloheptatrienylium or tropylium cation

(13) were well known.7' Also, the aromaticity of cyclo-

heptatrienone or tropone (14) was well-documented.7'8


viii












0 O0






13 14

By contrast, the analogous 1,2-diazacycloheptatrieny-

lium cation (15) was a complete unknown at the beginning of

this work. Only one 1,2-diazatropone derivative, 16, had

been reported.9 In acid, 16 did not protonate on oxygen to

form the aromatic dibenzohydroxydiazatropylium cation, but,

rather, it protonated on nitrogen to form an amine salt as

illustrated in Scheme 3.


0 O-H






15 16
0




N=N
H
Scheme 3

Since at the beginning of this investigation it was

thought that compounds such as 2 existed in the open 5H-

diazepine form, the possibility of synthesizing the diaza








analogs of the tropylium cation and tropone appeared to be

a feasible project. The diazatropylium cation-diazatropone

problem will be dealt with in Chapter IV.

Also, the tetrazines which are used in the synthesis of

many of the diazanorcaradienes and diazepines present them-

selves as an interesting heteroaromatic series. The spec-

tral properties of some of the more interesting members of

this series will be examined in some detail along with

members of related aromatic systems in Chapter III.














TABLE OF CONTENTS


ACKNOWLEDGEMENTS ......... ............ ..

PREFACE ................................................

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

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

ABSTRACT ........................... .. ...... ..

Chapter

I. THE DIAZANORCARADIENE-DIAZEPINE REARRANGEMENT.

Results and Discussion ..................

II. MASS SPECTRAL CORRELATIONS ...................

Introduction ............................

Results and Discussion ...................

III. CYCLOPROPYL CONJUGATION IN HETEROAROMATIC
SYSTEMS ......................................

Cyclopropyl Conjugation ................

Synthesis ............... ........

Dicyclopropyltetrazine and Dicyclopropyl-
pyridazine The Ground State ...........

Dicyclopropyltetrazine and Dicyclopropyl-
pyridazine The Excited State ..........

IV.. THE DIAZATROPYLIUM CATION AND DIAZATROPONE ...

Attempted Syntheses of 1,2-Diazatropylium
Cations .............. .. .................

Attempted Syntheses of 1,2-Diazatropone

V. EXPERIMENTAL .................................

REFERENCES .............................................

BIOGRAPHICAL SKETCH ..........................

xi


Page

111

v

xii

Xiii

xv



1

1

44

44

46


80

80

83


90


112

130


130

150

159

211

215












LIST OF TABLES


Table Page

I Kinetic Parameters for the Thermal Isomeriz-
ation of 2 to 3 .................................. 3

II Bond Distances and Their Estimated Standard
Deviations in Diazepine 67 ...................... 37

III Bond Angles and Their Estimated Standard
Deviations in Diazepine 67 ...................... 38

IV Relative Intensities for Important Mass Spectral
Fragmentations of Diazanorcaradienes ...;........ 48

V Thermal Decomposition Data for Some 4H-
Diazepines ...................................... 51

VI Chemical Shift Data for Tetrazine 79 and
Pyridazine 80 ................................... 88

VII Magnetic Coupling Data for 79, 80, 85 and 86 .... 89

VIII Chemical Shift Data for iso-Propyl and Cyclo-
propyl Aromatic Compounds ....................... 111

IX Principal Absorbances for Some Tetrazines ....... 114

X Principal Absorbances for Some Pyridazines ...... 115

XI Proton Assignments for 96 ....................... 134


xii











LIST OF FIGURES


Figure Page

1 NMR spectrum of unknown 49 in CDC13 ............. 25

2 NMR. spectrum of unknown 49 in ds-pyridine ....... 28

3 ORTEP generated diagram of 3,7-bis(4-bromo-
phenyl)-4-(4-methylphenyl)-5,6-diphenyl-4H-
1,2-diazepine (67) .............................. 41

4 Mass spectrum of 1,2,5,6,7-pentaphenyl-3,4-
diazabicyclo[4.1.0]hepta-2,4-diene (2) .......... 56

5 Mass spectrum of 2,5-bis(4-bromophenyl)-7-
(4-methylphenyl)-1,6-diphenyl-3,4-diazabicyclo-
[4.1.0]hepta-2,4-diene (66) ..................... 60

6 Mass spectrum of 3,4,5,6,7-pentaphenyl-4H-1,2-
diazepine (3) .................................... 65

7 Mass spectrum of 3,7-bis(4-bromophenyl)-4-
(4-methylphenyl)-5,6-diphenyl-4H-1,2-
diazepine (67) .................................. 69

8 Mass spectrum of dimethyl 1,6,7-triphenyl-3,4-
diazabicyclo[4.1.0]hepta-2,4-diene-2,5-
dicarboxylate (10) .................................. 74

9 Mass spectrum of 7-(4-methylphenyl)-1,2,5,6-
tetraphenyl-3-,4-diazabicyclo [4. 0]hepta-2 ,4-
diene (68) ...................................... 77

10 NMR spectrum of 3,6-dicyclopropyl-l,2,4,5-
tetrazine (79) in CDC13 at NMR probe temperature
(400) ............................................ 94

11 NMR spectrum of 3,6-dicyclopropyl-l,2,4,5-
tetrazine (79) in CDC13 at -10 .................. 96

12 NNR spectrum of 3,6-dicyclopropyl-l,2,4,5-
tetrazine (79) in CDC13 at -30 ................. 98

13 NMR spectrum of 3,6-dicyclop'ropyl-l,2,4,5-
tetrazine (79) in CDC13 at -60 ................. 100

14 NMR spectrum of 3,6-dicyclopropyl-l,2,4,5-
tetrazine (79) in diphenyl ether at NMIR probe
temperature (40) ............................... 102


xiii








Figure Page

15 NMR spectrum of 3,6-dicyclopropylpyridazine
(80) in CDC13 at 42.50 .... ..................... 104

16 NMR spectrum of 3,6-dicyclopropylpyridazine
(80) in CDCI3 at -5.5 .......................... 106

17 NMR spectrum of 3,6-dicyclopropylpyridazine
(80) in CDC13 at -59.0 ............................ 108

18 Visible spectrum of 3,6-dicyclopropyl-
1,2,4,5-tetrazine (79) in ethanol ............... 119

19 Visible spectrum of 3,6-dicyclopropyl-
1,2,4,5-tetrazine (79) in cyclohexane ............ 121

20 UV spectrum of 3,6-dicyclopropyl-l,2,4,5-
tetrazine (79) in ethanol ....................... 123

21 UV spectrum of 3,6-dicyclopropyl-l,2,4,5-
tetrazine (79) in cyclohexane ................... 125

22 UV spectrum of 3,6-dicyclopropylpyridazine
(80) in ethanol ................................. 127

23 UV spectrum of 3,6-dicyclopropylpyridazine
(80) in cyclohexane ............................. 129

24 NMR spectrum of 3,5,7-triphenyl-4H-1,2-diazepine
hydrofluoroborate (99) in TFA/CDC13 at 17.00 .... 141

25 NMR spectrum of 3,5,7-triphenyl-4H-1,2-diazepine
hydrofluoroborate (99) in TFA/CDC13 at 1.5 ..... 143

26 NMR spectrum of 3,5,7-triphenyl-4H-1,2-diazepine
hydrofluoroborate (99) in TFA/CDC13 at -18.5 ... 145

27 UV spectrum of unknown 102 ...................... 149

28 UV spectrum of 4,5-diphenyl-3,6-dicarbomethoxy-
1-(1,2-diphenylcyclopropen-3-yl)-1,4-dihydro-
pyridazine-4-aldehyde (104) ...................... 154


xiv














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

STRUCTURE AND REACTIVITY IN THE HETEROTROPILIDENE
SERIES AND OTHER STUDIES

By

Robert Merrifield White

March, 1972

Chairman: M.A. Battiste
Major Department: Chemistry

It has been found that the reaction between sym-tri-

phenylcyclopropene and 3,6-diphenyl-l,2,4,5-tetrazine pro-

duces 1,2,5,6,7-pentaphenyl-3,4-diazabicyclo[4.1.0]hepta-

2,4-diene or pentaphenyldiazanorcaradiene which, on heating,

isomerizes to 3,4,5,6,7-pentaphenyl-4H-1,2-diazepine as

determined by x-ray studies. It has been demonstrated

conclusively that pentaphenyldiazanorcaradiene rearranges to

the 4H-diazepine via a carbon-shift rather than a hydrogen-

shift mechanism. The exact mechanism of the carbon shift

was not determined. Preliminary work on the decomposition

of 4H-diazepines into pyrroles and benzonitriles has also

been done.

2,5-Diphenyl-l,3,4-thiadiazole has been isolated in low

yield in the synthesis of 3,6-diphenyl-l,4-dihydro-l,2,4,5-

tetrazine from sulfur, ethanol, hydrazine hydrate, and

benzonitrile.









In the heteroaromatic series, it has been demonstrated

that cyclopropyl conjugation is present in the highly

interesting 3,6-dicyclopropyl-l,2,4,5-tetrazine and, as

anticipated, to a lesser extent, in 3,6-dicyclopropyl-

pyridazine in both the ground and excited states.

Attempts at synthesizing the diaza analogs of tropone

and the tropylium cation by standard methods met with no

success. However, some interesting rearrangements and new

compounds were observed.


xvi















CHAPTER I

THE DIAZANORCARADIENE-DIAZEPINE REARRANGEMENT


Results and Discussion

The first step taken in dissecting and analyzing the

thermal conversion of 2 to 3 outlined in Scheme 1 was to

determine the structure of compound 3. The structure of

3 was attacked using x-ray spectroscopy. It was decided

to employ the heavy atom technique by reacting sym-tri-

phenylcyclopropene with the then unknown 3,6-bis(4-iodo-

phenyl)-1,2,4,5-tetrazine (17) at elevated temperatures

to give directly 3 with two phenyl rings carrying iodine

atoms.

Since classical methods of synthesizing 17 had failed

previously,6 the recently developed method of Abdel-Rahman

et al.10 was used to produce the yellow dihydroderivative

of 17 which was then oxidized to the deep purple 17.

Unfortunately, 17 was contaminated with what is tentatively

identified as 2,5-bis(4-iodophenyl).-l,3,4-thiadiazole (18)

(see Chapter III) which was very difficult to remove due

to the gross insolubility of both 17 and 18. The thia-

diazole 18 could be separated from 17 only by chromato-

graphy over basic alumina with boiling xylene which tended

to completely decompose the tetrazine 17 unless it was

rapidly eluted from the column.









Reaction of 17, either chromatographed or crude, with

sym-triphenylcyclopropene in refluxing xylene gave the

desired substituted 3 without isolation of the intermediate

substituted 2. The x-ray analysis11 of the iodine-

substituted 3 showed that it has the 4H-diazepine structure

19.


E-I -C6H4


Obviously, the above described conversion of 10 to 11

should proceed in a manner analogous to the 2 to 3 conver-

sion and product 11 should have the 4H-diazepine structure

20 rather than structure 12 as assigned by Sauer.






H

H 3CO 2 C / 0C2CH3
N-N

20


At least formally, the conversion of 2 to 3 may be con-

sidered as two concerted suprafacial 1,5-hydrogen shifts12

from the open form of 2 as shown below in Scheme 4.










H 5 0


2 qP/ 3
4, \

N=N N-N

H

Scheme 4

The kinetics of the thermal isomerization of 2 to 3

were followed by NMR at 150 and 1400. Good first-order

kinetics were observed and the resulting kinetic para-

meters are given in Table I. The energy of activation (Ea)

was found to be 33.4 kcal/mole. The kinetics indicated that

the reaction is unimolecular and supported the mechanism

of Scheme 4.


Table I

Kinetic Parameters for the Thermal Isomerization of 2 to 3

temp. (C) k (sec-') AH* (kcal/mole) AS* (cal/mole-deg)

150.0 2.93 x 10-5 32.6 -3.14
140.0 1.07 x 10-5 32.6 -3.24


Taking the premise that two concerted 1,5-hydrogen

shifts were responsible for the conversion of 2 to 3, it

appeared of considerable mechanistic interest to examine

some systems in which the cyclopropane ring of the diaza-

norcaradiene does not carry three phenyl rings as in 2.

Two such systems are 21 and 22, which are simply 2 and 10

without a phenyl on the methylene carbon (C-7).













H- 3nCO H3C02C C02C 3
N-N N-N

21 22


Both 21 and 22 are readily synthesized by the cyclo-

addition of 1,2-diphenylcyclopropene'3 with 1 and 9 respec-

tively. The resulting adducts are bright yellow crystalline

compounds whose spectral and analytical properties define

their structure as that of the norcaradiene valence

tautomer.

The aromatic region of the NMR spectrum of 21 shows two

multiplets centered at T2.18 and 2.80 integrating in the

ratio 4:6 and a spike at 3.16 which accounts for ten pro-

tons. The lower field aromatic multiple is assigned to

the ortho protons of the phenyl rings attached to the

azine linkage. Deshielding of these ortho protons by the

electron-withdrawing and diamagnetically deshielding azine

linkage is assumed. The higher field multiple is assigned

to the further removed meta and para protons of the phenyls

at C-2 and C-4. The ten-proton spike which is at higher

field than either multiple accounts for the phenyls

attached to the cyclopropane ring. The two methylene (C-7)

protons, which are especially important for structural

identification, appear as two widely separated








sharp doublets at T6.31 (J = 5.5 Hz) and 8.68 (J = 5.5 Hz).

That the methylene protons appear as two doublets could be

accounted for by a diazacycloheptatriene which is frozen

in a non-inverting conformation, but the chemical shift

of both protons is more indicative of cyclopropyl than

allylic protons. The higher field doublet is assigned to

the endo proton which is shielded to some extent by the

azine linkage. The lower field doublet is assigned to

the exo proton which is deshielded by the phenyl rings

attached to the cyclopropyl ring videe infra).

At about this time preliminary x-ray crystallographic

results by Fritchie14 revealed that 23 indeed exists in the

diazanorcaradiene form rather than the diazacyclophepta-

triene form. A notable result of Fritchie's investigation

of 23 was that the cyclopropyl hydrogen occupies the exo

position and lies in the deshielding region of the phenyls

at C-l and C-6. Thus, in assigning only non-aromatic

proton as allylic rather than cyclopropyl on the basis of

chemical shift, Battiste2 was in error due to unforeseen

diamagnetic deshielding effects.






jpBr-C6gH4-- C6H4-p-Br







Heating 21 in pyridine caused noticeable broadening of

the NMR doublets at temperatures as low as about 90. The

signals for both methylene protons completely disappeared

at 150. Although time-averaging of the two methylene

protons was apparently occurring via ring inversion, no

time-averaged singlet for a rapidly inverting diazanorcara-

diene could ever be observed presumably due to decomposition

videe infra). Also, no signal for rearranged 21 could be

found.

On heating to as high as about 190 in either d5-nitro-

benzene or napthalene, decomposition of 21 to an unidenti-

fied red oil was observed. Further heating converted the

red oil to a yellow oil which could not be identified

after chromatography and spectral analysis.

Compound 22 showed temperature-dependent NMR behavior

similar to that exhibited by other diazanorcaradienes, such

as 24, with ester groups in the 2- and 5-positions.15 At

-3.50 the molecule is frozen in a non-exchanging form which

shows the expected NMR spectrum for the diazanorcaradiene

structure. The phenyls attached to the cyclopropane ring

show the expected ten-proton spike at r2.95. The ester

methyls, which are magnetically equivalent, appear as a

singlet at T6.35. Again, as in the NMR spectrum of 21,

the cyclopropyl protons show up as two widely separated

doublets at T6.37 (J = 5.7 Hz) and 9.0 (J = 5.7 Hz). Warm-

ing the NMR solution of 22 to 370 causes complete disappear-

ance of the cyclopropyl signals. The cyclopropyl doublets








coalesce at about 24 which is indicative of the phenyls

actually inhibiting the opening of the diazanorcaradiene

to the 5H-diazepine as the system 24 reported by Binsch and

Sauer's coalesces at between 5 and 16.




H3C02 / CO 2CH3
N-N

24

An attempt at thermally isomerizing 22 in refluxing

dioxane only produced small amounts of what is assumed to

be dimethyl 1,6-diphenyl-3,4-diazabicyclo[4.1.0]hept-2-en-

5-ol-2,5-dicarboxylate (25) mainly on the basis of its NMR

spectrum.

The NMR spectrum of 25 shows the expected broad singlet

at Tl.15 for the N-H proton, two multiplets centered at

2.95 and 3.6 integrating 8:2 for the ten aromatic protons,

a broad singlet for hydroxyl proton at 4.75, sharp singlets

at 5.58 and 6.18 for the nonequivalent methyl protons, and

an AB-quartet centered at 6.78 (J = 12.5 Hz) for the cyclo-

propyl protons.

No attempt was made at assigning the stereochemistry of

25. The mass spectrum of 25 gives the correct molecular

weight (364) but the cracking pattern in no way resembles

the mass spectral cracking pattern produced by the precursor

22. In the mass spectrometer one might have expected the

parent ion of 25 to lose a molecule of water to yield the







parent ion of 22, but apparently other processes are com-

petitive with loss of water and, hence, the cracking pattern

of 25 does not resemble that of 22. The addition of water

across the carbon-nitrogen double bond of diazanorcaradienes

is well-documented.5'16 An attempt at an authentic synthe-

sis of 25 was apparently a failure for unknown reasons.

Since of the two systems, 21 and 22, 22 should have

shown the greater propensity for rearrangement6 but did not

rearrange, no attempt other than the high temperature NMR

work was made at thermally isomerizing 21.

The thermal behavior of the simplest diazanorcaradiene,

6, which is 2 with no phenyls on the cyclopropyl carbons,

was also investigated. Refluxing 6 in xylene for 18 hours

produced nothing but tar and starting material.

Another system, 2,5,7-triphenyl-3,4-diazabicyclo[4.1.0]

hepta-2,4-diene (7), was examined. Refluxing in dioxane

for 132 hours yielded nothing but unidentifiable resin.




H 0 0
H& H :H H
H

0 0 \/ 0
N-N N-N

7 26

If 7 had rearranged to a 4H-diazepine via two concerted

1,5-hydrogen shifts, it would have rearranged to the known

26.17 Diazepine 26 was found to be stable under the condi-

tions used in the attempted rearrangement of 7.








From the above results it was concluded that three

phenyls on the cyclopropane ring were necessary before a

diazanorcaradiene will rearrange to a 4H-diazepine. How-

ever, it was still a mystery as to why systems 6, 7, 21,

and 22 did not rearrange to at least some small extent

if the rearrangement was taking place by way of a hydro-

gen shift mechanism.

Upon closer examination of the systems which do rearrange

and those which do not, it was noted that in the systems

which rearrange there is a phenyl ring over the azine link-

age. Thus, 2 is 1,2,5,6-tetraphenyl-endo-7-phenyl-3,4-

diazabicyclo[4.1.0]hepta-2,4-diene as shown in structure 27.

The compound 7 has the requisite phenyl in the 7-position,

but this phenyl is exo to the azine linkage as shown in

structure 28 since, in the absence of steric interaction

from substituents in the 1- and 6-positions, the phenyl

at C-7 prefers the exo position.





V-_ H NH r-

N7 N7
0 H
N N


0 0
27 28

The above observations led to the hypothesis that

perhaps the rearrangement is of the Cope ([3,3] sigmatropic)








type involving the endo-7-phenyl as illustrated in Scheme

5.



RH R H






NR N



,N
0 %
0
0 0i 0 0 H






Scheme 5

To test the idea of the Cope mechanism, the synthesis

of 2,5,7,7-tetraphenyl-3,4-diazabicyclo[4.1.0]hepta-2,4-

diene (29) was attempted since this system would have the

requisite endo-7-phenyl but no phenyls in the 1- and 6-

positions. Rearrangement of 29 by the pathway depicted in

Scheme 5 would lead to the diazepine 30.

The NMR spectrum of 30 should show an aromatic multiple

with the previously described deshielding of the ortho

protons of the phenyl at C-7. The ortho protons of the

phenyl at C-3 probably would not show any deshielding as

the phenyls at C-4 would impose steric restrictions forcing

the C-3 phenyl out of the plane of the azine linkage. The










H




N-N

30

vinylic protons should appear as an AB-quartet. The mass

spectrum of 30 should also be similar to that for 29 with

loss of benzonitrile as the base peak (see Chapter II).

During their investigation of the diazanorcaradiene 7,

Amiet and Johns4 reported that 7 could be synthesized in

low yield (7%) from trans-1,2-dibenzoyl-3-phenylcyclo-

propane (31) only by heating with hydrazine in ethanol for

long periods of time, whereas the cis isomer of 31 reacted

rapidly and almost quantitatively at room temperature. In

the present investigation it was found that 7 could be

produced in satisfactory yield (55.1%) from 31 at room

temperature if a catalytic amount of sodium hydroxide was

added to the mixture of 31 and hydrazine in ethanol. Pre-

sumably, the observed increase in yield is due to a rapidly

established base-catalyzed cis-trans equilibration as shown

in Scheme 6.



OHH H0 H 0

31 -\ 24 7
H1- 0 P 0 0 -H O
0-" I 1)I 2


Scheme 6







In view of the above observation, the synthesis of 29

was attempted by reaction of the known trans-l,2-dibenzoyl-

3,3-diphenylcyclopropane (32)18 with hydrazine in the

presence of sodium hydroxide in ethanol. At room tempera-

ture in ethanol, 32 and hydrazine in the presence of sodium

hydroxide showed no signs of reaction, i.e. no yellow color

or precipitate. On refluxing, the reaction mixture developed

a yellow coloration but then turned colorless again. The

colorless crystals isolated from the reaction mixture at

this point were not the desired 29, but an isomer C29H22N2

as determined from the mass spectrum and elemental analysis.

In the aromatic region,.the NMR spectrum of this iso-

meric compound 33 showed a multiple centered at T2.01

accounting for two protons and a multiple at 2.8 account-

ing for nineteen protons indicating only one phenyl with

ortho protons deshielded by an azine or otherwise electron-

withdrawing group. The only other feature of the spectrum

was a slightly broadened singlet at T4.31. Mostly on the

basis of the above NMR evidence the compound was identified

as 3,6-diphenyl-4-benzhydrylpyridaz.ine (33).

The phenyl in the 6-position is relatively free to

assume coplanarity with the pyridazine ring, thus account-

ing for the pair of deshielded ortho protons. However, the

phenyl in the 3-position is sterically crowded by the bulky

benzhydryl group in the 4-position which inhibits coplan-

arity with the pyridazine ring and, thus, all five protons

of the 3-phenyl are at approximately the same chemical








shift. The lone pyridazine ring proton is assumed to be

masked by the higher field multiple. The singlet at T4.31

is accounted for by the benzhydryl proton. The fact that

in the mass spectrum of 33 the parent ion is base peak is

in accord with a pyridazine carrying aromatic substituents.

Due to the development of a transient yellow color

during the formation of 33, it was not clear whether 29 is

initially formed and then converted into 33 under the influ-

ence of base (Scheme 7) or 32 was transformed via a base-

catalyzed ring-opening reaction into 2-benzhydryl-l,4-

diphenylbut-cis-2-ene-l,4-dione which would then react with

hydrazine to form 33 (Scheme 8).





NH
32- N- 2 4 base
32 -- 29
0 O 1






33 ------ H-
N-N' N-N

Scheme 7











32 OH 6


~81-
HH 0





NH







Scheme 8

When 29 was finally synthesized at a later date, it

was found to be insensitive to refluxing ethanolic sodium

hydroxide in the time interval necessary for the formation

of 33. Thus, it appears that a pathway similar to that in

Scheme 8 is in operation in the formation of 33 from 32.

The failure to obtain 29 by the simple route above

forced the adoption of a more elaborate synthetic scheme.

The scheme chosen was similar to that developed by Maier3

and is outlined below (Scheme 9) for this particular system.











AIC6H613 OH



34 35 N2H4






29 OU o
N-N'
H

36

Scheme 9

The known 3418 was synthesized in good yield (61%)

from diphenyldiazomethane19 and commercial maleic anhydride

simply by mixing the two reactants in benzene. The litera-

ture method'18'0 calls for mixing the two components and

refluxing in benzene.

Presumably due to polymerization, treatment of a ben-

zene solution of 34 with anhydrous aluminum chloride only

resulted in the formation of yellow, aqueous bicarbonate

soluble resin.

Addition of a benzene solution of 34 to anhydrous

aluminum chloride in benzene yielded 77.7% of a compound

tentatively identified as 3,3-diphenyl-trans-2-benzoylcyclo-

propanecarboxylic acid (37). Although the compound did not

give a correct elemental analysis, it did give a correct

mass spectral molecular weight (342) and, while the compound








was fairly insoluble, it gave an NMR spectrum which showed

only aromatic protons and an AB-quartet centered at T6.06.

The approximate coupling constant of 6 Hz for the AB-quartet

suggested the trans assignment for 37."l When 29 was

subsequently obtained, its AB-quartet for the cyclopropyl

protons showed a coupling constant of 8.0 Hz which is indica-

tive of a cis configuration.21

While the synthesis of 29 was in progress, a companion

effort was directed towards the synthesis of more compli-

cated, but just as physically useful systems such as 40 and

43. At first these systems appeared to be more readily

accessible than 29. The proposed synthetic routes are out-

lined below in Schemes 10 and 11. The requisite 2,3-dibenz-

oylbicyclo[2.2.1]hepta-2,5-diene (38)22 and 1,2-dibenzoylcy-

clohexa-l,4-diene (41)23 were known and easily obtained on

the multigram scale.




02C 2 0 2 4
38 -0 0 0 N




39 40


Scheme 10













SCN0 N2H4
41 2 0 N




42 43



Scheme 11

Unfortunately, both 38 and 41 were very unreactive

towards diphenyldiazomethane. On stirring for 24 days,

38 decolorized a solution of diphenyldiazomethane but

workup of the colorless material caused decomposition to

a purple substance which further decomposed to brown tar.

Refluxing 41 in benzene with a large excess of diphenyl-

diazomethane gave rise to copious amounts of a material

which is assumed to be benzophenone azine. Presumably the

low reactivity of 38 and 41 towards diphenyldiazomethane is

due to the cis arrangement of the benzoyl groups on the

double bond in both cases. This factor has been noted

previously.24

In an effort to bypass the critical synthetic inter-

mediates 35 and 36 of Scheme 9, an attempt was made at the

synthesis of 44 which, it was hoped, would add two moles of

phenyllithium to produce 29.



















On treatment with hydrazine 3,3-diphenyl-cis-cyclopro-

panedicarboxylic acid18 (45) was found to yield only water-

soluble material which, on addition of mineral acid,

regenerated 45. Presumably the water-soluble material is

the hydrazine salt of the acid rather than the hydrazide or

the desired 44.

Attempted addition of diphenyldiazomethane to maleic

hydrazide25 gave no identifiable products.

On refluxing the anhydride 34 with hydrazine in ethanol

for 60 hours, a new crystalline substance is produced. The

NMR spectrum, mass spectrum, and elemental analysis agreed

with structure 44 but, unfortunately, the spectra also

agreed with structure 46. The infrared, which shows a doub-

let rather than a singlet in the N-H stretch region, indi-

cates that structure 46 is probably the better choice.


N
NH2








Cyclic bisamide 44 or its isomer 46 gave no identifiable

products on attempted addition of phenyllithium under a

variety of conditions.

As a last resort, addition of phenylmagnesium bromide

to the anhydride 34 was attempted with success. Equimolar

quantities of the Grignard reagent and 34 produced 35 in

low yield (6.9%) when the reaction was carried out at room

temperature. Slightly better yields and cleaner product

were obtained either by adding the Grignard reagent to 34

in toluene at dry ice temperatures or by use of the diphenyl-

cadmium reagent.

Besides giving the correct molecular weight and elemental

analysis, the ketoacid 35 gave the expected NMR spectrum.

In the aromatic region, there is a low-field multiple cen-

tered at l1.9 integrating for two protons and a higher-

field multiple centered at 2.6 integrating for thirteen

protons. The Tl.9 multi plet is assumed to be due to the

ortho protons of the benzoyl phenyl. The T2.6 multiple

accounts for the remaining aromatic protons. The expected

AB-quartet at T6.48 integrates for.two protons. The coup-

ling constant of 8.0 Hz is that to be expected for cis

protons on a cyclopropyl ring of this sort.21 Ketoacid

35 also shows a carboxylic acid proton as a very broad,

almost undetectable singlet at about T-1.4.

The infrared (KBr pellet) of 35 shows no strong absorb-

ance for hydroxyl as would be expected for a carboxylic acid

hydroxyl. The carbonyl stretch of 35 is at 1730 cm-1 which








is more typical of a lactone than a free carboxylic acid.

The above is in accord with the observation that ketoacids

similar3 to 35 usually exist exclusively in a pseudo acid

form (structure 47) in the solid state.

In solution, ketoacids such as 35 tend to form an equi-

librium between free acid and psuedo acid.3





35 9$
HO 0O
47



On melting, 35 evolves carbon dioxide to yield some tar

and the known 1,4,4-triphenylbut-3-en-l-one (48).26 The

melting point and infrared carbonyl absorption were in close

agreement with that reported.26

The previously unreported NMR spectrum for 48 fits the

compound well. The aromatic region shows a two-proton mul-

tiplet centered at T2.17 and a thirteen-proton multiple

centered at 2.7. As with 35 videoe supra), the two aromatic

multiplets respectively account for the ortho protons of

the phenyl attached to the carbonyl and the remaining aro-

matic protons. The remaining portion of the spectrum shows

the expected vinylic triplet at T3.59 (J = 7.0 Hz) integrat-

ing for one proton and the expected methylene doublet at

6.21 (J = 7.0 Hz) integrating for two protons.











3S -A 0c
-CO 2


48

Stirring a solution of 35 and hydrazine hydrate in

ethanol for 24 hours gave the desired 2,7,7-triphenyl-5-

keto-3,4-diazabicyclo[4.1.0]hept-2-ene (36) as a white

crystalline precipitate. Even though 36 gave a correct

mass spectral molecular weight (338), an acceptable ele-

mental analysis could not be obtained. The analysis

suggested the presence of a'half mole of water of crystal-

lization. The infrared spectrum showed the expected

carbonyl stretch3 at 1670 cm-1.

Although fairly insoluble, an NMR spectrum of 36 could

be obtained. The amide proton appeared as a broad absorb-

ance at T1.9. As expected, the ortho protons of the phenyl

ring attached to the carbon-nitrogen double bond appeared

as a distinct multiple at about T2.0,with the remaining

aromatic protons appearing at higher field (2.40 3.16).

The two cyclopropyl protons appeared as the expected AB-

quartet at T6.88 (JAB = 8.0 Hz). The upfield half of the

quartet is split again into a pair of doublets by coupling

with the amide proton (HN) (JBN =.1.5 Hz, JAN = 0.0 Hz).




















36

The coupling between HB and HN finds precedent in the

literature27 and is not unexpected, especially when, upon

examination of a molecular model of 36, it is found that

HB and 1HN fit nicely into the well-known "W" pattern.28

There is no coupling between HA and HN as determined from

an HA-100 spectrum.

Addition of phenyllithium to 36 proceeded smoothly

producing 29 in moderate yield (47.2%). Diazanorcaradiene

29 analyzed correctly and gave a correct mass spectral

molecular weight (398) in addition to a reasonable frag-

mentation pattern.

In the aromatic region, the NMR spectrum of 29 dis-

played a four-proton multiple centered at Tl.8, a six-

proton multiple centered at 2.5, and two five-proton

singlets at 2.71 and 3.03. Presumably the lower field

nlultiplet is due to the ortho protons of the phenyls on

the deshielding azine linkage while the higher field

multiple again accounts for the remaining protons on the

2- and 4-phenyls. It is assumed that the higher field








aromatic singlet is due to the cyclopropyl phenyl over the

slightly shielding region of the azine linkage while the

lower field aromatic singlet is due to the other unshielded

cyclopropyl phenyl. The only other feature of the NMR

spectrum of 29 is a sharp singlet'at T6.58 integrating for

two protons. The singlet is due to the now equivalent

cyclopropyl protons.

Chemical evidence for structure 29 was provided by its

acid-catalyzed conversion into pyridazine 33 which had been

previously characterized.

In refluxing xylene over a 24-hour period, 29 gives rise

to a new, colorless, unknown isomer 49 which does not show

the properties usually exhibited by 4H-diazepines even

though it analyzes correctly and gives the correct molecu-

lar weight of 398.

The mass spectrum of 49 is completely different from

that of 29. The parent ion is base peak rather than the

parent minus benzonitrile ion which is only 3.5% of base

peak. The mass spectrum of 49 is quite featureless except

for peaks at 397 (21%) and 321 (14%).

The NMR spectrum of 49 is also quite featureless dis-

playing, as illustrated in Figure 1, only N-H at TO.18 and

aromatic multiplets centered at 2.7 and 3.2. The three NMR

signals integrated for one, fifteen, and six protons respec-

tively. That the signal at TO.18 is due to hydrogen

attached to nitrogen was proved by deuterium exchange with

heavy water which readily destroyed this signal.






































U

C"

r-4
F1









CT~

d-

(1)
0





25



















8





cI
0


'0o









I,
ec
'








- 8 \






o 0
'I



0-.\
Ct


s" p

0








Changing the NMR solvent from deuteriochloroform to

ds-pyridine altered the spectrum drastically as shown in

Figure 2, but gave no new information. Unchanged 49 could

be recovered after dissolution in pyridine.

Infrared and UV spectra gave no further useful informa-

tion as to the identity of 49.

It was fairly obvious that 49 was not the desired 4H-

diazepine 30. The possibilities left for 49 were all

C29H22N2 isomers which would show the observed spectro-

scopic properties of 49 and have a reasonable mechanistic

route for their formation.

The first possibility chosen for 49 was structure 50

which is shown along with a possible mechanism (Scheme 12).



H



N-N \ I


[1,5]

0^


Scheme 12




































.-


















0
0)

rP
U)









n
*r-

C7
*^1
P;











Structure 50 would fit the spectroscopic data if one

assumes sufficient deshielding of the vinylic and aliphatic

protons for them to appear in the aromatic region of the

NMR. However, 50 is a dihydropyridazine and, on the basis

of previous work,29 should readily oxidize to the fully aro-

matic pyridazine.

Oxidation of 49 with potassium dichromate in aqueous

acetic acid gave only some tar and a 41.3% recovery of start-

ing material. Extensive chromatography produced no more

material.

Oxidation of 49 with 1,2-dichloro-5,6-dicyano-l,4-

benzoquinone (DDQ) gave only dark green, difficultly soluble

material which, on chromatography over basic alumina,

yielded 87% recovered starting material which showed no

peak in the mass spectrum for 49 minus two hydrogens.

At this point it became fairly obvious that 49 does

not possess a dihydropyridazine structure or any other

structure which could be easily oxidized.

The next structure considered was structure 51 shown

below in Scheme 13.












29- N
N=N N

H




4i)



N



51


Scheme 13

There is no chemical evidence for or against 51. Once

again one must assume sufficient deshielding of the vinylic

proton to place it in the aromatic region in the NMR.

Other spectroscopic data do not really speak for or against

structure 51.

In the series 52, 53, and 54,30 the proton on the

pyrazole nitrogen appears in the NMR spectrum at 613.3,

10, and 7.22 as a broad singlet whose position is con-

centration dependent. The position of the N-H proton

of 49 is at about 69.8.










CH 3" CH3 CH3

/'c H--N H-NH

N= N- N-
CH3 CH3 CH3

52 53 54





H-, H-.N

N- N-r


55 56


For the two compounds 55 and 56,31 the UV spectra

respectively consist of ax = 256 nm (e = 33100) and

X = 250 nm (E = 15100). The UV maximum of 49 is at
max
237 nm (e = 28400) with inflections at 255 and 298 nm.

Possibly, steric interactions among the two phenyls and the

phenylstyryl group of 51 would cause a hypsochromic shift.

Since 49 was not the desired 4H-diazepine 30 and since

49 could not be identified, other means to determine the

mechanism of the diazanorcaradiene-diazepine isomerization

were sought.

The most direct and reasonable approach to this question

involved resorting to a suitably labeled system which was

known to rearrange and whose rearrangment product could be







identified by x-ray methods. The diazanorcaradiene 57 was

chosen as an appropriate system for study.
0
0 .^C6N.-1R

p-R-C6H H -Br-CeH4 C6H4-p-Br
0 0- N-N
path A 58
p-Br-C6H4 B- C6H4-p-Br-p-R





p.-Br-C6H4 \ / C6H4-p.-Br
N-N

59

Scheme 14

As outlined in Scheme 14, the 4H-diazepine 59 would

result if 57 underwent electrocyclic ring opening to the

corresponding 5H-diazepine followed by two consecutive supra-

facial concerted 1,5-hydrogen shifts (path B) as illustrated

previously in Scheme 4 for diazanorcaradiene 2.

The diazepine 58 could arise in several ways. First,

58 could result from the Cope-type mechanism previously

illustrated in Scheme 5 for the diazanorcaradiene 2. Also,

58 can arise by a Berson-Willcott Bones rearrangement32

whereby C-7 of structure 57 "walks" around the six-membered

ring to produce a 2,3-diazabicyclo[4.1.0]hepta-2,4-diene 60

which is unstable and opens up to the 4H-diazepine as

depicted in Scheme 15.











C614 ^--R


57 0 p-Br-C6H4


W.58


C6H4-p-Br


Scheme 15

The first step of Scheme 15 is concerted if the movement

of C-7 occurs with retention at C-7 as shown in structure 61

since this is a [1,5] sigmatropic change.12


p-R-C6H4


C6H4 -p-Br


Other nonconcerted mechanisms similar to the Bones

rearrangement may also be envisioned. One such mechanism

involving a dipolar (or diradical) intermediate is given in

Scheme 16.


C6H4-p-R


57 -w- p-Br-C6H4


C6H4-p-Br


i 60 4 58


Scheme 16








For the synthesis of 57, the problem reduces to the

preparation of triphenylcyclopropene with only the 3-phenyl

substituted with a group which can be observed by x-ray,

e.g. halogen, small aliphatic groups, etc. The above means

that no synthesis in which all three cyclopropenyl carbons

become equivalent chemically is satisfactory. Thus, synthe-

ses of sym-triphenylcyclopropene such as that developed by

Battiste are unsatisfactory.29

Recently, it was demonstrated by Longone and Stehouwer'3

that hydride ion can be added to the known diphenylcyclopro-

penyl cation to give exclusively 1,2-diphenylcyclopropene in

high yield. Thus, it was reasoned that an appropriately.sub-

stituted phenylmagnesium bromide could be added to the same

cation to give the desired substituted triphenylcyclopropene.

As a first attempt, p-chlorophenylmagnesium bromide was

added to diphenylcyclopropenyl perchlorate to produce, after

chromatography, a colorless solid whose NMR spectrum showed

only a singlet at T6.79 (sym-triphenylcyclopropene T6.833)

and an aromatic multiple. However, the aromatic multiple

integrated much too high and the compound tended to discolor

even in the absence of air and light. It was assumed that

the desired 3-(4-chlorophenyl)-1,2-diphenylcyclopropene (62)

had been obtained, but it could not be purified.

The same reaction as above was repeated with p-tolyl-

magnesium bromide. Good, clean product was obtained only

if the cation was added to the solution of the Grignard

reagent slowly. Rapid addition caused production of resinous








conglomerations which discolored the final product-as in

the case of cyclopropene 62.

The 3-(4-methylphenyl)-l,2-diphenylcyclopropene (63)

characterized as expected. Besides giving a correct ele-

mental analysis, 63 displayed the right mass spectral molecu-

lar weight (282). The NMR spectrum of 63 showed the expected

aromatic multiple centered at T2.64 integrating for fourteen

protons and two singlets at 6.83 and 7.76 integrating for

one and three protons respectively. The T6.83 signal is

typical for a triphenylcyclopropene cyclopropenyl proton as

was mentioned above. The T7.76 signal is, of course, due to

the methyl group.

If the Grignard reagent had added so as to give the

isomeric cyclopropene 64, a one-proton singlet at ca.

T2.634 rather than 6.83 would have been anticipated.

CH3





9H

64

The infrared spectrum of 63 displayed the typical

cyclopropene carbon-carbon double bond stretch at 1830 cm-1

(sym-triphenylcyclopropene 1820 cm-1 34). The UV spectrum

of 63 was also very useful as it showed the maxima charac-

teristic of a sym-triphenylcyclopropene at 332.5 nm








(E = 23000), 315 nm (E = 28000), 305 nm (s, e = 22000),

302 nm (infl.), and 228 nm (e = 32000). For comparison,

the UV spectrum of sym-triphenylcyclopropene itself in

ethanol consists of maxima at 330 nm (e = 24200), 313 nm

(E = 29000), and 228 nm (E = 30600).35

Cycloaddition of 63 with 3,6-bis(4-bromophenyl)-

1,2,4,5-tetrazine (65)6 produced the expected 2,5-bis-

(4-bromophenyl)-7-(4-methylphenyl)-1,6-diphenyl-3,4-

diazabicyclo[4.1.0]hepta-2,4-diene (66). The diazanorcara-

diene analyzed correctly and gave a correct mass spectral

molecular weight (644). The diazanorcaradiene also gave a

reasonable mass spectral fragmentation pattern which is

discussed in Chapter II.

The NMR spectrum of 66 simply consisted of a twenty-

two-proton aromatic multiple centered at T2.93, a one-

proton singlet at 5.03 for the cyclopropyl proton, and a

three-proton singlet at 7.83 for the methyl group. For

comparison purposes, the cyclopropyl proton of the analogous

diazanorcaradiene 2 appears at T4.98.2

The thermal rearrangement of 66 in refluxing xylene

proceeded more rapidly than was anticipated and, as a

result, a much lower yield of the 4H-diazepine was obtained

than was expected due to decomposition. Presumably, the

methyl group of the substituted phenyl aids in the decompo-

sition of the 4H-diazepine 67 to the corresponding pyrroles

and benzonitriles. Diazepine 67 gave the anticipated analyti-

cal and spectral data as recorded in the Experimental Sec-

tion (Chapter V).








Table II

Bond Distances and Their Estimated Standard Deviations in
Diazepine 67

o
Atoms Distance (A) e.s.d.a

Br(l) C(E4) 1.91 0.01
C(E4) C(E5) 1.38 0.01
C(E5) C(E6) 1.40 0.01
C(E6) C(E1) 1.37 0.01
C(E1) C(E2) 1.39 0.01
C(E2) C(E3) 1.38 0.01
C(E3) C(E4) 1.37 0.01
C(E1) C(5) 1.50 0.01
C(5) N(l) 1.31 0.01
N(l) N(2) 1.39 0.01
N(2) C(1) 1.29 0.01
C(1) C(A1) 1.47 0.01
C(A1) C(A2) 1.40 0.01
C(A2) C(A3) 1.38 0.01
C(A3) C(A4) 1.37 0.01
C(A4) Br(2) 1.91 0.01
C(A4) C(A5) 1.36 0.01
C(A5) C(A6) 1.41 0.01
C(A6) C(A1) 1.39 0.01
C(1) C(2) 1.52 0.01
C(2) C(B1) 1.53 0.01
C(B1) C(B2) 1.39 0.01
C(B2) C(B3) 1.43 0.01
C(B3) C(B4) 1.37 0.01
C(B4) C(Me) 1.54 0.01
C(B4) C(B5) 1.41 0.01
C(B5) C(B6) 1.37 0.01
C(B6) C(B1) 1.40 0.01
C(2) C(3) 1.52 0.01
C(3) C(C1) 1.50 0.01
C(C1) C(C2) 1.40. 0.01
C(C2) C(C3) 1.41 0.01
C(C3) C(C4) 1.38 0.01
C(C4) C(C5) 1.36 0.01
C(C5) C(C6) 1.42 0.01
C(C6) C(C1) 1.38 0.01
C(3) C(4) 1.34 0.01
C(4) C(D1) 1.48 0.01
C(D1) C(D2) 1.42. 0.01
C(D2) C(D3) 1.40 0.01
C(D3) C(D4) 1.40 0.01
C(D4) C(D5) 1.43 0.01
C(D5) C(D6) 1.40 0.01
C(D6) C(D1) 1.39 0.01
C(4) C(5) 1.48 0.01


estimated standard deviation.








Table III

Bond Angles and Their Estimated Standard Deviations in
Diazepine 67


Atoms Angle (deg.) e.s.da


Br(l) C(E4) C(E5) 117.8 0.5
Br(l) C(E4) C(E3) 119.5 0.5
C(E4) CCE5) C(E6) 117.1 0.7
C(E5) C(E6) C(E1) 121.3 0.6
C(E6) C(El) C(E2) 119.8 0.6
C(E1) C(E2) C(E3) 120.2 0.6
C(E2) C(E3) C(E4) 118.9 0.7
C(E3) C(E4) C(E5) 122.7 0.7
C(5) C(E1) C(E2) 118.6 0.6
C(5) C(E1) C(E6) 121.6 0.6
C(4) C(5) C(El) 119.7 0.6
C(4) C(S) N(1) 125.7 0.6
N(1) C(5) C(E1) 114.5 0.6
C(S) N(l) N(2) 121.4 0.5
N(1) N(2) C(1) 121.3 0.5
N(2) C(l) C(Al) 115.9 0.6
N(2) C(1) C(2) 123.9 0.6
C(2) C(l) C(A1) 120.0 0.6
C(A1) C(A2) C(A3) 120.3 0.7
C(A2) C(A3) C(A4) 119.0 0.7
C(A3) C(A4) Br(2) 118.6 0.6
C(A3) C(A4) C(A5) 123.2 0.7
C(A5) C(A4) Br(2) 118.2 0.6
C(A4) C(A5) C(A6) 118.0 0.7
C(A5) C(A6) C(A1) 120.6 0.7
C(A6) C(Al) C(A2) 118.9 0.6
C(1) C(Al) C(A6) 119.2 0.6
C(1) C(Al) C(A2) 121.9 0.6
C(l) C(2) C(3) 102.8 0.5
C(l) C(2) C(B1) 115.7 0.6
C(3) C(2) CCB1) 116.0 0.6
C(B1) C(B2) C(B3) 121.1 0.7
C(B2) C(B3) C(B4) 119.0 0.7
C(B3) C(B4) C(Me) 121.2 0.7
C(Me) C(B4) C(B5) 119.1 0.7
C(B3) C(B4) C(B5) 119.7 0.7
C(B4) C(B5) C(B6) 121.4 0.7
C(B5) C(B6) C(B1) 120.0 0.7
C(B6) C(B1) C(B2) 118.9 0.6
C(2) C(B1) C(B2) 120.8 0.6
C(2) C(B1) C(B6) 119.9 0.6
C(2) C(3) C(C1) 116.8 0.6
C(2) C(3) C(4) 120.1 0.6
C(4) C(3) C(C1) 123.0 0.6












C(C1)
C(C2)
C(C3)
C(C4)
C(CS)
C(C6)
C(3)
C(3)
C(3)
C(5)
C(3)
C(4)
C(4)
C(D1)
C (D2)
C (D3)
C(D4)
C(D5)
C (D6)


Atoms

C(C2)
C(C3)
C(C4)
C(C5)
C(C6)
C(C1)
C(C1)
C(C1)
C(4)
C(4)
C(4)
C(D1)
C(D1)
C(D2)
C(D3)
C(D4)
C(D5)
C(D6)
C(D1)


S-able- -11e I -(continued)

Angle (deg.)

C(C3) 120.2
C(C4) 119.3
C(C5) 121.0
C(C6) 120.5
C(Cl) 119.1
C(C2) 119.8
C(C2) 120.3
C(C6) 119.9
C(5) 120.7
C(D1) 114.0
C(Dl) 125.3
C(D2) 121.5
C(D6) 120.7
C(D3) 121.5
C(D4) 118.8
C(D5) 121.3
C(D6) 117.8
C(D1) 122.9
C(D2) 117.7


e.s.da

0.7
0.8
0.8
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.6
0.6
0.6
0.7
0.7
0.8
0.7
0.7
0.6


estimated standard deviation.



The x-ray analysis of 67, which is described in the

Experimental Section, revealed that the rearrangement of 66

follows path A given in Scheme 14 above. An ORTEP-generated

model of 67 is shown in Figure 3. A table of bond lengths

is given in Table 2 and a table of bond angles is given in

Table 3.

At this point, all that can be said in the absence of

further data is that diazanorcaradienes containing one phenyl

on each cyclopropyl position rearrange to 4H-diazepines by

one of the mechanisms discussed above involving movement of

an entire carbon rather than hydrogen shifts. Once again a

system whose rearrangement appeared to be simple on the

surface turned out to be quite complex on closer examination.




























PI

r-4







rc











s o







,a (3)
CdV









0 r-
P 4








00
















04-
I N4
























01-






















.r.4
9r3
(d







ca i-
.rT


















E-






41




Cn'








4 U

















oI U U








Sco



to
u







In connection with the further reaction of the diazepine

systems to produce pyrroles and benzonitriles, some ground-

work on the mechanism of this fragmentation was carried out.

As was mentioned at the beginning of the chapter,

diazepines which result from the high temperature reaction

of sym-triphenylcyclopropene and tetrazines substituted

with groups other than unsubstituted phenyl decompose at

high temperatures into mixtures of pyrroles and benzoni-

triles as shown in Scheme 2. Thus, in an as yet unspeci-

fied manner (see Chapter II), not only the groups originally

on the tetrazine ring but also the 1- and 2-positions of the

cyclopropene become involved in the diazepine decomposition.

It was also of interest to ascertain whether or not the

4-phenyl of the diazepine also becomes involved in the

decomposition. Toward this end 1,2,5,6-tetraphenyl-7-

(4-methylphenyl)-3,4-diazabicyclo[4.1.0]hepta-2,4-diene

(68) was prepared. Diazanorcaradiene 68 showed the

expected properties which, as demonstrated in the Experi-

mental Section, are quite similar to those for 66.

When 68 was decomposed in the injector port of an

analytical gas chromatograph with the column at such a

temperature that benzonitrile and p-tolunitrile are

separable, p-tolunitrile was detected and identified

solely on the basis of its relative retention time. The

results are summarized in Scheme 17. It should be stressed

that these results on the decomposition of 68, while excit-

ing, are still only tentative.















2400
68


H3C _-CN + O'CN +


pyrroles


Scheme 17













CHAPTER II

MASS SPECTRAL CORRELATIONS


Introduction

The frequent observation that mass spectral and thermal

behavior closely parallel each other for certain compounds

is one of the more intriguing aspects of mass spectrometry.36

It will be the main purpose of this chapter to demonstrate

briefly that the thermolytic reactions of Scheme 2 in

Chapter I are correlated by the mass spectral behavior of

the diazanorcaradienes which rearrange to 4H-diazepines and

to attempt to enlighten the mechanism of the 4H-diazepine

decomposition.

As shown in Scheme 2, the thermolysis of diazepines

such as 70 yields two pyrroles, benzonitrile, and acetoni-

trile. In the absence of further data, such conversions







H 3 C CH3
N-N

70


may be rationalized generally as in Scheme 18.










R 4,



RR R R R
N-N N=N








I I
N-N





R H H H








RCN H R
N-N N' N-N

R R C

or











RRN R







0CN RCN

R = CO2CH3

= Ctt3

= p-H3C-C6H4


Scheme 18








Results and Discussion

The most obvious mass spectral feature of the diaza-

norcaradienes which undergo thermal rearrangement is their

marked similarity to the mass spectra of their respective

4H-diazepines. As examples, the mass spectra of diazanor-

caradienes 2 and 66 are plotted in Figures 4 and 6. The

mass spectra of the corresponding 4H-diazepines 3 and 67

are given in Figures 5 and 7 respectively. Except for the

intensities of some peaks, the mass spectra of 2 and 3 and

of 66 and 67 are almost superimposable.

From the above one can arrive at one of three conclu-

sions the parent ion of the diazanorcaradiene rapidly

rearranges to the parent ion of the respective 4H-diaze-

pine, the parent ion of the 4H-diazepine isomerizes to the

parent ion of its precursor diazanorcaradiene, or both the

diazanorcaradiene and 4H-diazepine parent ions convert into

a common intermediate which gives rise to the observed

fragmentation pattern.

The mass spectra of all diazanorcaradienes examined,

whether they have been observed to rearrange or not, show

several similar fragmentations as illustrated in Scheme 19.

Table IV gives the intensities for the observed fragmenta-

tions of the diazanorcaradienes studied. In those diaza-

norcaradienes not bearing carbomethoxy or methyl groups in

the 2- and 4-positions, loss of benzonitrile or substituted

benzonitrile is base peak. All diazanorcaradienes, regard-

less of substitution or ability to rearrange, show a fairly








intense (2 to 99% of base peak) peak for parent ion (M+)

minus nitrogen. Corresponding to this loss of nitrogen


RCN
R ---


R H


-N*
N2


1:


H


R N R


RI RI

R




R: ,-R
R / R


denotes metastable for this fragmentation

Scheme 19

peak is a flat-top metastable peak which indicates that the

nitrogen is lost from the parent ion with the release of a

small amount of kinetic energy.37

From the above observation that the mass spectra of 4H-

diazepines resemble the general diazanorcaradiene mass

spectrum, it is tempting to assume that in the mass spectro-

meter 4H-diazepines derived from diazanorcaradienes revert

to their precusor diazanorcaradienes or an ion common to



















*H


I-q




C) C1 W) a)C:
1 0 0 '0 0 1
1 00 0 1
I H4 I








0 i i


a)
o>P I










00

-q I-l


2; dP dp dp dp dP dP o P dp

M' m V) Ln n C4 t






U 4
, dP dP dp dpo dP d'p o\dp
0\'0 CRO 0\0 H .0\ Oa
Ho r- 00 r--4 %D 00 M Hn
r-l4 C4 ri- i-q


ba
II U
r I bo -I U




ILll = I SL 1p
II C ISL II II II
d ii -I

it II "

II p m ii II II.


I-I m cM o


II II II II II II II II



C'-H C D) r-4 C") H W
N- r-q H (" %.0


SbO


*-I H .M c r-
P4 "0 0
0 : P4
N O
Cd P a) I




41 0 4-

0 O 0 0a

o C- a- 0 o
M 0U




4 ( '. 0L4


wJ cd r, rH P.



0 0
O i.i n
1- *) ra Q'p
:3 Cd C 0 P4 a)




a) M- c c

o a ) a) Ud




,d 0 a o 0
0 wd P4 r
0) HH 0 )o
.r 1-H a Cd -C



0 U 0U)
O p- *, 0t
+ Q) a) 4ui
CdO 5 (1

"0 Cd a) 0
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ot &. 6) lc 4
.H *H U)1 N 4-
tQ U)c; 0) cd i



O r- X a)
0 cd H )- L4
H Cd r- U)
S >- a 4-) d P4
0d 0 (D

I- 0 -H r NB +
ai Cd a) c0 -


a) P a)* r
N a) 0o a) Cd
Cd r p 0 r-r%

0 Cd 0d

Iu E-4 U d ) V)

a ) t Ip




*l NP -H 4



a) a)o *H C








Cd rfl pH U








both. This would lend some credence to the first step of

Scheme 18. However, the mass spectra of diazepine 26 and

diazanorcaradiene 7 are also quite similar even though, as

demonstrated in Chapter I, thermally 7 does not isomerize

to 26. It has also been shown that apparently 26 does not

decompose into pyrroles and benzonitrile on thermolysis.38

Thus, in the absence of further information, all that can be

said about the diaza species which give rise to pyrroles on

thermal decomposition of 4H-diazepines derived from diaza-

norcaradienes is that the mechanism of Scheme 18 or

something similar is not precluded by mass spectral

observations.

Although the mass spectra of rearrangeable diazanorcara-

dienes and, of course, the corresponding 4H-diazepines give

no real information on the mechanism of diazepine decomposi-

tion to pyrroles, for the most part the mass spectra do

follow the thermal decomposition process quite closely.

The thermal decomposition data for the four diazepines

that have been studied6 are tabulated in Table V. The mass

spectra of the four diazepines or closely related compounds

are given in Table IV.

All diazepines formed from .the'rearrangement of diazanor-

caradienes show intense mass spectral peaks for pyrroles

formed by electron-impact-induced decomposition of M.. At

least as far as low-resolution mass is concerned, the

pyrroles formed in the mass spectrometer correspond to those

formed by the thermal process of Scheme 18. The base peak







in the mass spectrometer is always M. minus benzonitrile or

substituted benzonitrile except when the azine linkage is

substituted with carbomethoxy or methyl groups. It will be

noted that thermally 3,7-bis(p-tolyl)-4,5,6-triphenyl-4H-

1,2-diazepine (73), which is related to 71 decomposes into

an approximately equimolar mixture of pyrroles resulting

from loss of benzonitrile and p-tolunitrile. In the mass

spectrometer diazepine 71 loses approximately three times as

much p-iodobenzonitrile as benzonitrile. The above facts

may be rationalized by considering that thermally 73 (or 71)

can lose nitriles RCN and R'CN only from bicyclic forms

similar to 8 (see Preface and Scheme 18),whereas in the

mass spectrometer the diazepine can lose RCN from the open

form or the bicyclic form but can lose R'CN only by isomeriz-

ing through the bicyclic form. It will be again noted that

the diazepine 26 does not result from the thermal isomeriza-

tion of a diazanorcaradiene nor has it been possible to

thermally decompose it into benzonitrile and pyrrole, but

yet, in the mass spectrometer, loss of benzonitrile is base

peak.








Table V
6
Thermal Decomposition Data for Some 4H-Diazepines


Diazepine -0CN -RCNa


3b 100%
11 >98% ----
73 49% 51%d
70 67% 33%
aR is the group originally on the 3- and 7-positions
of the diazepine. The other three positions of the
diazepine are substituted with phenyla. Can only
lose benzonitrile. CNone detected. A small amount
of unidentified liquid (not benzonitrile or 2-tolu-
nitrile) was detected in this decomposition.


The mass spectra of diazepine 11 and its related

diazanorcaradiene 10 (Figure 8) show 71% and 65% peaks for,

respectively, loss of methyl cyanoformate and loss of

benzonitrile from the parent ion. The base peak corres-

ponds to what may be formally described as the decarboxyla-

tion product of the pyrrole formed by loss of benzonitrile

from the parent ion as depicted in Scheme 20. Thermally,

diazepine 11 converts exclusively into dimethyl 3,4-

diphenylpyrrole-2,5-dicarboxylate, which is the end result

of loss of benzonitrile from II.6 Again the loss of methyl

cyanoformate from the parent ion of 11 may be due to

fragmentation from the open diazepine form as opposed to









H H

H E N EE CH 3
E E
N N ; e E I


m/e 438 m/e 335 m/e 291

E = CO2CH3


Scheme 20

fragmentation from a bicyclic form and thus have no thermal

analogy.

In the mass spectrum of the diazanorcaradiene related

to 70 (72), loss of acetonitrile from the parent ion is base

peak but loss of benzonitrile from the parent ion gives only

a 3% peak! Thermally the diazanorcaradiene 72 converts into

70 only with difficulty relative to cases where the diaza-

norcaradiene azine linkage is substituted with phenyls or

carbomethoxy groups. Also with difficulty, 70 thermally

converts into a 2.17:1 molar mixture of, respectively,

2,5-dimethyl-3,4-diphenylpyrrole and l-methyl-2,3,4-tri-

phenylpyrrole.6 Thus, thermally, loss of benzonitrile is

the predominant pathway. The combination of the loss of

acetonitrile from the unrearranged form of the diazanor-

caradiene 72 in the mass spectrometer and the difficulty

with which the diazanorcaradiene rearranges to 70 may be

used to rationalize the unusually low abundance of the loss

of benzonitrile from the parent ion in the mass spectrum








of the diazanorcaradiene 72. At the time of this writing

no mass spectrum of 70 was available.

As a further complication to the diazepine decomposi-

tion problem, it was shown tentatively in Chapter I that,

on thermolysis, diazanorcaradiene 68 presumably reacting

via diazepine 69 yields tolunitrile in addition to the

expected benzonitrile.

The mass spectrum of 68 shows a peak for the loss of

tolunitrile from the parent ion as depicted in Figure 9.

The loss of tolunitrile from the parent ion is supported by

a metastable peak but, unfortunately, the metastable can

also be accounted for by loss of methyl from the parent

minus benzonitrile ion. A similar problem arises in the

interpretation of the mass spectrum of diazanorcaradiene

66 and its related diazepine 67 (Figures 6 and 7).

In closing this chapter it will be noted that the

mass spectra of all diazanorcaradienes and diazepines

examined show a P-I peak of 5-28% intensity (see Table IV).

In all cases except when the azine linkage is substituted

with methyl groups the P-I intensity is only 5-16%. It is

assumed that the hydrogen lost is the one at C-7 in

diazanorcaradienes and C-4 in diazepines except when the

azine linkage is substituted with methyl groups, which opens

the possibility of loss of hydrogen from one of the methyl

groups to form an ion such as 74.





.54


H3C':-\ /--CH
H3 C N=N, C 2

74


Although some of the driving force for loss of a

hydrogen radical from the parent ion is conversion from the

odd-electron M. to the even electron P-l ion, perhaps

another driving force may be formation of the aromatic

diazatropylium cation 75. It is noteworthy that in the

mass spectrum of cycloheptatriene, which is known to

easily convert into the aromatic tropylium cation, base

peak is loss of hydrogen radical.39 The diazatropylium

problem will be discussed more fully in Chapter IV.


























C)





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CHAPTER III

CYCLOPROPYL CONJUGATION IN HETEROAROMATIC SYSTEMS


Cyclopropyl Conjugation

The phenomenon of cyclopropyl conjugation is quite well

known40 and has been extensively investigated in both 'the

ground state and excited state of many molecules.

Closs and Klinger41 observed that with decreasing

temperature the ortho protons in cyclopropylbenzenes show

increased shielding. The increased shielding was attributed

to increased population of the bisected, electronically

favorable conformation 76.






76



Electron diffraction42 and infrared spectroscopy43

also have been employed to detect cyclopropyl conjugation

in unsaturated molecules which are-in their ground state.

Kosower and Ito44 found that the excited states of

ketones are stabilized by the presence of a cyclopropyl

ring alpha to the carbonyl carbon if the geometry is correct.

In ketone 77 the geometry is correct for cyclopropyl








conjugation as the cyclopropyl ring is in the bisected

configuration. The geometry is far from ideal in ketone

78. Interaction in the excited state was found to lower


0 0






77 78


the excited state of 77 by 7-8 kcal/mole relative to the

excited state of 78.

As a general rule, it has been found that, in the

absence of geometric factors, weak cyclopropyl conjugation

is a consequence of poor electron-withdrawing ability of

the unsaturated group to which the cyclopropane ring is

attached.45 In other words, the greater the electron

demand of the molecule to which the cyclopropane ring is

attached, the greater will be the conjugation of the cyclo-

propane ring with that molecule. Also, it has been shown

that the extent of cyclopropyl conjugation is a function

of geometry only if the group interacting with the cyclo-

propane ring is sufficiently electron-withdrawing.45

The compounds to be investigated, 3,6-dicyclopropyl-

1,2,4,5-tetrazine (79) and 3,6-dicyclopropylpyridazine

(80), are both similar to monocyclopropylbenzene studied

by Closs and Klinger41 in that the cyclopropyl rings are







both bonded to an aromatic six-membered ring. There are

definite interesting differences though.

Tetrazine 79 contains four nitrogens in the aromatic

ring which, accordingly, should enhance cyclopropyl conjuga-

tion with the tetrazine ring due to the great electron-

withdrawing power of the tetrazine ring. Also, unlike

cyclopropylbenzene, the tetrazine ring of 79 carries no

hydrogens and, thus, there are negligible steric factors.

The only complication is that, assuming the dicyclopropyl-

tetrazine is completely in the bisected form, two conforma-

tions are possible which may complicate the NMR spectrum

of 79. The top view of the hypothetically possible syn and

anti conformations is illustrated below as structures 81 and

82 respectively.

H H H





H

81 82


The pyridazine 80 should exhibit cyclopropyl conjuga-

tion similar to that of tetrazine 79 but reduced somewhat

due to replacement of two nitrogens by less electron-

withdrawing C-H groups i.e. the conjugation in 80 should be

intermediate between that of cyclopropylbenzene and

tetrazine 79. Also, in the case of 80, steric effects again








are operative as in cyclopropylbenzene since the pyridazine

ring has a hydrogen in both the 4- and 5-positions. Assum-

ing the bisected form for 80 the syn rotamer 83 should be

favored over the syn rotamer with both cyclopropyl methylene

functions interacting with the hydrogens of the pyridazine

ring or either of the trans rotamers.


H H


H H




83


Synthesis

The synthesis developed by Abdel-Rahman et al.0 is

only one of the many synthetic schemes known for the forma-

tion of dihydrotetrazines which can be oxidized to their

respective s-tetrazines.46'47 The synthesis is quite simple

in that it involves merely refluxing a mixture of hydrazine

hydrate, a nitrile, flowers of sulfur, and ethanol for a

period of one to three hours. As an example, use of benzoni-

trile in the Abdel-Rahman synthesis yields 85% dihydro-3,6-

diphenyl-1,2,4,5-tetrazine. Aromatic nitriles generally

produce dihydrodiaryltetrazines in high yield, whereas alkyl

nitriles give only low yields of the respective dihydro-

dialkyltetrazines.








Besides being simple, the Abdel-Rahman synthesis

represents a route to dihydrotetrazines under non-acidic,

non-forcing reaction conditions. Thus, the synthesis is

ideal for preparation of the intriguing 3,6-dicyclopropyl-

1,2,4,5-tetrazine (79) which can be converted into the

equally interesting 3,6-dicyclopropylpyridazine (80) by

known routes.1

Of itself the Abdel-Rahman synthesis presents an

interesting mechanistic problem. While synthesizing large

quantities of 3,6-diphenyl-l,2,4,5-tetrazine (1), about a

2.5% isolated yield of the well-known 2,5-diphenyl-l,3,4-

thiadiazole (84)48 was obtained as a side product in this

work.






N-N

84

No mention of 84 was made by Abdel-Rahman. The only

reported work towards enlightening the mechanism of the

dihydrotetrazine forming reaction was to ascertain that

phenylthiohydrazide, under the reaction conditions, does

not afford dihydrodiphenyltetrazine. Abdel-Rahman found that

under the reaction conditions employed phenylthiohydrazide

reacts to form, not dihydrodiphenyltetrazine, but rather

"something else."'0 What the "something else" is was not