PART 5
THE PHGTDREARRANGEMENT 0F
BECYCLGEZLEIQCTADIENONES
AND RELATED ALCOHGLS

PART I!
THE PHOTOISOMERIZATION 0F
1(2H) -NAPHTHALENONES

fhesis for the Degree of Ph. D.
MICHIGAN STATE UNQVERSITY
ROGER K. MURRAY, JR.
1968

[fittmb

Michigan 5“”
Univcmty

 

This is to certify that the

thesis entitled
PART I
THE PHOTOREARRANGEMENT OF THE BICYCLO[2 .2 .2] -
OCTADIENONES AND RELATED ALCOHOLS

PART II

THE PHOTOISOMERIZATION OF 1(2H)-NAPHTHALENONES
presented bg

Roger K. Murray, Jr.

has been accepted towards fulfillment
of the requirements for .

Ph.D. degree in Chemlstry

_, (7’? .A‘ «1‘ ”Obi "Li/.a/ ’(

Major professor

 

 

i

D December 20, 1968
ate

 

0-169

uw’ {NJ .11‘,-_"_._-

M

1’
—

if nun-once In “ i
am a sour ~
noux amnsnv me. i

I LIBRARY BINDERS

YIW‘ ' i

 

 

HE PHCTC

THE

In the
3f \‘arisusj

ifiYESti

LQ
J
r

Irrad

[2'2-213ct

Cemene de

ABSTRACT

PART I
THE PHOTOREARRANGEMENT OF BICYCLO[2.2.2]OCTADIENONES
AND RELATED ALCOHOLS
PART II

THE PHOTOISOMERIZATION OF 1(2H)-NAPHTHALENONES

BY

Roger K. Murray, Jr.

In the first part of this thesis the photochemistry
of variously substituted bicyclo[2.2.2]octadienones was
investigated.

Irradiation of ether solutions of hexamethylbicyclo-
[2.2.2]octadienones Q2 and g2 provided high yields of the

benzene derivatives g1 and §§J respectively.

 

 

R
hv
ether
R
g2, R = COZCH3 g;, R = COZCH3

§Zx R = C6H5 §§x R = CeHs

 

. , |
Tne pnetoel;
efficiently

Similar

 

[2.2 .210ctad
naphthalene,

Emever , ace

‘31 and 48
fICm the a

\

2 Roger K. Murray, Jr.
The photoelimination of dimethylketene from Ea proceeded
efficiently even at -100°.
Similarly, irradiation of a solution of benzobicyclo-
[2.2.2]octadienone fig in ether gave 1,2,3,4-tetramethyl—
naphthalene, $1, and a benzobicyclo[3.2.0]heptadiene, fig;

However, acetone-sensitized irradiation of 46 gave not only

47

48

 

 

o
/

0’

22, o
\h">47+48+. ¢
acetone ‘”” ’“V

 

21 and 2§J but also ketone fig; The ketonic product isolated
from the acetone—sensitized irradiation of benzobicyclo[2.2.2]-

octadienone gg' has been identified as 22; This result

hv
————_—’>
acetone

   

 

b nzobicyci
:ively. Ac
provided a
are the pr:

_a a (ii-~-

 

3 Roger K. Murray, Jr.
requires that the photoisomerization of fig to ketone fig,
occurs from the triplet gig 1,2-acyl migration and not by
a di—w-methane rearrangement.

A most unusual substituent effect was observed in the
photochemistry of anti: and syn—1,3,3,4,7,8—hexamethyl—5,6-
benzobicyclo[2.2.2]octa-5,7—dien-2-ols, 22 and gi, respec—
tively. Acetone-sensitized irradiation of antifalcohol 22’
provided a 3:2 mixture of two alcohols, 22 and 22; These
are the products expected from the photoisomerization of 92'

via a di-w-methane rearrangement. However, similar irradia—

 

OH
OH
/ I I h v > + I”
\\ acetone 'H
90 92 93

m m rw

tion of syn-alcohol 9} gave only a single alcohol, 22;

Hydrogen bonding or charge transfer interaction with the

HO H
/ I / hV
\\ acetone

91 99

 

 

phstoisore
[3 .1 .0] he:

purpose 0:

4 Roger K. Murray, Jr.
oxygen may be the factors which control the course of this

photorearrangement.

A determination of the mechanisms operative in the
photoisomerization of naphthalenone 121 to benzobicyclo—
[3.1.0]hexenone 122 and of 122 to naphthalenone 122 was the

purpose of the second part of this thesis.

 

 

O O O
I
CO H > O». M 00
121 123 124

my

Irradiation of an ether solution of 2,2,4—trimethyl-
1(2H)-naphthalenone, 122x prepared by the oxidation of
1,2,4-trimethylnaphthalene with peroxytrifluoroacetic acid-
boron fluoride etherate in methylene chloride, provided

3,4,4—trimethyl—1(4H)-naphthalenone, 148. A detailed

. O
H
__h_£___,
O. ether 00
H
136 148

W

consideration of the mechanisms possible for the photoisomer-
ization of a 1(2H)-naphthalenone to a benzobicyclo[3.1.0]-

hexenone shows that the isolation of 148 from the photolysis

:f 136 re:
WV

121 to be:

M

rechanism

Phot:

csntaininc

'tsnd-cro.

Lewis

lfifii-napi
ethyl-1,2
aCid‘er3:

4‘ethyl—3

.o’f the pa
be: .. .

that tl‘e

‘1

313?; the E

mph thaler

5 Roger K. Murray, Jr.
of 1§§ requires that the photorearrangement of naphthalenone
lgl’to benzobicycloketone lgg'proceeds by a "bond-crossing"
mechanism.

Photolysis of a hexane solution of naphthalenone £21
containing dimethyl amine gave 122; Irradiation of a solu-
tion of naphthalenone 121 in methanol afforded naphthalenone
124'2i3_bicycloketone 122; These results suggest that the
"bond-crossing" mechanism for the photoisomerization of
121 to 122 does not involve a ketene intermediate.

Irradiation of an ether solution of 4—ethyl—2,2-dimethyl—
1(2H)-naphtha1enone, 124” prepared by the oxidation of 4-
ethyl-l,2—dimethy1naphtha1ene with peroxytrifluoroacetic
acid-boron fluoride etherate inmethylene chloride, gave

4-ethyl—3,4—dimethyl—1(4H)—naphthalenone, 156. An examination

0
hv ,

154 156

W W

 

of the possible mechanisms for the photorearrangement of a
benzobicyclo[3.1.0]hexenone to a 1(4H)-naphtha1enone shows
that the isolation of lgg'from the photolysis of 122 requires
that the photoisomerization of benzobicycloketone lgg to

naphthalenone 124 occurs via a 1,2-alkyl migration.

 

THE PHOTC

 

THE P

 

 

ir.

IL

PART I

THE PHOTOREARRANGEMENT OF BICYCLO[2.2.2]OCTADIENONES
AND RELATED ALCOHOLS

PART II

THE PHOTOISOMERIZATION OF 1(2H)—NAPHTHALENONES

BY

Roger K.JMurray, Jr.

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY
Department of Chemistry

1968

 

.—_.-—_
.* k......._—_—

Q ~. ~

‘ ,\

. n

. v_ ~.

The as

to Professc

 

and guide:
|
Apprec

Health fgr
t3 Septembe

Appre=
versity fQ
1964 throu
March, 196
cial Supp;
September
Office iD‘

ACKNOWLEDGMENT

The author wishes to express his sincere appreciation
to Professor Harold Hart for his enthusiasm, encouragement
and guidance throughout the course of this study.

Appreciation is extended to the National Institutes of
Health for a pre—doctoral fellowship from September, 1967
to September, 1968.

Appreciation is also extended to Michigan State Uni-
versity for a Graduate Teaching Assistantship from September.
1964 through June, 1966 and from September, 1966 through
March, 1967, to the National Science Foundation for finan—
cial support from June, 1966 to September, 1966 and from
September, 1968 to December, 1968, and to the Army Research
Office (Durham) for financial support from March, 1967 to

September, 1967.

ii

 

'EE PHCT

mmonucms:
RESULTS Am

A.

 

  
 

 

The D
SIG-d
one ;

bicyc

The c
5,6-t
and E
octa-

The 1
Hexa;
2‘One

CYCL

The ,
Hexa
2—01

EXPERIMENT

A.

B.

G839
Gene

IIIE

Qica

1'30
'VV

IIIE
phe;
Die,

TABLE OF CONTENTS

Page
PART I

THE PHOTOREARRANGEMENT OF BICYCLO[2.2.2]OCTADIENONES
AND RELATED ALCOHOLS

INTRODUCTION . . . . . . . . . . . . . . . . . . . . 2
RESULTS AND DISCUSSION . . . . . . . . . . . . . . . 10

A. The Direct Irradiation of 1,3,3,4,7,8éHexamethyl—
5,6-dicarbomethoxybicyclo[2. 2. 2]octa- -5, 7—dien-2-
one (30) and 1, 3, 3, 4, 7, 8—Hexamethyl- -5, 6-diphenyl-
bicyclo[2. 2. 2]octa— —5, 7—dien-2-one (32) . . . . 10

B. The Direct Irradiation of 1,3,3,4,7,8-Hexameth l-
5,6-benzobicyclo[2.2.2]octa-5,7-dien—2—one (46'
and 3,3,7,8-Tetramethyl-5,6-benzobicyclo[2.2.2]—
octa—5,7-dien-2-one (56) . . . . . . . . . . 14

C. The Photosensitized Rearrangements of 1,3,3,4,7,8-
Hexamethyl- -5, 6-benzobicyclo[2. 2. 2]octa- 5, 7-dien-
2—one (46) and 3, 3, 7, 8-Tetramethyl— —5, 6—benzobi-
cyclo[2. 2. 2]octa—5, 7-dien- 2-one (56) . . . . . 21

D. The Photosensitized Rearrangements of 1,3,3,4,7,8-
Hexamethyl-5,6-benzobicyclo[2.2.2]octa-5,7-dien-

2—ols (92 and 91) . . . . . . . . . . . . . . 28
EXPERIMENTAL . . . . . . . . . . . . . . . . . . . . 39
A. General Procedures . . . . . . . . . . . . . . 39
B. General Photolysis Procedures . . . . . . . . 39

C. Irradiation of 1,3,3,4,7,8—Hexamethyl—5,6—
dicarbomethoxybicyclo[2.2.2]octa—5,7-dien-2-one
(32) in Diethyl Ether . . . . . . . . . . . . 41

D. Irradiation of 1, 3, 3, 4, 7, 8-Hexamethyl- 5, 6-di—
phenylbicyclo[2. 2. 2]octa- -5, 7 —dien- 2-one (32) in
Diethyl Ether . . . . . . . . . . . . 41

iii

 

TABLE OF C01?

E. A LOW
1,3,3,

octa-d

F. Photo;
bicyc;
Dieth;

G. Photo;
benzci
Dieth;

I. Irrad;
cyclc[
Ether

J° Irrad;
bicycl

 

 

 

K- Irradi
515-be
In Ace

Irradj
516-be
in Ace

Irrad;
Cycle}

REd‘dc 1
CYClo
thhi1

TABLE OF CONTENTS (Continued)

E.

Page

A Low Temperature Study of the Photolysis of
1, 3, 3, 4, 7, 8-Hexamethyl- -5, 6-diphenylbicyclo[2. 2. 2]-
octa—5, 7-dien- 2—one (32) . . . . . . . . . . . . 43

Photolysis of 1, 3, 3, 4, 7, 8-Hexamethyl-5,6-benzo-
bicyclo[2. 2. 2]octa- -5, 7-dien-2-one (26) in
Diethyl Ether . . . . . . . . . . . . . . . . . 44

Photolysis of 4-Methyl—g3-1,3,3,7,8-pentamethyl-5,6-
benzobicyclo[2. 2. 2]octa— 5,7 ~dien-2-one (103) in
Diethyl Ether . . . . . . . . . . . . . . . . . . 45

Photolysis of 7—Methylag3-1,3,3,4,8-pentamethyl-
5, 6-benzobicyclo[2. 2. 2]octa- -5,7-dien-2-one (104)
in Diethyl Ether . . . . . . . . . . . . . . . . 47

Irradiation of 3,3,7,8—Tetramethyl-5,6-benzobi—
cyclo[2.2.2]octa-5,7-dien-2—one (66) in Diethyl
Ether . . . . . . . . . . . . . .-. . . . . . . . 47

Irradiation of 1, 3, 3, 4, 7, 8—Hexamethyl- -5, 6—benzo-
bicyclo[2. 2. 2]octa— —5, 7—dien— —2-one (46) in Acetone. 5O

Irradiation of 4—Methyl- -d3 -1, 3, 3, 7, 8-pentameth l—
5, 6—benzobicyclo[2. 2. .2]octa— —5, 7-dien-2- -one (Z6,
in Acetone . a . . . . . . . . . . . . . . . 52

5, 6-benzobicyclo[2. 2. .2]octa- -5, 7 —dien-2-one (

Irradiation of 7-Methyl- -d —1, 3, 3, 4, 8-pentameth -
78)
in Acetone . . . . . . . . . . . . . . . . . 53

Irradiation of‘3,3,7,8-Tetramethyl-5,6-benzobi-
cyclo[2.2.2]octa—5,7—dien—2—one (66) in Acetone. . 53

Reduction of 1,2,4,4-Tetramethyl-6,7—benzotri—
cyclo[3.330.02'8]oct-6-en—3-one (16) with
Lithium Aluminum Hydride . . . . . . . . . . . . . 54

Irradiation of 1, 3, 3, 4, 7, 8-Hexamethyl- -5,6-benzo-
bicyclo[2. 2. 2]octa- -5, 7-dien- anti- 2-ol (66) in
Acetone . . . . . . . . . . . . . . .1. . . . . 56

Oxidation of 1,2,3,3,5,8-Hexamethyl-6,7-benzo-

tricyclo[3.3.0.02:8]oct—6-en-anti-4-ol (62)
with Chromium Trioxide-Pyridine . . . . . . . . . 61

iv

 

TABLE OF CC?

Q. Oxide
tricy
Chro:

R. Reduc
tricyE
Lith;

S. Irrad
bicyc
Acetc

T- Oxide
cycl;

Chror

U~ Redu:
Cycl:
Lithl

summy

IEJTRODUCTIQ

 

RESLITS AND

MQCha
B The p

napht
C The p

1.123
D.

COan

TABLE OF CONTENTS (Continued)

Q. Oxidation of 1,2,4,4,5,8-Hexamethyl-6,7-benzo—
tricyclo[3.3.0.02I8]oct-6—en-anti-3-ol (93) with
Chromium Trioxide—Pyridine . . . . . . I“? . .

R. Reduction of 1,2,4,4,5,8-Hexamethyl—6,7-benzo-
tricyclo[3.3.0.02I8]oct-6-en-3—one (68) with
Lithium Aluminum Hydride . . . . . I“? . . . .

S. Irradiation of 1, 3, 3, 4, 7, 8-Hexamethyl- -5,6-benzo—
bicyclo[2. 2. 2]octa- -5, 7-dien—syn n—2-ol (21) in
Acetone . . . . . . . . . . . . . . . .

T. Oxidation of 1, 2, 3, 3, 5, 8-Hexamethyl-6,7—benzotrié
cyclo[3. 3. O. 02. I8]oct-6- -en-s yn n-4-ol (22) with
Chromium Trioxide-Pyridine‘. . . . . . . . . .

U. Reduction of 1, 2, 3, 3, 5, 8-Hexamethyl-6,7-benzotri—
cyclo[3. 3. O. 02. 8]oct— 6- en-4—one (69) with
Lithium Aluminum Hydride . . . . . . . . . . . .

SUMMARY . . . . . . . . . . . . . . . . . . . . . .

PART II

THE PHOTOISOMERIZATION OF 1(2H)-NAPHTHALENONES

INTRODUCTION . . . . . . . . . . . . . . .
RESULTS AND DISCUSSION . . . . . . . . . . . . . . .
A. Mechanistic Considerations . . . . . . . . . . .

B. The Photorearrangement of 2, L 4—Trimethyl-1(2H H)-
naphthalenone (136) . . . . . . . . . . . . .

C. The Photorearrangement of 4—Ethyl- 2, 2- -dimethyl—
1(2H)-naphthalenone . . . . . . . . . . . . .

D. Conclusion . . . . . . . . . . . . . . . . . . .

Page

61

62

63

65

67

68

72
78

78

84

100

108

 

TABLE OF CC.

EXPERIMEN T};

A. Irrad
bicyc‘

B. Prepa
1. 1
2.

C. The 0
1 p

a
b

D. Irrad
one (

E- Irrad
napht

F- Irrac
napht

G’ P163);
1158
W»
1.

2.

H' Th61
(1..
t¢3§
1.

I. IIra
“aph

J.

 

 

TABLE OF CONTENTS (Continued)

EXPERIMENTAL . . . . . . . . . . . . . . . . . . . .

A.

Irradiation of 1,5,6,6~Tetramethyl—3,4-benzo-
bicyclo[3.1.0]hexen-2-one (123) in Diethyl Ether

Preparation of 1,2,4-Trimethylnaphtha1ene

1. 1-Chloromethyl— —3, 4-dimethylnaphthalene
2. 1, 2, 4-Trimethylnaphtha1ene . . . . .

The Oxidation of 1,2,4—Trimethylnaphtha1ene

1. Product Identification

a. 2,2,4-Trimethyl-1 2H)-naphtha1enone (136)

b. 1,1,4—Trimethyl—2 1H)-naphthalenone

Irradiation of 2, 2, 4—Trimethyl— —1(2H) —naphthalen-
one (136) in Diethyl Ether . . . . . . . . .

Irradiation of 2,2,3,4-Tetramethyl-1(2H)-
naphthalenone (121) in Hexane—Dimethyl Amine .

Irradiation of 2,2,3,4—Tetramethyl-1(2H)-
naphthalenone (121) in Methanol . . . .

Preparation of 4-Ethyl- -1, 2— —dimethylnaphthalene
(158) . . . . . . . . . . . .

1. 1—Acetyl-3,4-dimethylnaphthalene
2. 4-Ethyl—1,2-dimethylnaphtha1ene

The Oxidation of 4—Ethyl— —1 ,2-dimethylnaphtha1ene
(158).. . . . . . . . . . . . . . . . .

1. Product Identification . . . . . . . . . .

a. 4—Ethyl- -2, 2-dimethyl—1(2H)-naphthalen-

one (154) . . .
b. 4- -Ethyl-%1 1-dimethyl- 2(1H)—naphthalen-
one (159) . . . . . . .

Irradiation of 4—Ethyl-2,2-dimethyl-1(2H)-
naphthalenone (154) in Diethyl Ether

Irradiation of 4—Ethyl—2,2-dimethyl-1(2H)-
naphthalenone (154) in Trifluoroethanol .

vi

Page
109

109
110

110
110

111
113
113
113
114
115
116 '
117
117

118

119
120

120
121

121

123

 

TABLE OF cc:

SUMMARY

LITERATURE

 

TABLE OF CONTENTS (Continued)

Page
SUMMARY . . . . . . . . . . . . . . . . . . . . . . . 124

LITERATURE CITED . . . . . . . . . . . . . . . . . . . 126

vii

 

II.

III.

 

TABLE

II.

III.

LIST OF TABLES

 

Page
The ultraviolet Spectra of some bicyclic
dienes . . . . . . . . . . . . . . . . . . 17
The infrared and ultraviolet spectra of
1(2H)-naphthalenones 121 and 136 . . . . . 89
The infrared and ultraviolet spectra of
2(1H)-naphthalenones 122 and 142 . . . . . 90

viii

 

HGUE

1.

(

I

(J!

10.

11.

12,

13,

 

A dE'
or g;
anger

A de'
and I

rang:

A de‘
(or I
rang:

Nmr
213-1

Nmr s
benz;

Nmr s
617‘}

Nmr 5
benz:

Nmr 3
bEHZI

 

Nmr J
beaz:

Nmr;
benz:

Nmr :
meth:
4~Ql

Nmr
bEQZ

A me
Prod

LIST OF FIGURES

FIGURE Page

1. AA detailed mechanism for the formation of fig,
(or £2) from gg'via a di-v-methane photorear-
rangement . . . . . . . . . . . . . . . . . . . 24

2. A detailed mechanism for the formation of 22'
and gé'from 92'via a di-v-methane photorear-
rangement . . . . . . . . . . . . . . . .'. . 35

3. A detailed mechanism for the formation of 92'
(or 100) from 91 via a di-w-methane photorear-
rangement . . . . . . . . . . . . . . . . . . 38

4. Nmr spectrum (CC14) of 1,4,4,5,6,7-hexamethyl-
2,3-benzobicyclo[3.2.0]hepta-2,6-diene (4g). . 46

5. .Nmr spectrum (CC14) of 4,4,6,7-tetramethyl-2,3-
benzobicyclo[3.2.0]hepta-2,6-diene (§§) . . . 49

6. [Nmr spectrum (CC14) of 1,2,4,4,5,8-heXamethy1-
6,7-benzotricyclo[3.3.0.02:8]oct-6-en-3-one (fig) 51

7. Nmr spectrum (CC14) of 1,2,4,4-tetramethyl-6.74
benzotricyclo[3.3.0.02r8]oct—6-en—3-one (1Q).. 55

2,4,4—tetramethy146,7-

8. Nmr spectrum (CC14) o ,
.0.0 ' ]oct-6-en-anti-3-ol (22) 57

benzotricyclo[3.3

9. Nmr spectrum (CCl4

) o 1,2,3,3,5,8-hexamethy146,7-
benzotricyclo[3.3.0.0 8

. ]oct-6-en-anti-4-ol (92) 59
10. .Nmr spectrum (CC14) of 1,2,4,4,5,8-hexamethy146,7-
benzotricyclo[3.3.0.02'3]oct-6-en-anti-3-ol (92) 60

11. .Nmr spectrum (CC14, no TMS) of 1,2,3,3,5,8-hexa-
methyl-6,7-benzotricyclo[3.3.0.02:3]oct-6-en-sxn-
4-ol(gg).................. 64

12. Nmr spectrum (CC14) of 1,2,3,3,5,8-hexameth l-6,7-
benzotricyclo[3.3.0.02I8]oct-6-en-4-one (Qg' . 66

13. A mechanism for the formation of the oxidation
products of 1,2,4-trimethylnaphthalene . . . . 91

ix

 

TIE PHD ".

 

PART I

THE PHOTOREARRANGEMENT OF BICYCLO[2.2.2]OCTADIENONES

AND RELATED ALCOHOLS

 

During
interaction

phatochemica

 

interest. A
of .enocycl‘l
The ult

C1iSPeISion a

 

0f irrunsat‘.
able intErac
EI‘i‘dOlele; b
can be attri

finding P‘Or

slightly d1:

3f the n N

F: .
I a gIVEn

fer
‘ence in e

carbonTarb

INTRODUCTION

During the past decade investigations concerning the
interaction of formally nonconjugated chromophores in
photochemical transfonmnjons have attracted considerable
interest. A case in point is the photochemical behavior
of monocyclic and bicyclic 5,7—unsaturated ketones.

The ultraviolet spectra (1,2) and optical rotatory
dispersion and circular dichroism curves (2—4) of a number
of fi,y-unsaturated ketones indicate there is a consider-
able interaction between the w—electron‘systems of the
5,7-double bond and the carbonyl group. This interaction
can be attributed (1,4) to the overlapping of the non-
bonding p-orbital of the oxygen atom with the w-orbitals
of the ground state of the fi,y-double bond (which has only
slightly different energy) and results in an intensification
of the n —> w* absorption of such unsaturated ketones.
For a given geometrical arrangement, the smaller the dif-
ference in energy between the w —> w* transition of the
carbon-carbon double bond and the n -> w* transition of
the carbonyl, the more intense will be the mixed n-—> W*
transition (5). Of course the borrowing of intensity by
the n —> w* transition from the v —> v* transition re-
duces the intensity of the latter. The chemical consequences

2

 

afthis ele:
photochemica
msaturated

Irradia
results in C.
version to ti
phase irrad;

|
1.3-butadiezi

t{Elan tum e f fi

h

 

 

tion of .
an

mercuIy are
In Str;
WES have hi

1 -
.2 ac“ m.

k .
Stones

e .
irradia.

3
of this electronic interaction are demonstrated in the
photochemical reactions of monocyclic and bicyclic B,y-
unsaturated ketones.

Irradiation of the n -> w* band of 3-cyclopentenones
results in decarbonylation and highly efficient con-
version to derivatives of 1,3-butadiene. Thus the vapor-
phase irradiation of 3-cyclopentenone, 1} provides only

1,3-butadiene and carbon monoxide, with a

00 hv > CH2=CHCH=CH2 + co

1.

 

quantum efficiency near unity for the formation of

these products and constant over the temperature range of
60-1900 (6). Similarly, irradiation of a cyclohexane solu—

tion of Z'With the unfiltered radiation of a high-pressure

of + o*
‘\//
. D

 

2. ~
Inercury arc gives dienes 3 and 4 (7).

In striking contrast to these results, 3-cyclohexen-
canes have been observed to photochemically rearrange with
]-.2-acy1 migration to provide isomeric conjugated cyclopropyl

kertones. Thus Williams and Ziffer have reported (8) that

time irradiation of a Efbutyl alcohol solution of 5 through

 

a pyrex fll

ysis of (+

CODditions

mathIlene-A

 

ReCent
C‘Jclohepten
Principal F
mCItocyCl-l c
arrangerfiemt
transformt
state (10_]

dimethyl—3.

4

a Pyrex filter affords glin greater than 60% yield. Photol-

 

O
Si 6

ysis of (+)-17B—hydroxyoestr—5(10)-en-3—one, Z, under similar

OH OH
hV
—-->
O
I

z. 0 g

conditions gives the single isomer 17fi-hydroxy—5a,10a-
methylene—A-noroestran-3—one, § (9).

Recent investigations of the photochemistry of 3—
cycloheptenones and 3-cyclooctenones have shown that the
principal photochemical transformation of medium—sized
monocyclic B,y-unsaturated ketones involves 1,3—acyl re-
arrangement and migration of the allylic double bond. This
transformation appears to occur yia the n-——> v* singlet
state (10-12). Irradiation of an ether solution of 2,2—
dimethyl-3-cycloheptenone, 2x through a Corex filter pro—
vides 12'as the only volatile photoproduct° This rearrange-
ment is photochemically reversible (10). Paquette (11) and

Crandall (12) have also reported that irradiation of

 

3-cycloocte
vinylcyclo‘r.

main photol

 

g, 19.

3-cyclooctenone,‘££, in a variety of solvents yields 2-
vinylcyclohexanone, 12/ and 5,7-octadienal,‘£§, as the

main photolysis produCts. The experimental data (12) re-

0

 

 

 

 

   

11 14 12

CH2 = CHCH = CH(CH2)35-H
13’
quire a photoequilibrium between ketones 11 and 12 and an
irreversible process leading to aldehyde 12; Consequently
the photorearrangement of ll’has been explained in terms
of a primary Norrish type I process leading to the biradical
12“ followed by transannular rebonding to provide 12 or
hydrogen abstraction to give 13’
Ultraviolet irradiation of bicyclic ketones in solu-
tion has produced a variety of photochemical reactions (13).
IHowever, several recent reports suggest that B,y—unsaturated
Tbicyclic ketones undergo a general photochemical reaction

that involves cleavage of the carbon-carbon bond located

 

allyl to U“
sequent don:
classic stuc

methy Ibicyc.

 

methy lbicyc.

3n irradiat

tion of eit

3?.
d 29, 6r.

SpEQtrum

$

6
allyl to the double bond and a to the carbonyl with sub—
sequent double bond migration and recyclization. In a
classic study Buchi and Burgess found (14) that 1,4,4-tri-
methylbicyclo[3.2.0]hept-6—en-2-one, 15, and 4,4,6-tri-

methylbicyclo[3.2.0]hept-6-en—2-one, 16/ are interconverted-

 

 

”" hv
V V
15 16

m rw

 

 

 

 

on irradiation with ultraviolet light. Similarly, irradia-

tion of either pure 11 or 1§ provides a photostationary

 

13‘
<

 

 

 

 

 

17
- 18

state mixture containing 70% 1§ and 30% 11 (15). Erman and
Kretschmar have also shown that cyclic enones of type 12'

and gg'are interconverted on irradiation with a broad

 

 

Spectrum mercury arc lamp (16). As a result of these

Studies, it may be concluded that the product distribution

 

CV

 

7
of the photostationary state cannot be related to the rela-
tive thermodynamic stability of the products, but rather
is a function of the photochemical properties of the mole-
cules considered (14,16).

In the photochemical rearrangements of other B,y—unsat—
urated bicyclic ketones the reverse photorearrangements have
not been observed, apparently due to competition from more
efficient reactions of the photoproducts. Thus ultraviolet
irradiation of dehydronorcamphor, 21“ in a variety of sol—

vents provides bicyclo[3.2.0]hept-2-en-7-one, 22/ as the

//
- 90 hv / + CH2=c=o
I > _ » >

21 22

 

 

 

 

 

 

initial photoproduct (17). However, upon further irradia-
tion gg'is converted into cyclopentadiene and ketene (17,18).
Cookson has also examined the photochemistry of a number of
substituted bornenones and found them to photorearrange to
isomeric bicyclo[3.2.0]hept-2-en—7-ones, which with longer
irradiation dissociate into ketene and the appropriately
substituted cyclopentadienes (19).

Most recently two reports have appeared concerning re-
lated systems in which the pi-electrons of more than one
B,y-double bond can interact with the carbonyl group.

Kende has found that irradiation of a solution of 6,7-benpo-

bicyclo[3.2.2]nona-3,6,8—trien-2-one, 23” in acetonitrile

1
‘0'

."

 

 

.‘.
Our-

.0 1:

me:

.
Y‘
c-J

—o
4

*4.

8

However, it can be shown spectroscopically

 

 

that ketone 24 is not present in the photolysis solution
during the irradiation, but can be instantly generated
therein by the addition of base. Thus it is proposed that
the primary step in the photoisomerization is the rearrange—
ment of gg'to the diolefinic ketone 22“ with ultimate isom—
erization t1) 24 taking place during the work—up procedure.

Similarly, irradiation of 22 gives 21 (21).

 

C]. O O
/ C) c
. no .
> .
l
26 27

m m

Previous studies in this laboratory (22,23) have pro-
vided a number of variously substituted bicyclo[2.2.2]octa-
5,7-dien-2-ones, 22” gig the addition of acetylenic deriva-
tives to the readily available (24) hexamethyl-2,4-cyclo—
hexadienone, 28” Such bicyclo[2.2.2]octadienones as gg'pro-

Vide a rigid bicyclic system in which the pi—electrons of

 

O

0 /
R-CEC-R > R

A I /

Zfi. 22.

both 5,y—double bonds can interact equally with the carbonyl
group. The presence of such interaction zus reflected in
the enhanced n -—> n* absorption maxima (22) in the ultra-

violet spectra of 32 and the benzo derivative 42; Part I

O
0*
O \,,

300

i
max

5 373

 

of this thesis examines the photochemical consequences of
this electronic interaction in variously substituted bicyclo-

[2.2.2]octadienones.

 

 

3;.

RESULTS AND DISCUSSION

A. The Direct Irradiation of 1,3,3,4,7,8-Hexamethyl—5,6-
dicarbomethoxybicyclo[Z.2.2]octa-5,7-dien—2-one (@g)
and 1,3,3,4,7,8-Hexamethyl-5,6-diphenylbicycloL2.2.2]-
octa-5,7-dien-2-one (ggj.

 

 

The bicyclo[2.2.2]octa-5,7-dien—2-ones desired for this
study were prepared by the addition of acetylenic derivatives
to hexamethyl-2,4—cyclohexadienone, g§’(24). As previously
reported by Kakihana (22), refluxing 28 and dimethyl acety-
lenedicarboxylate in xylene gave a high yield of 1,3,3,4,7,8-
hexamethyl-5,6-dicarbomethoxybicyclo[2.2.2]octa-5,7-dien—2-

one, 32; Similarly, 1,3,3,4,7,8—hexmethyl-5,6—diphenyl-

o
> COZCH3
I /
COZCH3
28 30

W rw

 

Ibicyclo[2.2.2]octa-5,7—dien—2-one, 32/ was prepared by

Iheating 2§,and diphenyl acetylene at 2000(22).

©-CEC-¢
> ¢
A
J1
¢
gt: 3 2

’W

 

10

11
Irradiation of a 1% ether solution of 32 through a
Corex filter with a Hanovia L 450-W lamp proceeded smoothly
and efficiently to provide an 80% yield of dimethyl 3,4,5,6-

tetramethylphthalate, 31“ which was identified by comparison

0

4’
COZCH3

COZCH3

 

I / >
ether

30 3.1.

(mp, ir and nmr spectra, Rt) with an authentic sample (22).

Irradiation of 32 under identical conditions gave an 83%
yield of 3,4,5,6-tetramethyl—1,2-diphenylbenzene, §§x which

was also identified by comparison (mp, mixed mp, ir and nmr

¢
¢ hv
I ether >
/ 4’ ‘p
32 £9.

spectra) with an authentic sample (22). Dimethylketene, 34/

formed during the reaction was trapped as isobutyranilide,

22/ by the addition of aniline to the crude photolysate.

0
CH3 _ H /CH3
‘::C=c=0 $_Efla__> ¢—NH-C--C::-H
CH3 CH3
34 £2.

 

 

com

{rm-
5 v-

fiY‘

0‘. i

,.
'V!

1-;

4.,

“L‘

12

Two alternative mechanisms can be suggested for these
conversions: (a) direct photoelimination of dimethylketene
from the bicyclo[2.2.2]octadienone in either a concerted
or stepwise fashion (The implications of a concerted photo-
elimination of dimethylketene are discussed in Section B.),
or (b) photorearrangement of the bicyclo[2.2.2]octadienone
gg'to cyclobutanone gz'and/or 38/ which then eliminates di-

methylketene to give 32; Path b has ample precedent, for

 

   

39

(W

the principal photochemical transformation of bicyclic
Biy-unsaturated ketones involves 1,3—acyl rearrangement and
migration of the allylic double bond (16). For example,
ultraviolet irradiation of dehydronorcamphor, 21/ provides

bicyclo[3.2.0]hept-2-en—7-one, 22: as the initial

30 QT)

 

 

13
photoproduct (17). Similarly, irradiation of bicyclo[3.3.1]-
non-2—en—9—one, 22/ provides a photoequilibrium mixture of

42'(27%) and bicyclo[5.1.1]non-2-en-9-one, 41,(62%) (16).

j 4"

4O 41

The photoelimination of ketene from a cyclobutanone (step 2
of path b) has also been reported. Thus the principal

photoprocess observed in the irradiation of a benzene solu—
tion of 42 is the photoelimination of ketene and the forma—

tion of 43 (25). Similarly, irradiation of 1—phenyl-3,4,4-

 

 

hv
>
benzene

 

 

H3CO

 

trimethylbicyclo[3.2.0]hept-2-en—7-one, 42” gave cyclopenta-
diene gé'and ketene.

Ph
0 Ph
\ _

44 45

 

5;

any

14

A low temperature study of the photolysis of the di-
phenylbicyclo[2.2.2]octadienone 32 was carried out in an
attempt to help differentiate between the two alternative
mechanisms. The apparatus used in this study was designed
by Dr. John Griffiths of this laboratory. A solution of 32'
in 2-methyltetrahydrofuran was irradiated for short inter—
vals at -1000 in a sodium chloride cavity cell. 'Monitoring
the photolysis by infrared showed the immediate appearance
of a sharp intense absorption at 2135 cm-1 which increased
in intensity as the irradiation was continued. The intensity
of the carbonyl absorption of 32 decreased during the irradia-
tion. The absorption at 2135 cm—1 is attributed to the
formation of dimethyl ketene, 32; Ketene intermediates de-
tected in a similar manner by Hart and Griffiths (26) and
Chapman and Lassila (27) show infrared absorptions in the
region 2145-2050 cm-1

These observations are consistent with path a I.£;S;'
the direct photoelimination of dimethylketene from the
ibicyclo[2.2.2]octadienone. For path b to be plausible,
the elimination of dimethylketene from the cyclobutanone

intermediates 3} and/or 38 must be efficient at -100°.

13. The Direct giradiation of 1,3,3,4,7,8-Hexamethyl-5,6-
benzobicyclo[2.2.2]octa-5,7—dien-2-one (22) and 3,3,7,8-

Tetramethyl-5,6-benzobicyclo[2.2.2]octa-5,7—dien-2-one (56)

As previously reported (23,28), 1,3,3,4,7,8-hexamethyl-

5,6-benzobicyclo[2.2.2]octa-5,7—dien—2-one, 42“ was prepared

15

by the reaction of benzyne with hexamethyl—2,4-cyclohexa~

dienone, 28 (24). Similarly, the reaction of benzyne with
O
Q

 

 

as 46

3,4,6,6-tetramethyl—2,4-cyclohexadienone, £2} (29) gives
3,3,7,8-tetramethyl-5,6-benzobicyclo[2.2.2]octa—5,7—dien-

2—one, 56 (22). The direct irradiation of 42 and 52 was

H 0 H ’0
H
252. ggH

investigated in order to study the influence on the photo—

 

chemistry of the bicyclo[2.2.2]octadienones when one of
the two carbon-carbon double bonds of the bicyclo[2.2.2]-
octadienone system belonged to a fused aromatic ring.
Irradiation of a 1% ether solution of 46,through a
Corex filter with a Hanovia L 450-W lamp, when allowed to
proceed to 86% conversion of 42/ provided an 82% yield of
1,2,3,4-tetramethylnaphthalene, 41” and a 13% yield of
1,4,4,5,6,7—hexamethyl—2,3-benzobicyclo[3.2.0]hepta-2,6-

diene, 48; 1,2,3,4-tetramethy1 naphthalene was identified

16

 

//o
-—-*“’ Q /
o m 00 +0 .
\
46 47 48

NV W I‘w

by comparison with an authentic sample. The elemental
analysis and mass spectrum (parent peak at m/e 226) of 48;
indicated that it was formed by the elimination of carbon
monoxide from 46, The nmr spectrum of 48 consisted of sing-
lets at T 8.95 (3H), 8.83 (3H) and 8.75 (6H), quartets at

T 8.53 and 8.50 (3H each, J = 1.2 Hz), and a singlet at

 

T 3.05 (4H, aromatic protons). Structures 42 and 52 are
also consistent with these data. However, examination of
‘ 0‘

22. 50

Table I indicates that these compounds can be differentiated
by their ultraviolet spectra. As benzonorcaradiene, 51, is
structurally analogous to 52, and 4,4-dicyano+2,3-benzobi-
cyclo[3.2.0]hepta-2,6-diene, 52/ is similarly related to

48” the ultraviolet spectra of 51 and 54 should provide good
models for the expected ultraviolet spectra of 52 and 4g,
respectively. Previously reported bicyclo[3.2.0]hepta-2,6-

dienes show only end absorption in the ultraviolet region.

17

Table I. The ultraviolet spectra of some bicyclic dienes.

 

 

 

 

 

 

N CN
/
0‘ ' ' '
‘ \

51(31) 2%(32) 24.133)
kmax’ mu (log 6) xmax’ mu (5) kmax’ mu (5)
306 (3.02) 282 (580) 273 (570)
274 (3.81) 278 (580) 266 (550)
221 (4.32) 273 (580) 260 (370)

228 (2860) 214 (8000)

 

For example, 52 (30) has kmax 210 mu (8 2640). Thus the

ultraviolet spectrum of a benzocyclobutene such as 52' should

 

 

52

be a good model for that of 42; The ultraviolet spectrum
of the olefinic product from the irradiation of ég'has
maxima at 274 (e 1910), 267 (s 1980) and 211 mu (8 8580)
with shoulders at 262 (s 1470) and 230 mu (8 4860). This
spectrum is nearly identical to that of 54 and hence 48'

is assigned the structure of a 2,3-benzobicyclo[3.2.0]hepta-

2,6-diene.

18
Irradiation of a 1% ether solution of ég'through a
Corex filter with a Hanovia L 450-w lamp afforded a 70%
yield of 2,3-dimethylnaphthalene, EZ/ and an 8% yield of
4,4,6,7-tetramethyl-2,3-benzobicyclo[3.2.0]hepta-2,6-diene,

58; 2,3-Dimethylnaphthalene was identified by comparison

 

 

with an authentic sample. Compound 58 analyzed well for
the formula C15H18. The nmr spectrum of this clear oil
consisted of three-proton singlets at T 8.90 and 8.70,
overlapping quartets at T 8.43 and 8.41 (6H together, J =
1.2 Hz), broad (hw = 4.5 cycles) one-proton singlets at

T 7.13 and 6.31 and a singlet at T 3.04 (4H, aromatic
protons). The ultraviolet spectrum of 58 in 95% ethanol
showed maxima at 273 (e 1560), 266 (g 1450), 260 (s 1020)
and 228 mu (5 2230) with shoulders at 253 (5 620) and

213 mu (6 1920).

The formation of gl'from 52 can be accounted for by
the initial formation of the benzonorcaradiene 62 which
then photochemically rearranges to provide'gl; An analogous
photorearrangement of the type 62'-—> gl'has been observed
by Ciganek in the photoisomerization of 7,7-dicyano-2,3-

benzonorcaradiene, 62” to give 52 (33). Either the

19

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

O
.0
R
hv
I ether
R
:62,
”'—‘ R
\\//
> >
R \
L_ .4
60
NC
CN NC
hv /
00 > I .
\\
62 54

My

photochemical elimination of carbon monoxide from an inter-
mediate cyclobutanone as 63“ or the elimination of carbon
monoxide from the diradical species 64 or 22: followed by
appropriate rebonding, would account for the formation of 62;
The photodecarbonylation of cyclobutanones has ample prece-

dent in the reports of Srinivasan (34), Quinkert (25), and

20

 

0‘ 0 In
R ‘\O
63 64 65

Turro (35).
The conversion of 62 to 61 can also be effected thermal-

ly. For example, 66 (R1 = CH3; R2 = H) at 4500 was converted

o
// R1
R1 R2
R2 / K/
A
| / >
\ - R
R2 2
R
1 1
66 67

w
m

 

to QZ'(R1 = CH3; R2 = H) (17.8%), dimethylketene (17.9%),
and 80% of recovered 66 (23). Thus the thermal elimination
of dimethyl ketene from 22/ a reverse Diels-Alder reaction,
proceeds quantitatively, but requires temperatures (450-
550°) which might be considered unusually high, particularly
when the aromaticity of the product is taken into account.
Thus the ease with which ketenes are formed in the photo-
chemical reverse Diels-Alder reaction §§'-—> 62 stands in
marked contrast to the high temperatures required for the
thermal reaction. If these reactions are considered as
concerted reverse 2 + 4 cycloadditions, then these results

would be contrary to the expectations of the Woodward-Hoffmann

21
rules (36). Since the photochemical reaction of gg'in-
volves excitation of the carbonyl group, it may be neces-
sary to include the carbon—oxygen double bond in the elec-
tron count for predictions concerning cycloadditions involving
ketenes. The further observations that ketenes undergo
thermal 2 + 2 cycloadditions (37) in a presumably concerted
fashion (38) and that ketenes are not reactive as dienophiles
in the DielS<Alder reaction (37) suggest that a more de-
tailed theoretical treatment of all cycloadditions involving

ketenes is required.

C. The Photosensitized Rearrangements of 1,3,3,4,7,8—Hexa—
methyl—5,6—benzobicyclo[2.2.2]octa-5,7-dien-2-one (46)
and 3,3,7,8—Tetramethyl-5,6-benzobicyclo[2.2.2]octa-

5,7-dien—2-one (56)
#—

 

 

As described in Section B, irradiation of an ether solu—
tion of ég'through a Corex filter with a high pressure
mercury arc lamp affords 1,2,3,4-tetramethylnaphthalene, 21x

(82% yield) and 4§'(13%). However, irradiation of 42 with

1;. >*. 6&7/
/et er
0 \ \
/
47

| /

O
22, & 21+ 48 + .‘
acetone ’“V

68

 

 

22
acetone sensitization under identical conditions provides
not only 41'(45% yield) and 48 (6% yield), but also an
isomeric ketonic photoproduct 22/ mp 100—1020, in 26% yield.
From its analysis and spectral properties 68 has been identi—
fied as 1,2,4,4,5,8-hexamethyl—6,7-benzotricyclo[3.3.0.02:8]-
oct—6-en-3—one. The ir spectrum of 68 shows an intense
carbonyl absorption at 1720 cm.1 which is typical of a
.cyclopropane ring conjugated with a highly substituuxlfive-
membered ring ketone (39). The ultraviolet spectrum of 68'
has maxima at 278 (s 1150) and 270 mu (5 1370) with a shoulder
at 263 mu (5 1450) and is indicative of negligible inter—
action between the carbonyl function and the aromatic ring.
The nmr spectrum (CD3CN) of leconsists of three—proton
singlets at T 9.44, 8.90, 8.74, 8.68, 8.63 and 8.57 and an
aromatic multiplet, T 2.90—3.22 (4H), and is consistent
with the assigned structure.

(As discussed in detail in the Introduction, the most
common photochemical transformation of medium-sized mono-
cyclic and bicyclic B,y—unsaturated ketones involves a 1,3-
acyl shift and migration of the allylic double bond. How-
ever, 3-cyclohexenones have only been observed (8,9) to

photochemically rearrange in solution with 1,2-acyl migra-

 

tion to yield conjugated cyclopropyl ketones. Thus irradia-
tion of a tfbutyl alcohol solution of 5 through a Pyrex
filter gives g'in greater than 60% yield (8). The multi-

plicity of this photorearrangement has not been reported.

23

o o»:

O
2' 6

As the formation of benzotricyclic ketone gg'only
occurs with acetone sensitization, the photoisomerization
1§-——> 68 must proceed via the triplet. Two molecular

pathways seem reasonable for the formation of 68 from 42;

/ J<

 

46'

(a) acyl migration in 46 from C-1 to C—7 followed by re-
bonding between C—1 and C-8, analogous to the photorear-
rangement §'——> 6” or (b) a regiospecific (40) di-W-
methane rearrangement (41) in which only one of the two
possible products (fig'or 62) which might be formed gig
benzo-vinyl bridging is observed. A detailed mechanism
for the formation of fig'from 22,212 a di-w-methane rear-
rangement (path b) is presented in Figure 1.

.Differentiation between these two mechanisms is pose

ible by identification of the ketonic photoproduct formed

in the sensitized irradiation of tetramethyl ketone 56, for
acyl migration (path a) would provide ketone 12“ while a

di-iT-methaie rearrangement (path b) would give'u and/or 12.

24

 

\\
68 9 O

m m

Figure 1. A detailed mechanism for the formation of 68'
(or 62) from 46 via a di-w-methane photorear-
rangement.

25

 

O
l/
H
/
\\
H
26
yhv
Path a Path b
#1...) 00
H

70 735 72

m

Acetone sensitized irradiation of 56 through a Corex

filter with a Hanovia L 450-w lamp provides 2,3-dimethyl-

naphthalene (66% yield), 58 (6% yield) and an isomeric

ketonic product, A, in 9% yield. The ir spectrum of this

fl

/ / _Lv__> + / /+
| / acetone I I
\\ \\

57 58

I'W

 

an»

 

 

 

:22?

 

26
clear oil shows a strong carbonyl absorption at 1721 cm-1

and its ultraviolet spectrum has maxima at 279 (s 660) and

271 mu (8 840) with a shoulder at 263 mu (8 930). The nmr

spectrum of A, consists of three-proton singlets at T 9.38,

8 -79, 8.65 and 8.44, sharp one-proton singlets at T 7.80

and 6.97 and an aromatic multiplet, T 2.81-3.10 (4H) .

Reduction of ketone A with lithium aluminum hydride

yields alcohol 13', which has been identified as 1,2,4,4-

tetramethyl-G , 7—benzotricyclo[3 .3 .0 .02 . 8] oct—6-en-anti—3-ol .

 

mun-IVE. «v .

 

—1
A characteristic infrared absorption (28,42) at 3644 cm

defines the stereochemistry of the hydroxyl group as being

anti to the benzene ring. The nmr spectrum of 7,3, consists

0f three-proton singlets at T 9.22, 8.95, 8.80 and 8.57,
3113332 one-proton singlets at T 8.20, 7.30 and 6.92, and

an aromatic multiplet, T 2.90-3.13 (4H). Consequently,

the nmr spectrum of 13 requires a reduction product in

which there are no protons on adjacent carbon atoms.
A.

~

Thus
the precursor of 2,3,, must be ketone 1Q, 1,2,4,4-tetra-

methyl-6 , 7-benzotricyclo[3 .3 .0 .02 ' 8] oct-6-en-3-one . The

identification of A as ketone 22 requires that the photo-

cmemical formation of 15’ from 24' occurs from the triplet

27

 

 

R
hv r . V 0
acetone '
R
74 7.9.
Via 1,2-acyl migration (path a). I‘

Having determined the mechanism for the photorear—

rangement 46 -—> 68: the correct nmr assignments for the

 

 

    

\
/ I/b I” O
acetone
\ B
22

:32.
methyl groups of 2.8.. can be determined by'examination of the

ke tone photoproducts from suitably labeled benzobicyclo-

[2 . 2 .2] octadienones . The labeled benzobicyclo[Z .2 .2] octa-

dienones were prepared as previously described (28) . Ace-

tone sensitized irradiation of 16 provided ketone 71. The

/ / h" ‘ 0., O
\ I acetone
093
22. 11 ”3

nmr spectrum (CD3CN) of uwas identical with that of 6,8"

 

e)‘Ecept for the absence in 21 of the signal at T 8.57

28
present in 68. Similarly, acetone sensitized irradiation

of 18" gave ketone 22’. The nmr spectrum (CCl4) of 12. was

i

D
/ / 3
\ acetone

78

(W

 

essentially identical with that of 68 except for the absence
in 22 of the signal at T 8.74 present in ’68. Thus the nmr
assignments of the signals in 2.8.. are as follows: T 9.44
(3H, a methyl at C-4) , 8.90 (3H, (:3 methyl at C-4) , 8.74
(3H, methyl at C-2) , and 8.57 (3H, methyl at C-5) . The
three-proton singlets at T 8.68 and 8.63 are tentatively

assigned to the methyls at C-1 and C—8, respectively.

D - The Photosensitized Rearrangements of 1 , 3 , 3 , 4 , 7 , 8-Hexa—
methyl—5 , 6—benzobicyclo[2 .2 .2] octa-5 , 7-dien—2 -ols (22

and 91)
A

The photochemical conversion of a divinylmethane moiety
into a vinylcyclopropane group has recently been suggested
by Zimmerman (41) to be a general type of excited-state
transformation. An example of this reaction is the photo-

isomerization of barrelene, 8‘2, to give semibullvalene, Q];

I h V > .70
acetone

80 e2,

 

 

29
(41,43,44). Several recent reports have described the
‘pmotosensitized rearrangement of benzobarrelene, 82 (45,46)
23nd substituted benzobarrelenes (44,47) to provide appro-

Eariately substituted benzosemibullvalenes, 83; Rationaliza-

’/ l hv > “’ I)
\\ acetone V,

:52. es:

 

 

t:j_on of this isomerization by a di—w-methane rearrangement u

:iridicates that two types of bonding are possible as initial

<3)<cited—state processes. Vinyl-vinyl bridging in 82 would

ILeaad.to intermediate 84/ whereas, benzo—vinyl bridging would

ggjgve 82; Zimmerman has investigated this problem in detail

Vinyl- benzo-
<vin 1 vinyl > I’ .
bridging \\ ridging \\

82 :32,

W

iirufl has reported (45) that the photosensitized rearrange-

Ineuit 82’-9 83 proceeds by vinyl-vinyl bridging, not benzo-

‘ViJnyl bridging.

However, di-w-methane rearrangements which do involve

lbeuizo-vinyl bridging have been observed, for example, irradi-

ation of an acetone solution of dibenzobarrelene, 86,

30

affords dibenzosemibullvalene, ’81, in high yield (46,48).

es, §1

S imilarly , the photoisomerization of benzonorbornadiene ,
88 , to tetracyclo[5 .4 .0 .02 . 4 .03 . 6] undeca—l (7) ,8 , 10-triene ,

89. can be readily explained by benzo—vinyl bridging in a

rW ’W

 

d i -Tr-me thane rearrangement .
As discussed in Section C, the photo-sensitized rear-
rangement 46—> 6,8" occurs from the triplet via a 1,2-acy1

migration and not by a di-Tr-methane rearrangment. However,

rw

if the carbonyl chromophore in 46 were replaced by a non—
absorbing substituent, there was ample precedent that the

resulting benzobicyclo[2.2.2]octadiene might photochemically

31
react by a di-T-methane rearrangement.
Reduction of ketone (4’6, with lithium aluminum hydride
gave a 37:63 mixture of the epimeric alcohols ’92 and 91,

which were separated as previously described (28).

if?

 

 

46 9O 91

m m A", '1:i

Irradiation of 1,3,3,4,7,8—hexamethyl-5,6—benzobicyclo-
[2.2.2]octa-5,7—dien—gi_t_;_i_-2-ol, ’92,, with acetone sensitiza-
tion through a Corex filter with a Hanovia L 450-w lamp,
When allowed to proceed to 85% conversion, provided a 73%
yield of a (3:2 mixture of two alcohols, 2.2.. and ’93. Alcohol

92, mp 81-830, has been identified as 1,2,3,3,5,8-hexa-

 

 

methyl-6 , 7-benzotricyclo[3 .3 .0 .02 . 8] oct-6—en—_a_r_i£i_-4-ol .
Alcohol 9’2" shows a sharp absorption in the ir at 3638
cut-1 which defines the stereochemistry of the hydroxyl

group as being gilt; to the benzene ring. In comparison,

anti-5 , 6-benzobicyclo[2 .2 .2] octen-2-ol , 9,4,. shows a strong

32
hand at 3620 cm.1 in the infrared, whereas syn-5,6-benzo—

bicyclo[2.2.2]octen—2-ol, 95, has a strong absorption at

H OH HO
/
\ l
22, 2.5. p.

 

-1
3586 cm (42). The shift in the hydroxyl band of the syn

—.—.-I- ..'..
u
-

alcohol has been attributed to an internal hydrogen bond-

 

ing of the alcohol function with the aromatic ring. Simi- i
lar effects have been reported in the infrared spectra of
the syn-and fli—5,6-benzobicyclo[2 .2.2]octa-5,7-dien-2—ols,
£9. and ’9’]; (28).

The nmr spectrum of 9,2" consists of three-proton sin-
glets at T 9.88, 9.03, 8.95, 8.83, 8.67 and 8.63, a one-
proton singlet at T 6.78 and an aromatic multiplet, T 2.94-
3 - 04 (4H) .

Oxidation of 9,2 with chromium trioxide-pyridine gave a
ketonic product, mp 87-88.5°, isomeric with 46, which has
been identified by its analysis, spectral properties and
reactivity as 1 , 2 , 3 , 3 , 5 , 8-hexamethyl-6 , 7-benzotricyclo—

[3 .3.0.02'3]oct-6-en-4—one, 6,9,. The infrared spectrum of 619

   

33
has an intense carbonyl absorption at 1725 cm_1. The
carbonyl absorptions of a series of related model ketones,

9§'(49), 92'(7) and 9§'(7) are presented below. If the

substituent effects are assumed to be cumulative,

then the

Q
0

 

22. 21. 22.
1744 cm—1 1742 cm‘1 1727 cm-1

:. 1744-2-17 = 1725 cm'1

\ralue of 1725 cm.1 is exactly what would be expected for

tihe carbonyl absorption of such a highly substitubaibicyclo-

[£3.1.0]hexan-3-one as 62; The ultraviolet spectrum of 29

13218 a maximum at 292 mu (5 1290) with shoulders at 313 (é

800), 301 (g 1230) and 247 mu (8 2980) . The enhancement

fo the n ——> n* transition in Qg'is typical of other

‘tNVisted B,y—unsaturated ketones (1,2,17). The nmr spectrum

fo ketone Qg'contains three~proton singlets at T 9.50, 9.00,
8 .80, 8.77, 8.58 and 8.50, and an aromatic multiplet,
T‘ 2.92-3.08 (4H) and is consistent with the assigned struc-
tllre.

Alcohol 23, mp 90-920, also formed in the photoisomeri-
Zation of the 3%; alcohol 92', has been identified as
31,2,4,4,5,8-hexamethyl-6,7-benzotricyclo[3.3.0.02v8]oct-6-

en-anti-3-ol. Alcohol 92 shows a sharp absorption in the

34

infrared at 3642 cm'1 which defines the stereochemistry of

the hydroxyl substituent as being anti to the benzene ring

(42) . The nmr speCtrum of 23' has three—proton singlets at

T 9.33, 9.13, 8.90, 8.85, 8.80 and 8.67, a one-proton

singlet at T 7.08 and an aromatic multiplet, T 2.94—3.20
(4H).

Oxidation of alcohol 23’ with chromium trioxide-pyridine

gave ketone 98. A discussion of the spectral characteris-

tics of 28. appears in Section C. Reduction of £8. with

<——-_—————-—
L1A1H4

   

lithium aluminum hydride provided only the anti-alcohol ’93,.

Thus hydride attack on ketone 28., occurs exclusively syn to

the benzene ring. Apparently hydride attack on ketone 28"

iiriti to the benzene ring is sterically more hindered.
The formation of alcohols gz'and gg'in the acetone
Seansitized irradiation of §2£i_alcohol 22 can readily be
'eliplained by a di-w-methane photorearrangement. As alcohol
22' is unsymmetric with respect to the di-vr-methane moiety,
tfivo different benzo-vinyl bridgings are possible. As can

ENE seen in Figure 2, initial bridging of C-6 and C-7 (path

21) provides alcohol 93/ whereas bridging C-5 and C-8 (path
13) gives 9’2".

35

 

 

22.
hv
rOH Path a Path b H 0H
J w / Q C
\
H OH

O" T
i

on

22, 92

W

 

Figure 2. A detailed mechanism for the formation of 22' and
92 from 92’ via a di-vr-methane photorearrangement.

36

However, in marked contrast with the anti-alcohol 22,
identical irradiation of 1,3,3,4,7,8-hexamethyl-5,6—benzo-
bicyclo[2.2.2]octa-5,7-dien-§y272—ol, 91, provided only a
single alcohol, 92; Irradiation to only 18% conversion of
gl'gave a 97% yield of 92/ whereas at 80% conversion, the
yield of 92 was 68%. Alcohol 92/ mp 72-730, has been
identified as 1,2,3,3,5,8—hexamethyl-6,7-benzotricyclo—

[3.3.0.02'3]oct-6-en-syn-4—ol. The infrared spectrum of 92'
H OH

I’
l I __JDL___>
\\ acetone

 

has a sharp absorption at 3580 cm”1 which determines the
stereochemistry of the hydroxyl group as being syn to the
benzene ring (42). The nmr spectrum of 92 consists of
three—proton singlets at T 10.00, 9.02, 8.93, 8.83, 8.67
and 8.62, a broad one—proton signal, T 6.53-6.73, and
an aromatic multiplet, T 2.88—3.13 (4H).

Oxidation of alcohol 92 with chromium trioxide—

pyridine gave ketone 62, while reduction of 62 with lithium

aluminum hydride provided only the syn-alcohol 92; Therefore

 

 

Cr03,Pyr.‘ 0 V
<LiAlH4
o

69

W

 

I 'm‘

 

37
hydride attack on ketone 62 occurs exclusively a§£i_to the
benzene ring.

As alcohol gl'is unsymmetric with respect to its di-W-
methane moiety, two different benzo-vinyl bridgings are
possible. As shown in Figure 3, initial bridging of C-5
and C-8 (path a) would provide 22/ whereas bridging C-6 and
C—7 would give 122; However, acetone—sensitized irradiation
of the gygfalcohol 91 affords only a single product, 92;

No lQPVfiB formed. The regiospecificity (40) in this re-
arrangement indicates a strong preference for intermediate

101 vis-a-vis 102. No such preference is observed in the

o H
H/ %r

 

 

 
    
 

ob- not
servedégg’ lggfobserved'o

\

 

photorearrangement of the anti-alcohol 92; Possible factors
which may contribute to the preference of 121 over 122 may
be: (1) internal hydrogen bonding between the alcohol sub—
stituent and the w-electron system of the benzene ring, or
(2) a charge—transfer interaction between the oxygen atom
of the alcohol function and the w—electron system of the

fused aromatic ring.

91

NV

hv
Path a Path b HO H
/
O
H

 

i

H HO
I
/l ./ /|
\\ ‘- ‘\

 

100

I'M

 

Figure 3. A detailed mechanism for the formation of 92'
(or 100) from 91 via a di—w-methane photorear-
rangement.

EXPERIMENTAL
A. General Procedures

All ultraviolet spectra were measured with a Unicam
Model SP-800 spectrophotometer. The infrared spectra were
obtained on a Unicam Model SP—200 infrared spectrometer or
a Perkin—Elmer Model 2373 grating infrared spectrophotometer
and all ir spectra were calibrated (polystyrene). The nmr
spectra were measured with a Varian A—60 or a J.E.O.L.

C—60H spectrometer using tetramethylsilane as an internal
reference. The mass spectra were carried out by Mr. M.
Petschel of this laboratory with a Consolidated Electro-
dynamic Corp. 21-103C instrument operating at an ionizing
potential of 70v. Melting points were obtained with an
Electrothermal melting point apparatus and are uncorrected;.
.Elemental analyses are by Spang Microanalytical Laboratories,
Ann Arbor, Michigan or Clark Microanalytical Laboratory,

Urbana, Illinois.
B. General Photolysis Procedures

All irradiations were conducted with a 450-watt Hanovia
Type L mercury lamp with the light filtered through a Corex
glass sleeve. The solution to be irradiated was placed in
a quartz test tube, sealed with a serum cap and attached to

39

40
the outside of a Hanovia quartz immersion well, 2—3 cm from
the center of the mercury arc. This apparatus was then
placed in a water bath, which maintained the temperature
of the solution during irradiation between 15 and 20°.

The photolyses were monitored by withdrawal of small
aliquots at various time intervals and examination of these
by vapor phase chromatography (vpc). After the irradiations
were completed, the solvent was removed at reduced pressure
and a suitable internal standard was added to the crude
reaction mixture. Analysis by vpc (using appropriate cali-
bration curves) and/or nmr integration provided the reported
yields. The Vpc calibration curves were obtained by anal—
ysis of carefully prepared standard solutions of the react-
ants, products and standard. The specific method employed
to determine the yield is noted in each experiment.

For each successful irradiation experiment reported, a
control reaction was carried out in which a solution identi-
cal to that irradiated was prepared, sealed with a serum
cap in a quartz test tube and stored in the dark. After
two weeks the solvent was evaporated and ir and nmr
spectra of the residue were obtained. Spectra identical
to those of the starting material resulted in all cases.

No "dark" reactions were detected in vpc analysis of the

residues.

41

C. Irradiation of 1,3,3,4,7,8—Hexamethy1-5,6—dicarbometh—
oxybicyclo[2.2.2]octa—5,7—dien—2-one egg) in Diethyl
Ether

 

A solution of 102 mg of 32'(22) in 10 ml of diethyl
ether was irradiated through a Corex filter with a 450awatt
Hanovia Type L mercury lamp. Monitoring the photolysis by
Vpc (10' x 1/4" SE-30 column; 220°; 50 ml/min of He) indi—
cated the formation of a single photoproduct. The photo—
product was purified by vpc (above conditions) and was shown
to be identical in all respects (mp: 126-127°; nmr spec-
trum (CC14): sharp singlets at T 7.82 (12H) and 6.28 (6H);
ir spectrum; Rt) with an authentic sample of dimethyl
3,4,5,6-tetramethylphthalate (31) previously prepared in
this laboratory (22).) Irradiation of an identical solution
under the above conditions for two hours provided an 80%

yield (Vpc, pfdibromobenzene as standard) of 31;

D. Irradiation of 1L3,3,4,7,8-Hexamethyl-5,6-diphenylbi-
cyclo[2.2.2]octa-5,7-dien—2—one (32) in Diethyl Ether

 

A solution of 130 mg of 32 (22) in 10 ml of diethyl
ether was irradiated through a Corex filter with a 450—watt
Hanovia Type L mercury lamp. Monitoring the photolysis by
vpc (5' x 1/8" SE-30 column, 280°, 90 ml/min of He) indi-
cated the formation of a single photoproduct. Monitoring
the photolysis by uv revealed a sharp decrease in the

shoulder absorption of gg'at 300-310 mu. The uv spectrum

remained constant after three hours irradiation. The

42

photoproduct was purified by chromatography on silica gel
(pentane eluant) and was shown to be identical in all re-
spects (mp: 125—1270; nmr spectrum (CCl4): six—proton sing-
lets at T 8.04 and 7.73 and a broad aromatic multiplet, T
3.03—3.23 (10H); ir Spectrum) with an authentic sample of
3,4,5,6-tetramethyl—1,2-diphenylbenzene (32) previously pre—
pared in this laboratory (22). Irradiation of an identical
solution under the above conditions for three hours pro-
vided an 83% yield (vpc, hexamethylbenzene as standard;
nmr, methylene bromide as standard) of £2.

Similarly, a solution of 101 mg (2.8 x 10”4 mole) of
32 in 10 ml of diethyl ether was sealed in a quartz test
tube and irradiated through a Corex filter with a 450-watt
Hanovia Type L mercury lamp for four hours. Upon completion
of the irradiation, the solution was treated with 48 mg

(5.6 x 10'4

mole) of aniline. After evaporation of the sol-
vent, the photosylate residue was chromatographed on silica
gel. Elution with pentane provided 65 mg of 33” and further
elution with methylene chloride—ethanol (1:1) gave 35 mg of
a solid, mp 100-1020. This material proved to be identical

(mixed mp and ir Spectrum) with an authentic sample of

isobutyranilide (32).

43

E. A Low Temperature Study of the Photolysis of 1,3,3,4,7,8-
Hexamethyl-S,6-diphenylbicyclo[2.2.210cta-5,7-dien—2-one
(22)

The apparatus used in this experiment was designed by
Dr. Johnchiffiths of this laboratory. This apparatus con-
Sisted of a lead block (designed to hold liquid nitrogen)
into which a sodium chloride cavity cell (0.2 mm pathlength)
could be set gig a hole suitably drilled in the block. The
metal block was insulated by a close fitting styrofoam box.
When the reservoir was filled with liquid nitrogen, the
cell was cooled to an equilibrium temperature of ~100° i
10°C. Suitable aperatures were placed in the metal block
and the styrofoam box which permitUai ir measurements and
irradiation of the cell to be made. Icing of the cavity
cell windows was minimized by passing a vigorous stream of
very dry nitrogen over the cell windows throughout the
experiment.

A solution of 20 mg of 32 in one ml of 2—methyltetra-
hydrofuran was sealed in the cavity cell inside the styro-
foam block and cooled to -100° with liquid nitrogen. The
ir Spectrum of the solution was then recorded, using a
similar pathlength cell containing 2-methyltetrahydrofuran
as reference. The ir Spectrum Showed the strong carbonyl
absorption of gz'at 1705 cm_1. A parallel beam of radiation
from an enclosed 450-watt Hanovia Type L mercury lamp was
filtered through Corex and diverted into the cavity cell.

Examination of the ir Spectrum after irradiation for five

44

minutes indicated a decrease in the intensity of the ab—
sorption at 1705 cm.1 and the appearance of a Sharp intense
absorption at 2135 cm—1, which is attributed to the forma—
tion of dimethyl ketene, 32; Examination of the ir Spec-
tra after total irradiation periods of 10 min, 25 min, 40
min, and 60 min Showed a progressive decrease in the ab-
sorption at 1705 cm-1 and an increase in the intensity of
the absorption at 2135 cm-1. When the solution was warmed
to room temperature, the dimethyl ketene absorption band

at 2135 cm—1 gradually disappeared.

F. Photolysis of 1,3,3,4,7,8-Hexamethyl—5,6-benzobicyclo—
[2.2.2]octa—5,7-dien-2-one (42) in Diethyl Ether

 

 

A solution of 100 mg of 46 (23,28) in 10 ml of diethyl
ether was irradiated through a Corex filter with a 450-watt
Hanovia Type L mercury lamp. Monitoring the photolysis by
vpc (10' x 1/4" SE-30 column; 220°; 50 ml/min of He) in-
dicated the formation of two photoproducts. The photopro-
ducts were purified by vpc (above conditions). The com-
pound with longer Rt was shown to be identical in all
respects (mp: 105—107°; nmr Spectrum (CC14): six-proton
singlets at T 7.62 and 7.43 and aromatic multiplets cen—
tered at 1 2.72 (2H) and 1 2.10 (2H); ir spectrum) with an
authentic sample (prepared by a modification (50) of the
method of Hewett (51)) of 1,2,3,4-tetramethylnaphthalene,
42; The compound with the shorter R has been identified

t
as 1,4,4,5,6,7-hexamethyl—2,3-benzobicyclo[3.2.thepta—2,6-

 

diene, 48; The mass Spectrum of this colorless oil Showed

45

a parent peak at m/e 226. The ultraviolet spectrum of 48'
in 95% ethanol had maxima at 274 (5 1910), 267 (g 1980),
and 211 mu @:8580) with Shoulders at 262 @ 1470) and 230 mu
(8 4860). The nmr spectrum (CCl4) of 4§'(Figure 4) con—
sisted of singlets at r 8.95 (3H), 8.83 (3H) and 8.75 (6H),
quartets at T 8.53 and 8.50 (3H each, J = 1.2 Hz), and a
Singlet at T 3.05 (4H, aromatic protons).

Aggl, Calcd. for C17H22: C, 90.20; H, 9.80

Found: C, 90.25; H, 9.72.

When an identical solution of 42 in diethyl ether was
irradiated under the above conditions for six hours, the
reaction proceeded with 86% conversion (vpc, pfdibromo-
benzene as standard) of ég'to give an 82% yield of 1,2,3,4—

tetramethylnaphthalene and a 13% yield of 48;

G. Photolysis of 4-Methylfg3-1,3,3,7,8-pentamethyl-5,6-
benzobicyclo[2.2.2]octa-5,7-dien-2-one (193) in
Diethyl Ether

Irradiation of a solution of 150 mg of 123 (28) in 11
ml of diethyl ether through a Corex filter with a 450-watt
Hanovia Type L mercury lamp for eight hours provided a mix-
ture of two photoproducts which were separated by vpc
(10' x 1/4" SE-30 column; 220°; 50 ml/min of He). The nmr
spectrum (CCl4) of the compound with the shorter Rt con-
sisted of singlets at T 8.96 (3H) and 8.76 (6H). a multi-
‘plet at T 8.53-8.50 (6H) and a Singlet at T 3.03 (4H,

(aromatic protons). Thus the nmr Spectrum of this

46

 

. 3.3 283-6 . m
Imummnmo.m.mHoHomoHQoucmnlm.mlawsumamxmglb.m.m.v.v.fl mo Aaauuv ennuommm HEZ

P .3 T Q
q _

—L~

S
m
n-

.v musmflm

 

 

~01

 

 

 

m---

 

 

 

 

 

A ’.--_ ..___

 

 

 

 

 

.—

 

47
photoproduct is essentially identical with that of un— '
labeled 48 except for the absence here of the peak at

T 8.83 in'ggx

H. Photolysis of 7-Methyl-d3-1,3,3,4,8-pentamethyl—5,6-
benzobicyclo[2.2.2]octa-5,7-dien-2-one (104) in
Diethyl Ether

Irradiation of a solution of 124 mg of 122'(28) in
10 ml of diethyl ether through a Corex filter With a 450-
watt Hanovia Type L mercury lamp for eight hours gave a
mixture of two photoproducts which were separated by vpc
(10- x 1/4" 53-30 column; 220°; 50 ml/min of He). The nmr
Spectrum (CC14) of the compound with the Shorter Rt con-
sisted of singlets at T 8.94 (3H), 8.84 (3H), 8.72 (6H),
8.50 (3H) and 3.06 (4H). Examination of the nmr spectrum
at a sweep width of 50 cycles confirmed the Signal at T 8.50
to be a singlet. Thus the quartets at T 8.53 and 8.50
(3H each, J = 1.2 Hz) of unlabeled 48 have been replaced

here with a singlet at T 8.50.

I. Irradiation of 3,3,7,8—Tetramethyl-5,6-benzobicyclo—
[2.2.2]octa-5,7—dien-2-one (§§)in Diethyl Ether

A solution of 100 mg of 52'(22) in 10 ml of diethyl
ether was irradiated through a Corex filter with a 450-watt
IHanovia Type L mercury lamp. Monitoring the photolysis by
‘vpc (10' x 1/4" 52-30 column; 220°; 60 ml/min of He) indi-

cated the formation of two photoproducts. The photoproducts

48

were purified by Vpc (above conditions). The compound,
with longer Rt was shown to be identical in all reSpects
(mp: 105-108°; mixed mp; ir and nmr Spectra) with an
authentic sample (Aldrich Chemical Co., recrystallized
twice from ethanol) of 2,3—dimethylnaphthalene, 51; The
compound with the shorter Rt has been identified as
4,4,6,7-tetramethyl-2,3-benzobicyclo[3.2.thepta-2,6-diene,
58; The ultraviolet Spectrum of this clear oil in 95%
ethanol Showed maxima at 273 (5 1560), 266 (e 1450), 260
(5 1020) and 228 mu (5 2230)with shoulders at 253 (g 620)
and 213 mu (5 1920). The nmr spectrum (CCl4) of fig
(Figure 5) consisted of three-proton singlets at T 8.90
and 8.70, overlapping quartets at T 8.43 and 8.41 (6H
together, J = 1.2 Hz), broad (hw = 4.5 cycles) one-proton
singlets at T 7.13 and 6.31 and a singlet at T 3.04 (4H,
aromatic protons).

Anal. Calcd. for C15H18: C, 90.85; H, 9.15

Found: C, 90.77; H, 9.21.

When a solution of 70 mg of 56 in 7 ml of diethyl
ether was irradiated under the above conditions for four
hours, the reaction gave a 70% yield (vpc, pfdibromobenzene

as standard; nmr, methylene bromide as standard) of 2,3-

dimethylnaphthalene and an 8% yield of 58”

 

49

HQ

 

. Awmv memeesmd
Imummnno.N.mgoaowuflnoucmnum.NlamaumamuumUIh.®.v.v mo AwHUUV Ennuommm H82 .0 musmflm

 

 

“I...

 

“oh-u-e——

 

 

 

 

m N
4

10¢}:

 

 

50

J. Irradiation of 1,3,3,4,7,8—Hexamethyl-546—benzobicyclo-
[2.2.2]octa-5,7-dien-2-one (42) in Acetone

 

A solution of 110 mg of 42 (23,28) in 10 ml of acetone
was irradiated through a Corex filter with a 450—watt Hanovia
Type L mercury lamp. Monitoring the photolysis by vpc
(10' x 1/4" 53-30 column; 220°; 50 ml/min of He) indicated
the formation of three photoproducts. The photoproducts
were purified by vpc (above conditions). The main product
(intermediate Rt) was Shown to be identical in all respects
(mp, ir and nmr Spectra, Rt) with an authentic sample (pre-
pared by a modification (50) of the method of Hewett (51))
of 1,2,3,4-tetramethylnaphthalene, 41; The compound with
the shortest Rt was identified (Rt, ir and nmr Spectra)
as 1,4,4,5,6,7—hexamethyl-2,3-benzobicyclo[3.2.0]hepta¥2,6-
diene, 4§'(See Section F for Spectral characteristics and
analysis). The compound with the longest Rt has been
identified as 1,2,4,4,5,8-hexamethyl—6,7—benzotricyclo—
[3.3.0.02:810ct-6-en-3-one, 68; This white solid, mp 100-
102°, showed an intense absorption in the ir (CCl4) at

1720 cm"1 ) and its ultraviolet spectrum (95% ethanol)

(Vc-o
had maxima at 278 (s 1150) and 270 mu (8 1370) with a
shoulder at 263 mu (8 1450). The nmr Spectrum of gg'in CCl4
(Figure 6) consisted of three-proton singlets at T 9.44,
8.94, 8.74 and 8.69, a Six-proton Singlet at T 8.60 and an
alxxnatic multiplet, T 2.85-3.14 (4H); while the nmr spectrum
(sf Qg'in CD3CN showed three-proton singlets at T 9.44, 8.90,

£3.74, 8.68, 8.63 and 8.57 and an aromatic multiplet, T 2.90-

.3.22 (4H).

51

.dmmv mCOIMIcmlm
IpUOHm.No.0.m.mHoHomoHHuoucwnlh.mlawzumfimxmnlm.m.w.w.N.H mo Avaoov Esuuommm HEZ .m onsmfim

a r 4 v m u
4 a

 

‘U

—=

 

 

52

Anal. Calcd. for C13H220: C, 84.99; H, 8.72

Found : C, 84.65; H, 8.54.

Irradiation of a solution of 101 mg of 4,6, in 10 ml of
acetone under the above conditions for nine hours proceeded
with 91% conversion of 4,6, and gave a 45% yield (vpc, E‘
dibromobenzene as standard; nmr, methylene bromide as stand-

ard) of 1,2,3,4-tetramethylnaphthalene, a 6% yield of 42' ,

and a 26% yield of the ketonic product 68'.

Irradiation of 4-Methyl-c_1_3 -1 , 3 , 3 , 7 ,8-pentamethyl-5 , 6-

K.
benzobicyclo[Z .2 .2] octa-5 , 7-dien-2-one (76) in Acetone
m

Irradiation of a solution of 105 mg of 2,6. (28) in 10
ml of acetone through a Corex filter with a 450-watt Hanovia
Type L mercury lamp for 9.5 hours afforded a mixture of

three photoproducts which were separated by vpc (10' x 1/4“

SE-3O column; 220°; 50 ml/min of He). The nmr spectrum

(CC14) of the compound with the longest Rt (the ketonic

photoproduct) Showed singlets at T 9.44 (3H) , 8.95 (3H) ,

8.75 (3H), 8.70 (3H) and 8.60 (3H) and a multiplet T 2.86-

3.15 (4H, aromatic protons). Comparison of this nmr spec-

trum with that of unlabeled 28’ shows that the six-proton
singlet at T 8.60 ingg now integrates for only three pro-

tons . The nmr spectrum of this labeled ketonic photoproduct

n CD3CN consisted of three—proton singlets at T 9.44, 8.90,

.74, 8-.68 and 8.62 and an aromatic multiplet, T 2.75-3.06

4H) . Thus this nmr spectrum of the labeled ketonic photo-

roduct differs from that of unlabeled 2.8. (in CD3CN) in the

bsence here of the peak at T 8.57 in 6,8,;

 

53

L. Irradiation of 7-Methyl—d3 -1 , 3 , 3 , 4 , 8-pentamethyl-5 , 6-

benzobicyclo[2 .2 .2] octa-5 , 7-dien-2-one (18‘) in Acetone

 

 

 

Photolysis of a solution of 100 mg of '78 (28)in 12 ml
of acetone through a Corex filter with a 450-watt Hanovia
Type L mercury lamp for nine hours provided a mixture of

three photoproducts which were separated by Vpc (10' x 1/4"

 

SE-30 column; 220°; 50 ml/min of He). The nmr spectrum

(CCl4) of the compound with the longest R (the ketonic

t
photoproduct) has singlets at T 9.44 (3H), 8.95 (3H), 8.70

 

(3H), 8.60 (6H) and a multiplet T 2.88-3.20 (4H, aromatic 15)
protons). Thus the three-proton singlet at 'r 8.75 present

in the nmr Spectrum of unlabeled 9.8.. is absent here.

M. Irradiation of 3 , 3 , 7 , 8-Tetramethyl-5 , 6-benzobicyclo-
[2 .2 .2] octa-5 , 7-dien-2-one (56) in Acetone

 

A solution of 120 mg of 5,6, (22) in 10 ml of acetone
was irradiated through a Corexfilter with a 450-watt
Hanovia Type L mercury lamp. Monitoring the photolysis by
vpc (10' x 1/4" SE-30 column; 220°; 60 ml/‘min of He) in-

dicated the formation of three photoproducts. The photo-
products were separated and purified by vpc (above condi-
tions) . cThe main product (intermediate Rt) was shown to
»e identical in all respects (mp, ir and nmr spectra, Rt)
ith an authentic sample (Aldrich Chemical Co., recrystal-
ized twice from ethanol) of 2,3-dimethylnaphthalene, 52'.
he compound with the Shortest R 'ir

was identified (R

t t'

 

54

spectnmn as 4,4,6,7-tetramethyl-2,3-benzobicyclo[3.2.0]-
hepta-2,6-diene, 58' (see Section I for spectral character-

istics and analySiS) . The compound with the longest Rt

has been identified as 1,2,4L4-tetramethyl-6,7-benzotri-
cyclo[3.3.0.02'8]oct-6-en-3-one, 22, The ir Spectrum
(CC14) of this clear oil showed a Strong absorption at

1 (

1721 cm_ vC-o) and its ultraviolet spectrum (95% ethanol)

had maxima at 279 (5 660) and 271 mu (6 840) with a shoulder
at 263 mu (8 930). The nmr spectrum of 12 in CCl4 (Figure
7) consisted of three-proton singlets at T 9.38, 8.79, 8.65
and 8.44, sharp one-proton singlets at T 7.80 and 6.97 and

an aromatic multiplet, T 2.81-3.10 (4H).

Anal. Calcd. for C16H180: C, 84.91; H, 8.02

Found: C, 84.76; H, 8.05.

Irradiation of a solution of 71 mg of 26 in 7 ml of

acetone under the above conditions for four hours proceeded
with 96% conversion of 56 and gave a 66% yield (nmr,
methylene bromide as standard) of 2,3-dimethylnaphthalene,

a 6% yield of 58/ and a 9% yield of the ketonic product 12;

Reduction of 1,2,4,4-Tetramethyl-6,7-benzotricyclo-
[3.3.0.02'8]oct-6-en-3-one (2g2 with Lithium Aluminum

Hydride

N.

.A solution of 52 mg of ZQ'in 10 ml of dry tetrahydro-

furan was added during 15 min to a suspension of 364 mg of

litldnnn aluminum hydride in 20 ml of dry, vigorously stirred,

refluxing tetrahydrofuran. The mixture was stirred at

In: I.

 

 

 

55

 

Iuoonw.No.0.m.MHOHUwoflHuoucmnlb.olamnpoEmuumUIv.v.N.H mo Avauov Esnuommm H82 .5 onsoflm

 

 

 

wt?

 

 

 

 

Maud}..- .

 

 

 

 

«CD

«V!

.Ava maonmnamlo

 

56
reflux for an additional three hours, then cooled in an
ice bath, and small pieces of ice were added to hydrolyze
the excess lithium aluminum hydride. To this mixture was
added 8 ml of water. The resulting mixture was extracted
with ether (3 x 20 ml) and the separated ether layer was
dried over anhydrous magnesium sulfate. Evaporation of
the ether solution provided an oil which when examined by
vpc (10' x 1/4" FFAP column; 210°; 60 ml/min of He) showed
a Single reduction product. This compound was purified by
vpc (above conditions) and has been identified as 1,2,4,4-
tetramethyl—6,7-benzotricyclo[3.3.0.02'3]oct-6-en-anti-3-ol,
(13). The ir Spectrum (CCl4) of this clear oil showed a
Sharp absorption at 3644 cm-1 (VO_H). The nmr spectrum of
Zé'in CC14 (Figure 8) had three-proton singlets at 1 9.22,
8.95, 8.80 and 8.57, Sharp one-proton singlets at T 8.20,
7.30 and 6.92 and an aromatic multiplet, 1 2.90-3.13 (4H).

Anal. Calcd. for C16H200: C, 84.16; H, 8.83
Found: C, 83.94; H, 8.90.

O. Irradiation of 1,3,3,4,7,8-Hexamethyl-5,6-benzobigyclo-

[2.2.2]octa-5,7-dien-anti-2-ol (92) in Acetone

A solution of 80 mg of 92'(28) in 8 ml of acetone was
irradiated through a Corex filter with a 450-watt Hanovia

Type L mercury kmp. Monitoring the photolysis by vpc (10' x

1/4" FEAP column; 220°; 100 ml/min of He) indicated the forma-
tion of two photoproducts. The photoproducts were separated

and purified by vpc (above conditions). The compound with

57

. AWHMV HOIMI. Hucwlcwlmluuo

 

Hw.N0.0.m.m_ H l I as V H .n
I O 0%0 H. HUONCTQ. . \nnquMHu0UI ‘ e . 0 v
N. D H N H m A 00v ESHUUmnmm HEZ . w GHS@ . .m

or.

 

 

.

 

0: .r

 

 

 

 

 

 

 

58
the shorter Rt has been identified as 1,2,3,3,5,8-hexa-
methyl-6,7-benzotricyclo[3.3.0.02r°]oct-6-en-§gti-4-ol, 92;
This white solid, mp 81-83°, Showed a sharp absorption in'
the ir (CCl4) at 3638 cm_1 (vO_H). The nmr spectrum of 22'
in CCl4 (Figure 9) consisted of three-proton singlets at"
T 9.88, 9.03, 8.95, 8.83, 8.67 and 8.63, a one—proton singlet

at T 6.78 and an aromatic multiplet, T 2.94-3.04 (4H). E!

 

Anal. Calcd. for C18H24O: C, 84.32; H, 9.44.
Found: C, 84.16; H, 9.33.

 

The compound with the longer Rt has been identified :I)
as 1,2,4,4,5,8-hexamethyl-6,7-benzotricyclo[3.3.0.02valoct- g I
6-en-anti-3-ol, 93; This white solid, mp 90-92°, showed a
sharp absorption in the infrared (CC14) at 3642 cm-1. The
nmr spectrum of gg'in CCl4 (Figure 10) had three-proton
singlets at T 9.33, 9.13, 8.90, 8.85, 8.80 and 8.67, a one-
proton Singlet at T 7.08 and an aromatic multiplet, T 2.94-
3.20 (4H).

Anal. Calcd. for C18H24O: C, 84.32; H, 9.44
Found: C, 84.08; H, 9.26.

When a solution of 70 mg of 92 in 10 ml of acetone was
irradiated under the above conditions for two hours, the

reaction proceeded with 85% conversion (nmr, hexamethylbenzene

as standard) of 22 and gave a 44% yield of 92 and a 29%

yield of 93;

 

59

 

I H141... ..-.....
.w . a). ti)... .

 

 

. AME Houvuflcmncouonuoo
nHo.mo.o.m.msoaomoenoouconus.ouemaooemxonlw.m.m.m.m.H mo Aeaoov ssuuoomm usz

“Os ¢ 0 r
4

.m wudoflm

 

 

-‘
q

2 :4

 

 

 

 

 

 

 

 

 

Wig.

 

 

-

 

 

60

 

 

.Amwv HonmlHHGMIsolouuoo
IHm.no.o.m.maoaomofluooucmnlb.olamnuofimxmnlw.m.v.v.N.H mo Aeaouv Esuuowmm HEZ

.oH ousoflm

 

 

 

 

 

 

PO. r m t J m V «- N
. 4 1 e 7 A q 4 L
D
a _
. _
M r ._ _
M _ u H l
_ _ _ a
. l l. l
_ _ _
. lg; _
l :_
W g: i
__ ,_ . .
l l. _
. . H
W Z _
q 1H...
. f
i
l
_

 

_

 

 

 

 

61

P. Oxidation of 1,2,3,345,8-Hexamethyl-6,7-benzotrigyclo-
[3.3.0.0213]oct-6-en—§nti-4—ol (92) with Chromium Tri—

oxide-Pyridine

A solution of 30 mg of gz'in pyridine (1.0 ml) was
added to the ice-cooled complex (52) prepared from chromium
trioxide (385 mg) and pyridine (1.5 ml) and the mixture was
left at room temperature for 46 hrs. Methanol (0.8 ml) and
water (3.0 ml) were then added to the mixture and the re-
sult was extracted with ether (3 x 15 ml). The organic
layer was dried over anhydrous magnesium sulfate and then
evaporated to provide 30 mg of a white solid. This residue
was purified by vpc (10' x 1/4‘" FFAP column; 220°; 100 ml/min
of He) and afforded a single white solid which was identi-
fied (mp, mixed mp, ir spectrum, Rt) as 1,2,3,3,5,8-hexa-
methyl-6,7-benzotricyclo[3.3.0.02'8]oct-6-en—4-one, 62'(see'

Section T for spectral characteristics and analysis).~

Q. Oxidation of 1,2,4,4,5,8-Hexamethyl-6,7-benzotricyclo-
[3.3.0.02I8]oct—6-en-anti-3-ol (223 with Chromium Tri-

 

 

oxide-Pyridine

A solution of 19 mg of gg'in pyridine (1.0 ml) was
added to the ice-cooled complex (52) prepared from chromium
trioxide (385 mg) and pyridine (1.5 ml) and the mixture was
left at room temperature for 41 hrs. Methanol (0.8 ml) and
‘water (3.0 ml) were then added to the mixture and the re-
sult was extracted with ether (3 x 15 ml). ‘The organic

layer was dried over anhydrous magnesium sulfate and then

 

 

62
evaporated to provide 18 mg of an off—white solid which was
identified (mp, mixed mp, ir Spectrum, Rt) as 1,2,4,4,5,8-
hexamethyl-G , 7-benzotricyclo[3 .3 .0 .02 , 8] oct-6-en-3-one , 6'8»

(see Section J for spectral characteristics and analysis).

R . Reduction of 1 , 2 , 4 , 4 , 5 , 8-Hexamethyi-6 , 7-benzotricyclo-

[3 .3 .0 .02 I 8] oct-6-en—3-one (2%) with Lithium Aluminum
Hydride

 

A solution of 150 mg of 6,8, in 10 ml of dry tetrahydro-

furan was added in 10 min to a suspension of 600 mg of

lithium aluminum hydride in 15 ml of dry, vigorously stir-

red, refluxing tetrahydrofuran.

The mixture was stirred
at reflux for an additional 15 hrs, then cooled in an ice

bath, and small pieces of ice were added to hydrolyze the

excess lithium aluminum hydride.

To this mixture was
added 8 ml of water.

The resulting mixture was extracted
with ether (3 x 20 ml) and the separated ether layer was

dried over anhydrous magnesium sulfate. Evaporation of the

ether solution provided a solid which when examined by vpc

(10'): 1/4" FFAP column; 220°; 100 ml/min of He) showed a

single reduction product. This compound was purified by

vpc (above conditions) and has been identified (mp, mixed

mp, ir and nmr spectra) as 1,2,4,4,5,8-hexamethyl-6,7-benzo-
tricyclo[3.3.0.0213]oct-6-en-anti-3-ol, 92 (see Section 0

for spectral characteristics and analysiS) .

 

 

 

63

S. Irradiation of 1,3,3,4,7,8-Hexamethyl-5,6-benzobicyclo-
[2.2.2]octa-5,7-dien-syn-2-ol (91) in Acetone

A solution of 120 mg of 21'(28) in 10 ml of acetone
was irradiated through a Corex filter with a 450-watt
Hanovia Type L mercury lamp. lMonitoring the photolysis by
vpc (10' x 1/4" FFAP column; 220°; 100 ml/min of He) indi—
cated the formation of a single photoproduct. This compound
was purified by vpc (above conditions) and has been identi-
fied as 1,2,3,3,5,8-hexamethyl-6,7-benzotricyclo[3.3.0.02r3]-

oct-6-en-syn-4-ol, 92; This white solid, mp 72-73°, showed

 

a sharp absorption in the infrared (CCl4) at 3580 cm—1

(Vo -H
three-proton singlets at T 10.00, 9.02, 8.93, 8.83, 8.67

). The nmr spectrum of gg'in CC14 (Figure 11) had

and 8.62, a broad one-proton signal at T 6.53-6.73 and an
aromatic multiplet, T 2.88-3.13 (4H).

Anal. Calcd. for C18H24O: C, 84.32; H, 9.44

‘ Found: C, 84.33; H, 9.27.

When a solution of 67 mg of 91 in 7 ml of acetone was
irradiated under the same conditions for ten min, the reac-
tion proceeded with 18% conversion (nmr, hexamethylbenzene
as standard) of 21 and gave a 97% yield of 92; When a solu-
tion of 70 mg of 21;in 10 ml of acetone was irradiated under
the same conditions for 45 min, the reaction proceeded with
80% conversion (vpc, hexamethylbenzene as standard; nmr,
hexamethylbenzene as standard) of gl'and gave a 68% yield

of 22,

 

 

 

64

 

 

. . Ammo Houvucwnucouonooo H... «o. o. m. E
IoHomoHquNchIh.onamsumemxmnlw.n.m.m.N.fi mo Amza o: .vHUUV Eduuommm HEZ

.fiH musoflm

 

 

Po. .- o r o a f n N
a - _ q H a . a _
F
,

e l m.
l .: i l {m
_l 4‘1
_._ a l _
, _._. M__
. l? n..

l.

 

65

Oxidation of 1 , 2 , 3 , 3 , 5 , 8-Hexamethyl-6 , 7-benzotricyclo-

[3 .3 .0 .02 I8] oct-6-en-syn-4-ol (99) with Chromium Tri-
fi m
oxide—Pyridine

 

A solution of 71 mg of 29' in 2.0 ml of pyridine was

added to the ice-cooled complex (52) prepared from chromium
trioxide (770 mg) and pyridine (3.0 ml) and the mixture was
left at room temperature for 48 hrs. Methanol (1.6 m1) and
water

(6.0 ml) were then added to the mixture and the re-

sult was extracted with ether (3 x 15 ml). The organic

layer was dried over anhydrous magnesium sulfate and then

evaporated to provide an off-white solid which when examined
by vpc (10' x 1/4". FFAP column; 220°; 100 ml/min of He) in-

dicated the presence of a single product. This compound
was purified by vpc (above conditions) and has been identi-

fied as 1,2,3,3,5,8-hexamethyl-6,7-benzotricyclo[3.3.0.02:81-
oct-6-en-4-one, 69. This white solid, mp 87-88.5°, showed

. . . . -1
an intense absorption in the 1r (CC14) at 1725 cm

‘Vc=o’
and its ultraviolet spectrum (95% ethanol) has a maximum
at 292 mu (8 1290) with shoulders at 313 (a 800), 301 (5
1230) and 247 mu

(8 2980) . The nmr spectrum of '62, in CCl4

(Figure 12) consisted 'of three-proton singlets at T 9.50,

9.00, 8.80, 8.77, 8.58 and 8.50 and an aromatic multiplet,
T 2.92-3.08 (4H) .

Anal. Calcd. for,C18H2202 C, 84099; H, 8.72

Found: C, 84.73; H, 8.59.

 

 

66

IHm.«o.o.m.mioaowofluuoucmnlb.olawnuomemslw.m.m.m.N.H mo AvHUUV Esuuowmm HEZ

.AMWV oCOIVIConluoo

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

.NH ouooem
no. m r n v n a
. a . a . a e
__ ._
M l _ g
i l i i f
l r i . ,+
M ”w n .T
._ __ i L
_ _ __ __
l .:
_ T a
. _fiu
F_

 

67

Beduction of 1 , 2 , 3 , 3 , 5 , 8-Hexamethyl-6 , 7-benzotrigyclo-

[3 .3 .0 .02! 8] oct-6-en-4-one (69) with Lithium Aluminum
’ der ide

 

A solution of 32 mg of 62 in 2 ml of dry tetrahydro-
furan was added to a suspension of 474 mg of lithium aluminum
hydride in 4 ml of dry, refluxing tetrahydrofuran.

The mix-
ture was refluxed for 27 hrs, then cooled in an ice bath,

 

and small pieces of ice were added to hydrolyze the excess

lithium aluminum hydride.

In;- “T‘s E‘.

To this mixture was added 10 m1
of water.

The resulting mixture was extracted with ether

 

(3 x 20 ml) and the separated ether layer was dried over

('A :'

anhydrous magnesium sulfate. Evaporation of the ether solu-

tion provided a solid which when examined by Vpc (10‘ x 1/4“

FFAP column; 220°; 100 ml/min of He) indicated a single re-
duction product. The compound was purified by vpc (above

conditions) and has been identified (mp, ir spectrum, Rt)
as 1,2,3,3,5,8-hexamethyl-6,7-benzotricyclo[3.3.0.02:3]-

oct-6-en-syn-4-ol, 9.9» (see Section S for Spectral character-

istics and analysis).

SUMMARY

1 . Irradiation of an ether solution of 1,3,3,4,7,8-

hexamethy 1-5 , 6-dicarbomethoxybicyc lo [ 2 .2 .2] octa-5 , 7 -dien-

2—one (32’) provided an 80% yield of dimethyl 3,4,5,6-

tetramethylphthalate (3’1”). Irradiation of 1,3,3,4,7,8—

hexame thyl-5 , 6-dipheny lbicyclo [ 2 .2 .2] octa-5 , 7-dien-2-one
(32") under identical conditions gave an 83% yield of

3 , 4 , 5 , 6-tetramethyl-1 , 2-diphenylbenzene (3'3") .

2. When a solution of 3,2, in 2-methyltetrd1ydrofuran was ir-

radiated for Short intervals at -100° in a sodium chloride

cavity cell, the formation of dimethylketene was detected

spectroscopically (infrared).

3. Irradiation of an ether solution of 1,3,3,4,7,8-hexa-

methyl-5,6-benzobicyclo[2.2.2]octa-5,7-dien-2-one (42) af-

forded an 82% yield of 1,2,3,4-tetramethylnaphthalene (31)

and a 13% yield of 1 , 4 , 4 , 5 , 6 , 7-hexamethyl-2 , 3-benzobicyclo-

[3.2.0]hepta-2,6-diene (48'). Irradiation of 3,3,7,8-tetra-

methyl-5 , 6-benzobicyclo [2 .2 .2] octa-5 , 7-dien-2-one (5,6,)

under identical conditions gave a 70% yield of 2,3-dimethyl-
naphthalene (51) and an 8% yield of 4,4,6,7-tetramethyl-
2 ,3-benzobicyclo[3 .2 .0] hepta-2 , 6-diene (58') .

68

 

 

69

4. Irradiation of 4,6, with acetone sensitization provided

not only a 45% yield‘of ’41 and a 6% yield of 49, but also
a 26% yield of 1,2,4,4,5,8-hexamethyl-6,7-benzotricyclo-

[3.3.0.02'8]oct-6-en-3-one (99'). Similarly, acetone-sensi-

tized irradiation of ’59 gave’a 66% yield of ’51, a 6% yield
of 99, and a 9% yield cf 1,2,4,4-tetramethy1-6,7-benzotri-

cyclo[3 .3 .0 .02 , 8] oct-6—en-3-one (22.) .

5. The photoisomerization of 49 to 28. and of 99 to 29 was

shown to occur from the triplet State of the keténes Via
1,2-acyl migrations.

6. Acetone-sensitized irradiation of 1,3,3,4,7,8-hexa-
methyl-5,6-benzobicyclo[2.2.2]octa-5,7-dien-§nEi-2-ol (99)
afforded a 73% yield of a 3:2 mixture of 1,2,3,3,5,8-hexa-
methyl-6,7-benzotricyclo [3 .3 .0 .02 ' 8] oct-6-en-ar_1_t_i_-4-ol (9'2)
and 1,2,4,4,5,8-hexamethyl-6,7-benzotricyclo[3.3.0.03'°]-
oct-6-en-agti-3-ol (99). However, acetone-sensitized ir-
radiation of 1,3,3,4,7,8-hexamethyl-5,6-benzobicyclo[2.2.2]-
octa-5,7-dien-§yg-2-ol (9;) provided the single photoisomer

1 , 2 , 3 , 3 , 5 ,8-hexamethyl-6 , 7-benzotricyclo[3 .3 .0 .02 r 8] oct-6-

en-syn-4-ol (99) .

7. Oxidation of the syn alcohol 99 or the anti alcohol

99' with chromium trioxide-pyridine "gave 1 ,2 ,3 ,3 ,5 ,8-hexa-
me thyl-6 , 7-benzotricyclo[3 .3 .0 .02 I 3] oct-6-.en-4-one (99) .

However, reduction of ketone f69with lithium aluminum'hy-

dride afforded only the syn aloohol 99.

70
8. Oxidation of anti alcohol 99with chromium trioxide-
pyridine provided ketone 99. Reduction of ketone 99 with

lithium aluminum hydride only gave anti alcohol 99'.

PART II

 

THE PHOTOISOMERIZATION OF

1(2H)-NAPHTHALENONES :

 

 

71

INTRODUCTION

The photochemistry of 2,4-cyclohexadienones has at-

tracted considerable attention since 1960, and has been
the subject of several reviews (13,61-63). In a pioneering

study, Barton and Quinkert (64) elucidated three types of

photochemical transformations of 2,4-cyclohexadienones

having blocked ortho-positions. They found that the most

common process in the photochemistry of 2,4-cyclohexadi-
enones is ring fission of 105 to provide a ciS-diene

ketene, 106. Collins and Hart (65) established that it is
this cis-diene ketene that subsequently reacts with an

available nucleophile to give the observed product, 107.

The ease with which this reaction proceeds depends on the

 

 

I R1 0
/
R , /
4 ‘ 2 _ hV R4\¢C )1
< > I R2
A
105 \ 106
3

R4 R1 R4
/ _ \
0 R2
R2
R3
R3 '3
108 109 107

72

 

 

73
number and positions of the substituents in the 2,4-cyclo-
hexadienone and on the nucleOphilic character of I-IX.
In the absence of a strong nucleophile the reaction may
fail, and recyclization of the gisfdiene ketene permits
minor (and presumably slower) processes to become important,
namely the formation of phenols, either by a dienone/phenol
photorearrangement to give EQQ; or by homolytic photodissoci-
followed by hydrogen abstraction from the solvent,

ation,

to yield 109. The dienone/phenol photorearrangement re-

quires R2 to be a nucleophilic group. Thus irradiation

of 2,4,6-trimethyl-6-acetoxy-2,4-cyclohexadienone (105:
R2 = OAc; R1 = R3 = R4 = Me) in dry ether, or in the presence

of water or aniline gave 3-acetoxy mesitol (108: R2 = OAc.

R1 = R3 = R4 = Me), whereas an analogous compound (122;
R2 = allyl, R1 = R3 = R4 = Me) did not undergo such a re—
arrangement.
Recently Hart and his co—workers have reported that
certain alkyl-substituted 2,4-cyclohexadienones undergo

specific photoisomerization to bicyclo[3.1.0]hexenones to

the complete exclusion of ring-opened products, even with

alcohols as solvent. Thus hexamethyl- and hexaethyl-2,4-

qyclohexadienones (gg'and 110, reSpectively) are photoisom-
erized to bicyclo[3.1.0]hexenones 111 and 112, respectively

(24,66). However, this photorearrangement is sensitive to

the position and number of alkyl substituents in the

74

O R 0

R I R R R
R
hv
———>
R

R R R R

R
gg, R = CH3 111, R = CH3
11 ,wR = CHZCH3 112. R = CH2CH3

cyclohexadienone. For example, although pentamethylcyclo-

hexadienone 113 is photochemically inert in ether, irradia—

tion of 113 in methanol gave 114 (67), the ring—opened
product expected from a cis—diene ketene intermediate.

irradiation of the isomeric pentamethyl cyclohexa-

However ,
o
H
-93———> (CH ) c = c - c = c - CH co CH
CH30H 3 2 u ' ' 2 2 3
CH3 CH3 CH3
113 114
W W

dienone 115 in ether or methanol provided 116 exclusively

(67).

O
O

H
hv >
CH30H .”

 

H

H

U"
H
H
05

§

75

Griffiths and Hart (26) have now shown that in all

these cases the only photochemical reaction is ring opening

to a ketene and that all other processes, including isomeri-

zation to a bicyclo[3.1.0]hexenone, are thermal. The cis-

diene ketene intermediate, 117, was detected spectroscopi--

aflly at low temperatures and could be trapped.even at room

temperature, by the inclusion of a strong nucleophile in
the photolysis solution. Thus irradiation of gfi in alcohol
or hexane with dimethylamine present provided amide 118 in

high yield (26) Similar observations have been made by

 

 

C470 O
// ./’
M I A n
< > —>
A \
gs, 117 111
1(CH3)2NH
o

(CH3)2 c = c — c = c - CH - c - N(CH3)2
CH3 CH3 CH3 CH3
118

Perst and Dimroth (68) in a report concerning the photo-

chemistry of 2,4,6-triphenylfi2fquinolesters. Further

studies by Griffiths and Hart (26,69) suggest that the
‘photochemical cleavage of the 1,6-bond in 2,4-cyclohexa-

dienones to form cis-diene ketenes occurs efficiently (but

not necessarily exclusively) from the n,7r* singlet state

of the dienone.

76
Most recently it has been established by Hart and

Griffiths (69) that the photoisomerization of a 2,4—cyclo-
hexadienone to a bicyclo[3.1.0]hexenone can be effected
directly, i;g;, without the intermediacy of a ketene. For
example, although 3,4,6,6—tetramethyl—2,4-cyclohexadienone,
Q6, is photochemically inert in non-nucleophilic solvents
(29), and gave only ketene—derived ethyl 3,4,6-trimethyl-
hepta-3,5-dienoate, 112“ when irradiated in ethanol (29),
it was readily photoisomerized in trifluoroethanol or on

silica gel to the isomeric bicyclic ketone 120. The

 

o
o
hv > (CH ) C=CH-C = c — CH —5-OEt
CH3CH20H 3 ? , . 2
CH3 CH3
gg' 119

o

hv H

CF3CH20H

 

 

.. t? fl>

silica gel
20

rm

authors suggest that the photoisomerization proceeds from
the first v,v* singlet state of the dienone. Thus the
.major requirement necessary to effect this photoisomeriza-
tion directly is that the dienone be sufficiently perturbed
by medium effects to bring about inversion of the n,1r*

and first. wyv* singlet states.

77
Immorder to study the influence on the photochemistry
of highly substituted 2,4-cyclohexadienones when one of the
two carbon-carbon double bonds of the cyclohexadienone sys-
tem belongs to a fused aromatic ring, we synthesized naphtha-

lenones 121 and 122 (50,53). As previously reported by us

0
O
121 12,2"

(50), no volatile products could be detected from the
photolysis of naphthalenone 122.1“ ether or methanol.
However, irradiation of naphthalenone lzl'in ether provided
the benzobicyclo[3.1.0]hexenone lzg'as the primary photo-
Further irradiation of 12} in ether gave naphtha-

product.

lenone 124. An investigation of the mechanisms for the

O O
00 h“ O»

123 333

 

 

121

 

 

> 124 is the

 

photoisomerizations 121 > 123 and 123

subject of Part II of this thesis.

RESULTS AND DISCUSSION
A. Mechanistic Considerations

In view of previous mechanistic photochemical studies
of 2,4-cyclohexadienones, three gross mechanisms can be
suggested to account for the photoisomerization of 2,2,3,4—
tetramethyl-l(2H)-naphthalenone,1glx to 1,5,6,6-tetramethyl-

3,4—benzobicyclo[3.1.0]hexen—2-one, 123. One likely

O

 

 

121 123

(WV rwv

mechanism is photochemical cleavage of the 1,2-bond in .
naphthalenone 121 and electron reorganization to provide
the ketene intermediate 122; Such a ketene intermediate
could thermally cyclize to the starting naphthalenone EEL

or to the observed product, benzobicycloketone 123.

 

 

0 O
//' /
<———
A \
121 125 £51

78

79

As discussed in the Introduction, Griffiths and Hart (26)
have shown that an analogous mechanism is operative in the
photoisomerization of 2,4-cyclohexadienones to bicyclo-
[3.1.0]hexenones gig the n,w* singlet state of the dienone.

The conversion of lzl'to lzg'can also be formulated as
proceeding yi§_a "bond-crossing" mechanism that does not
involve the intermediacy of a ketene. Such a mechanism is
presented below. Ionic intermediates are used for conveni-

ence .

 

 

D
‘V
;1

§

Such a mechanism is tenable, as Griffiths and Hart (69) have

found that 2,4-cyclohexadienones can be directly photoisomer-

 

ized to bicyclo[3.1.0]hexenones yi§_the first w, w* sing-
let state of the dienone, if the dienone can be sufficiently
(perturbed by medium effects to cause inversion of the n,v*
and first v,w* singlet states.

Finally, the photoisomerization of 121 to lgg'can be

rationalized by a mechanism involving migration of a

. «.J: ‘1"?

 

80

methyl group from C—2 to C-3 in intermediate 126, as shown

 

 

below.
0 -
hv
>
122. Egg. E!
lACHa g3
_ f
‘f 01 :
h» < 36 ,
£1
222,

Although the primary photoproduct from the irradia-
tion of naphthalenone 121 in ether is benzobicycloketone

123, continued irradiation of 121 provides naphthalenone

124 (50). Independent irradiation of an approximately
0 o o
I
121 123 124

0.5% solution of benzobicyckfl3.1.0]hexenone 123 through a
Pyrex filter provided an 80% yield of naphthalenone 124.
Thus 123 can be considered as the intermediate in the photo-

isomerization of naphthalenone 121 to naphthalenone 124.

81
Although a much more common photochemical reaction is
the photorearrangement of 2,5-cyclohexadienones to bicyclo-
[3.1.0]hexenones (13,63,70), a few cases of photoisomeriza-
tions of bicyclo[3.1.0]hexenones to 2,5-cyclohexadienones
have been reported. For example, Schuster has shown that

irradiation of 127 provides 2,5-cyclohexadienone 128 (77).

 

   

128

similarly, Jeger and his co-workers have reported that ir—
radiation of 129 gives a mixture of 2,5-cyclohexadienones

131 and 132, presumably via the ionic intermediate 130 (72).

 

 

 

131 132

82
In each of these cases the photoisomerization proceeds by
an apparent 1,2-methyl migration. As depicted below, an

analogous mechanism would account for the photoisomerization

of 123 to 124.

M

 

V

3“"3‘5 ‘1‘. K ’ ‘l .' 7
J

 

want
«nun-in: _

 

 

In a preliminary investigation, it was found that ir-
radiation of bicyclo[3.1.0]hexenone 111 in ethanol gives

hexamethyl-2,5—cyclohexadienone, 133. However, Hart and

111 1252.

Swatton (73) have shown that photolysis of 111 in methanol

through Pyrex initially gives methoxyenol 135. This product

83
is considered to result from the trapping of a dipolar

intermediate (134) by the solvent. Methoxyenol 135 readily

 

, - OH
0 c1130
hv CH30H
> '—'—_——>
m
111 134 135 -

 

 

 

133 136

loses methanol (thermally or in acid) to afford the enolic
triene 132; which gives 122,0“ further treatment with acid.
Of course the photoisomerization of benzobicyclo[3.1.0]-
hexenone l£§.t° naphthalenone lgg'can be rationalized by a
similar mechanism (for details, see Section C). However,
it should be noted that the acid-catalyzed rearrangement of
lgg'to lgg'requires a 1,2-methyl migration. Therefore, for
the photoisomerization of 123 to lgg'to proceed by either
of the mechanisms already presented, a 1,2-methyl migration
is necessary.

The conversion of lgg'to naphthalenone lzé'can also be
explained by a "bond-crosSing" mechanism, as is shown below.
In such a mechanism the methyl substituents retain their

original positions.

84

 

123

O

 

 

124

B. The Photorearrangement of 2,2,4-Trimethyl—1(2H)-
naphthalenone (136) '

 

In Part A three discrete mechanisms were advanced to
account for the reported photoisomerization of 2,2,3,4-tetra-
methyl-1(2H)—naphthalenone, 121” to 1,5,6,6-tetramethyl-
3,4-benzobicyclo[3.1.()]hexen-2-one, 122; These mechanisms
can be differentiated by an examination of the photorear-
rangement of 2,2,4-trimethyl-1(2H)-naphthalenone, 132;
Photoisomerization of naphthalenone lgg'yig_ketene inter-
mediate lgz'would be expected to yield benzobicycloketone
138; The same benzobicycloketone photoproduct would be

expected if the rearrangement occurred by a "bond-crossing"

 

85

 

o O
H
.>

m m. 1:18.

mechanism that did not involve a ketene intermediate, i.e.,

via 139. However, photoisomerization of 136 by a mechanism

 

that required a 1,2-methyl migration would give a different

photoproduct, benzobicycloketone 140.

 

86

O
lllllli'llff ihv
—"—>
H
136

1~CH3
o 0

0‘8;—

140

R 1&0

A reasonable synthesis for the desired naphthalenone
lfig appeared to be the electrophilic oxidation of 1,2,4-
trimethylnaphthalene. In a series of recent reports (24,
29,67), Hart and his co-workers have shown that oxidation
of highly alkyl-substituted benzenes with electrophilic oxi-
dants proceeds with Wagner-Meerwein rearrangement to give
the correSponding cyclohexadienones in excellent yields
(74). For example, oxidation of hexamethylbenzene with
peroxytrifluoroacetic acid-boron fluoride gave a 90% yield
of hexamethyl-2,4-cyclohexadienone (24), and the major
products from the oxidation of pentamethylbenzene are also
dienones (67). Similarly, oxidation of 1,2,3,4-tetramethyl-
.naphthalene with peroxytrifluoroacetic acid—boron fluoride
etherate in methylene chloride provided naphthalenones 121
and 122.3nd the tetramethyldioxotetralin 141 in the ratio

of 61:21:18 with an overall yield of 50% (50).

87

 

12.1, 122. 1.22,
1,2,4-Trimethylnaphthalene was prepared gig a modifica- P}
tion of the method of Hewett (51). 1,2-Dimethylnaphthalene E3
was chloromethylated with paraformaldehyde and hydrogen %
chloride in acetic acid. Hydrogenolysis of the resulting l
1-chloromethyl-3,4-dimethylnaphthalene with lithium aluminum i;

hydride in tetrahydrofuran provided 1,2,4-trimethylnaphtha-
lene (Hewett used catalytic hydrogenolysis).
1,2,4-Trimethylnaphthalene was oxidized at -20° to
-100 with a 10% excess of peroxytrifluoroacetic acid in
methylene chloride. Boron fluoride etherate was added at a
molar rate equal to that of the oxidant. ~These conditions
effected an 83% conversion of 1,2,4—trimethylnaphthalene.
The volatile products were separated by distillation and
column chromatography and finally purified by Vpc. The com-
position of the distillate consisted of unreacted 1,2,4-tri-
methylnaphthalene (42%), 2,2,4-trimethy1-1(2H)-naphthalenone,
(122, (47%), 1,1,4—trimethyl—2(1H)-naphthalenone, 122/ (9%)
and an unidentified product (2%). The structures of the
products follow from their analyses, spectral properties,

and mode of formation.

88

Ill!I I’D
H ‘ H

136 142

NW
(M

:0

Examination of Table II shows that the infrared and

«IT'-
.'£L. ‘P:

ultraviolet spectra of naphthalenone 136 compare very favor-

“ ‘32 iii—it
1 '~

ably with the data previously reported for tetramethyl-

naphthalenone 121 (50). The nmr spectrum of 136 consisted

 

of a sixhproton singlet at T 8.78 (ggmfdimethyl group), a U
three-proton doublet (J = 1.5 Hz) at T 7.89 (allylic methyl
split by a neighboring vinyl proton), a one-proton quartet
(J = 1.5 Hz) centered at T 4.15 (vinyl proton split by al-
lylic methyl), and aromatic multiplets, T 2.30—2.90 and T
1.85—2.10 (4H together).

Inspection of Table III indicates that the infrared
and ultraviolet spectra of naphthalenone léz’also compare
favorably with the data previously reported for tetramethyl-
naphthalenone 122 (50). The nmr spectrum of 142 contained
a six-proton singlet at T 8.62 (ggmfdimethyl group), a
three-proton doublet (J = 0.9 Hz) at T 7.68 (allylic methyl
split by a neighboring vinyl proton), a broad (hw = 4.0
cycles) one-proton singlet at T 4.03 and an aromatic multi-
plet, T 2.51-2.86 (4H).

A reasonable mechaniSm for the formation of the oxida-

tion products is presented in Figure 13. For simplicity

89

Table II. The infrared and ultraviolet spectra of 1(2H)-
naphthalenones 121 and 136

 

 

 

 

 

o 0
I
121 136
Infrared Spectra
(liquid film) 12;! £23
-1 ‘
vczo, cm 1674 1673
v . -1
c=c (conj), cm 1633
-1
VCZC (arom), cm 1600 1600
Ultraviolet Spectra
(95% Ethanol) Amax' mu (109 8) kmax. mu (log 8)
340 (3.14) 333 (3.23)
286 (3.33) 283 (3.35)
276 (3.49) 274 (3.56)
268 (3.49) 266 (3.54)

239 (5.05) 236 (4.53)

 

.$57

'TW'mE-"QTR' -

G4" -

.
fl . ‘

90

Table III. The infrared and ultraviolet spectra of 2(1H)-

naphthalenones 122 and 142

0./ O

(“"43 V

 

 

 

 

 

 

122 142
Infrared Spectra
122, liquid film 122 142
1422 CC14 soln.
—1
cho' cm . 1652 1660
. —1
vc=c(conj), cm 1621 1628
-1
vc=c(arom), cm 1600 1604
Ultraviolet‘Spectra
(95% Ethanol) xmax’ mu (log 8) kmax’ mu (log 8)
308 (3.91) 304 (4.10)
239 (3.95)' 238 (4.09)
234 (3.97) 234 (4.09)

 

91

 

.mcmamsunmmchzuoE
IHHuIV.N.H mo muoscoum coaumoflxo may mo soflumEHom on» How Emflsmzowe 4 .mH ousmflm

mvfi owfi 04H
m m m
+|I|I Mullllm.
o +mumo mo.z .
m
NOUQWUI
maoonmo
mmH vvfi we“

3 . m
T) T)
_ .7 ml ”mu 2
NO 03

92
the mechanism is written using OH+ as the oxidant, although
it is recognized that the positive hydroxyl species may
have trifluoroacetate or other ligands attached (74).
Strong evidence has been presented by Norman and Davidson
supporting the intermediacy of an electrophilic, cationic
reactant in;perOthrifluoroacetic acid oxidations (75).

Naphthalenone lgg'is presumably formed by electro-
philic attack of peroxytrifluoroacetic acid at C-1 of
1,2,4—trimethylnaphthalene, leading to the intermediate
carbonium ion 142; WagnereMeerwein migration of a methyl
group to C-2 would provide carbonium ion 124“ and loss of
a proton would give naphthalenone 132; Similarly, the forma-
tion of naphthalenone lgg'is accounted for by attack of the
electrophilic oxidant at C-2 of 1,2,4-trimethylnaphtha1ene,
leading to carbonium ion 122; Migration of a methyl group
to C-1 would afford intermediate carbonium ion 142“ and loss
of a proton would give naphthalenone kgg.

Having successfully prepared naphthalenone 136, the
photochemistry of this compound was investigated. The ir—
radiation of a solution of naphthalenone 132 in anhydrous
ether through a Pyrex filter with a Hanovia L 450dw lamp
was monitored by vpc. Photolysis led to a decrease in the
concentration of naphthalenone 132 and the appearance of a
photOproduct, 141/ that reached a maximum concentration of
11% of the volatiles after three hours irradiation, and
then decreased as the phOtolysis was continued. Another

photoproduct, 148, was also detected and the concentration

93
of lgg'continued to increase until the photolysis was ter-
minated. After 12 hours irradiation, vpc analysis of the
photolysate indicated the volatiles were composed of:
naphthalenone 132 (18%), 121 (3%) and 148 (78%). Photo—
product lgg'has been identified as 3,4,4-trimethyl-1(4H)-

naphthalenone. In View of the known photochemistry of

O
I . H
o u o
H

136 148

NW

 

 

2,2,3,4-tetramethyl-1(2H)—naphthalenone, 12;, (described in
detail in Section A), photoproduct 121.is presumed to be a

benzobicyclo[3.1.0]hexenone. ‘However, it was not trapped,

nor was its structure investigated.

Naphthalenone 128 was an oil that showed conjugated
carbonyl and double-bond absorptions in the infrared region
at 1660 and 1632 cm_1 respectively. The nmr spectrum of
Igfi'consisted of a six-proton singlet at T 8.52 (ggmedi-
methyl group), a three-proton doublet (J = 1.5 Hz) at T
7.91 (allylic methyl split by a neighboring vinyl proton),
a one-proton quartet (J = 1.5 Hz) centered at T 3.85 (vinyl
proton split by allylic methyl) and aromatic multiplets,

T 2.45-2.85 and T 1.85-2.10 (4H together). The identity

of naphthalenone 148 was firmly established by comparison

of the 2,4-DNP derivative of 148 with an authentic sample

94

of the 2,4—dinitrophenylhydrazone of 3,4,4-trimethyl-
],uLH)-naphthalenone prepared independently by Huffman

and Bethea (57,58).

As previously shown, photoisomerization of naphthalen-

one 136 to a benzobicyclo[3.1.0]hexenone via a ketene inter—

mediate or by a "bond-crossing" mechanism that does not
involve a ketene intermediate would be expected to yield
benzobicycloketone 138; However, the photorearrangement
of lgg'by a mechanism that requires a 1,2-methyl migration
would give benzobicycloketone 142; The photorearrangement
of 12§,t° naphthalenone 148 could also occur by either of

two mechanisms, a "bond-crossing" mechanism (Path A) or

by a 1,2-methyl migration (Path B). However, photoisomeri-

zation of benzobicycloketone 140 to a 1(4H)-naphthalenone

0 O

H 'H
O» h, A
Path A ’

138

C»
"W l
O H T“ Q

148

 

 

95

138

V m
'0,
0’
(1'5"
D‘<
m
V
O
51
a
II:

 

)5 O
I
I
O

Q. 9

vn>uld be expected to ultimately provide 2,3,4-trimethyl—1-
naphthol, 149, by a "bond-crossing" mechanism (Path C)
and a mixture of 149 and naphthalenone 150 via a mechanism

involving a 1,2-methyl migration (Path D).

O
.> M >
H Path C
140
OH

—>

 

A

149

96

 

jjiiig=fla
:1:
’U
m
n-
D’ :3‘
<
- U
v
/;| l O
l
m

 

140
"""' ~H l
_ “'CHa
O 0'.
y.
H i
l H l *
O '0 fig
|
‘__> 149
H
H
150

As the photoproduct isolated in the photoisomerization
of naphthalenone l§§.is naphthalenone 148” the intermediate
benzobicyclohexenone in the conversion of lgg'to 148 must
be 5,6,6-trimethyl-3,4-benzobicyclo[3.1.0]hexen-2-one, 122;
Therefore the photorearrangement of a 1(2H)-naphthalenone
to a benzobicyclo[3.1.0]hexenone cannot involve methyl
migration, and must occur either gig a‘ketene intermediate
or by a "bond—crossing" mechanism that does not involve the
intermediacy of a ketene.

Hart and Griffiths were successful in trapping the
ketene intermediate 111 in the photoisomerization of hexa-

methyl-2,4—cyclohexadienone, 2§u to ketone 111 (26) by the

97

inclusion of a strong nucleophile in the photolysis solution.

'Phus irradiation of 28 in alcohol or hexane with dimethyl-

amine present provided amide 118 in high yield. However,

{#6 I» fie

111
7‘l(CH3)2NH
o
(CH3)2C = c - c = c - CH— c - N(CH3)2
CH3 CH3 CH3 CH3

 

 

118

similar irradiation of a hexane solution of tetramethyl-
naphthalenone 121 with an excess of dimethylamine present

‘was found to give only benzobicycloketone 123. No other

hexane >[::::1:if:]:§<<:
(CH3) 3NH

121 123

products could be detected by vpc or nmr analysis of the
photolysate.

One explanation for this result is that a ketene inter-
mediate is not involved in the photoisomerization of lzl'to

123. Contrarily, it can be contended that the reaction

 

98

does proceed by a ketene intermediate, but due to the strong
driving force for rearomatization of the ketene, it thermally
cyclizes to lgl'or 123 faster than it reacts with an avail-
able nucleophile. However, Cava and Spangler have reported
trapping a closely related ketene with a weaker nucleophile
than dimethylamine (76). Thus benzocyclobutenone, 121, is

smoothly converted to methleQ-toluate, 153, by irradiation

:1 .76.,

in methanol. The reaction is rationalized as proceeding via

rum- .el—Pn '7‘ a}??? "03(9); a J.

 

o

/ ,0 c¢ com,
I hV > 0 CH30H>

\‘ CH2 CH3

151 152 153

ketene 152. In a similar experiment, irradiation of a
methanol solution of naphthakmaua 121 proceeded via benzo-

bicycloketone 123 to provide a high yield of 124. No other

 

O
hv >
CH30H
1 1 124

products were detected by vpc or nmr analysis of the photoly-
sate.
Therefore it is concluded that the photoisomerization

of a 1(2H)-naphthalenone to a benzobicyclo[3.1.0]hexenone

99

most likely occurs by a "bond-crossing" mechanism that does
not involve the intermediacy of a ketene. Hart and Griffiths
have recently shown that the photoisomerization of a 2,4—
cyclohexadienone to a bicyclo[3.1.0]hexenone from the
first w,w* singlet state of the dienone proceeds by an
analogous mechanism.

Throughout this discussion, the photochemistry of 1(2H)- Pa
naphthalenones has been compared to that of 2,4-cyclohexa—
dienones. However, if the T electrons of the aromatic

ring in 1(2H)-naphthalenones do not influence the photo-

 

chemistry of these compounds, then the photochemistry of U
1(2H)-naphthalenones can be compared to that of 3-cyclo-

hexenones. Williams and Ziffer have shown that the charac—

teristic photoreaction of 3-cyclohexenones in solution is

isomerization to bicyclo[3.1.0]hexanones (8,9). For ex-

ample, irradiation of a tfbutyl alcohol solution of 5

through Pyrex provided Q'in good yield. Thus the photo-

hv

Si 2

rearrangement of 3-cyclohexenones is similar to that found

for 1(2H)-naphthalenones.

100

C. The Photorearrangement of 4-Ethyl—2,2—dimethyl-1(2H)-

naphthalenone (154)

 

As discussed in detail in Part A, the observed photo-
chemical conversion of benzobicycloketone 123 to naphtha—
lenone 124 can be formulated as proceeding by a 1.2-methyl

migration, or the methyls may retain their original positions

 

 

I
o o L
I ..
on» M 00 i
i
12.5 5222.

and the rearrangement may be of the "bond-crossing“ type.
These alternative mechanisms can be differentiated by an
examination of the photorearrangement of 4-ethyl-2,2-di-
methyl-1(2H)-naphthalenone, £24.

In Part B it was established that the photoisomeriza-
tion of a 1(2H)-naphthalenone to a benzobicyclo[3.1.0]—
hexenone occurs by a "bond-crossing" mechanism. Thus ultra-
violet irradiation of naphthalenone 124 will provide ketone

155. Photoisomerization of 155 by a mechanism that required

0

0
OD ——*” > .
H 1

101
a 1.2-methyl migration would be expected to give naphtha-

lenone 156. However, photorearrangement of 155 by a “bond-

 

O O-
H H
0.} hv _>
2'53 I
1.....3 ,
O ."
*H q

156

crossing" mechanism would be expected to yield another

product, naphthalenone 157.

O.» hv > so»
155
w I

 

\
A
1

 

H
U1
q

102

A suitable synthesis for the desired naphthalenone 122'
appeared to be the electrophilic oxidation of 4-ethyl-1,2-
dimethylnaphthalene, lgfif 1,2—Dimethylnaphtha1ene was acetyl-
ated with acetyl chloride—aluminum chloride at 00 (59).
Clemmenson reduction of the resulting 1-acetyl-3,4-dimethyl—
naphthalene provided 4-ethyl-1,2-dimethy1naphthalene.

4-Ethyl—1,2-dimethylnaphthalene was oxidized at -200

to -10° with a 10% excess of peroxytrifluoroacetic acid in

5".“ o‘-‘ “Sq

methylene chloride. Boron fluoride etherate was added at

a molar rate equal to that of the oxidant. These conditions

rum-4
‘1

effected a 78% conversion of 4-ethy1-1,2-dimethylnaphthalene.
The volatile products were separated by distillation and
column chromatography and finally purified by vpc. The
composition of the distillate consisted of unreacted 4-
ethyl-l,2-dimethylnaphthalene (41%), 4-ethyl-2,2-dimethyl-
1(2H)-naphthalenone, 152, (49%), and 4—ethyl-2,2-dimethy1—

2(1H)—naphthalenone, 159, (10%). The structures of the

o
0’ O. O
H~ H
154 159

products follow from their analyses, spectral properties,
and mode of formation.
Naphthalenone 154 was an oil that showed principal in-

frared bands (CC14) at 1675 (v conjugated), 1640

C:O'

103

(shoulder, vczc) and 1600 cm.1 aromatic). The

(chc'
ultraviolet spectrum of lgg'in 95% ethanol had maxima at
333 (log 5 3.32), 283 (log 5 3.42), 274 (log 5 3.61), 266
(log e 3.61) and 236 mu (log a 4.74). Inspection of Table
II shows that the infrared and ultraviolet spectra of
naphthalenone lgg'compare favorably with the data previously
determined for similarly substituted 1(2H)-naphthalenones.
The nmr spectrum of 122 contained a six-proton singlet at
T 8.80, a three-proton triplet (J = 7.8 Hz) centered at
T 8.80, a two-proton quartet (J = 7.8 Hz) centered at T
7.50, a broad (hw = 3.3 cycles) one-proton singlet at T
4.25, and aromatic multiplets, T 2.55-3.13 (3H) and 2.0-
2.2 (1H). The nmr spectrum of yég is consistent with the
assigned structure.

Naphthalenone 122,W35 also an oil that had infrared
bands (CC14) at 1660 (v

conjugated), 1622 (vC con-

=C'

aromatic). The ultraviolet

C=O,
jugated) and 1602 cm-1

(VC=C’
spectrum of lgg'in 95% ethanol showed maxima at 303 (log 5
4.11), 237 (log 5 4.10) and 232 mu (log a 4.10). The in-
frared and ultraviolet spectra of naphthalenone 152.compare
well with the data previously obtained for similarly sub-
stituted 2(1H)-naphthalenones (see Table III). The nmr
Spectrum of lég'consisted of a three-proton triplet (J =
7.8 Hz) centered at T 8.69, a six-proton singlet at T 8.62,
a two-proton quartet (J = 7.8 Hz) at T 7.29, a broad one-

proton singlet at T 4.07, and an aromatic multiplet, T

2.48-2.95 (4H).

_' 7&1? 'v “‘1‘ l .nmu

\rues.
+1..

104

Having prepared the desired naphthalenone 122“ the
photochemistry of this compound was examined. Irradiation
of a solution of naphthalenone 124 in diethyl ether through
a Pyrex filter with a Hanovia L 450-w lamp was monitored
by vpc. Photolysis produced a decrease in the concentra-
tion of naphthalenone 154 and the appearance of a photo-
product that reached a maximum concentration of 15% of the
volatiles after five hours irradiation, and then decreased
as the photolysis was continued. This photoproduct is
tentatively assigned the structure of 5-ethyl-6,6-dimethyl—
3,4-benzobicyclo[3.1.0]hexen-2-one, 122: As the irradiation
was continued, another photoproduct was also detected and
the concentration of this product continued to increase
until the photolysis was terminated. The latter compound
was isolated and has been identified as 4-ethyl-3,4—dimethyl-

1(4H)-naphtha1enone, 156..

 

 

 

.1
o F— o
H
m a
’ D
H
— __J
1.5.2, 12?, l

H
gen
05

 

105.
After 12 hours irradiation, vpc analysis of the photolysate
indicated the volatiles were composed of: naphthalenone
154'(30%), 122 (7%) and 122'(63%). In an attempt to in—
crease the yield of 125/ a solution of naphthalenone 122'
in trifluoroethanol was irradiated through a uranium glass
filter (short wavelength cut-off at about 360 mu). Vpc
analysis of the photolysis solution after brief irradiation p:
showed the volatiles were composed of: naphthalenone 124' l
(51%), 122 (11%) and naphthalenone 122'(38%). Further ir-

radiation provided an excellent yield of 156.

 

Naphthalenone 122 was an oil that analyzed well for g;
the empirical formula C14H130. In the infrared region 122'
showed conjugated carbonyl and double-bond absorptions at
1660 and 1631 cm"1 respectively. The ultraviolet spectrum
of 126 in 95% ethanol had a maximum at 252 mu (log a 4.17)
and a shoulder at 269 mu (log 8 4.07). The infrared and
ultraviolet spectra of 1§§,compare favorably with data pre-
viously reported for similarly substituted 1(4H)-naphthalen-
ones (50,57). The positions of the substituents in naphthalen-
one léé'were apparent from the nmr spectrum, which consisted
of a three-proton triplet (J = 7.8 Hz) centered at T 9.62,
a three—proton singlet at T 8.55 (C—4 methyl), a two—pro-
ton quartet (J = 7.8 Hz).centered at T 8.05, a three-proton
doublet (J = 1.5 Hz) at T 7.94 (allylic methyl split by a
neighboring vinyl proton), a broad (hw = 3.6 cycles) one-
proton singlet at T 3.79 (vinyl methyl) and aromatic multi-

plets centered at T 2.67 (3H) and T 1.93-2.12 (1H). In the

106
Imelated naphthalenone 148. the allylic methyl appears at

17 7.91. Similarly, in tetramethylnaphthalenone 124 the

O o
H
148 124 .

Eillylic methyls appear at T 8.02 and 7.93. The signal at

1C 7.93 has been assigned to the methyl at C-3, as a methyl

 

aattached to the 5 carbon of a cyclic dienone exhibits a
ILower field signal (24,71).

Since the photoproduct isolated in the isomerization
(of naphthalenone léé'is naphthalenone 126, the photorear—
zrangement of a benZobicyclo[3.1.()]hexenone to a 1(4H)-
Iuaphthalenone must occur gig a 1,2-alkyl migration. »A
:few cases have been reported in which the photoisomeriza-
‘tion of a bicyclo[3.1.0]hexenone to a 2,5-cyclohexadienone
<occurs by a 1,2-alkyl migration (72,77). -However, the photo-
rearrangement of lgé'to 126 can also be rationalized by a
lmechanism analogous to that eluciated by Hart and Swatton
for the conversion of bicyclo[3}1.0]hexenone £11 to hexa-
methyl-Z,5—cyclohexadienone (see Section A). Thus the
dipolar intermediate 122“ photochemically generated from
125“ could be trapped by a suitable nucleophile to give
16;; Thermal or acid-catalyzed elimination of the nucleo-

phile from 161 would provide the enolic triene 162, which

107

O
H
.> .22...

 

161 x

 

4A '
: .'. .
. .- .

156

W

could yield 156 on further treatment with acid.
Although Swatton was able to obtain the enolic triene
136 by irradiation of a solution of bicyclo[3.1.0]hexenone

111 in anhydrous ether at 00 (78), no intermediates have

0 OH
hv, 0°>
ether

111 136

been detected in the photoisomerization of benzobicyclo-

[3.1.0]hexenones to 1(4H)-naphthalenones.

108

D. Conclusion

 

The goal of Part II of this thesis was to determine

the mechanisms for the photoisomerization of 121 to 123 and

of 123 to 124.

 

0 O O
hv r
h, > O.» -->
L‘
22.1. L232, L212. L»,

 

Having examined the comparable photorearrangement of 2,2,4—
trimethyl—l(2H)-naphthalenone, 122, it can be concluded that
the photoisomerization of naphthalenone 12;.t0 benzobicyclo—
ketone 123 occurs by a "bond-crossing" mechanism that most
likely does not involve a ketene intermediate. Furthermore,
an investigation of the photorearrangement of 4-ethyl-2,2L
dimethyl-1(2H)-naphthalenone, 124, has shown that the photo-
isomerization of 122.t° naphthalenone 124 must proceed gig

a 1,2-alkyl migration.

EXPERIMENTAL

A. Irradiation of 1,5,6,6-Tetramethyle3,4-benzobicyclo-
[3.1.0]hexen-2-one (123) in Diethyl Ether

 

A solution of 44 mg of 122'(50) in 8 ml of diethyl
ether was irradiated through a Pyrex filter with a 450-watt
Hanovia Type L mercury arc lamp. Monitoring the photolysis
by vpc (5' x 1/4" DEGS column; 180°; 100 ml/min of He)
indicated the formation of a single photoproduct. This
compound was purified by vpc (above conditions) and was
shown to be identical [mp: 76-780; ir spectrum (CCl4):

1648 (VG-0' conjugated), 1626 (shoulder, conjugated)

vczc'

and 1605 cm-1 (v aromatic); nmr spectrum (CC14): a six-

czc'
proton singlet at T 8.52, broad three-proton singlets at

T 8.02 and 7.93 and an aromatic multiplet centered at T
2.57 (4H)] with a sample of 2,3,4,4-tetramethyl-1(4H)-
naphthalenone, 124x previously prepared in this laboratory

(53). The photoisomerization of 123 to 124 proceeded in

80% yield (vpc and nmr, hexamethylbenzene as standard).

109

 

110

B. Preparation of 1,2,4-Trimethylnaphthalene
1. 1-Chloromethyl-3,4-dimethylnaphthalene (51)

To an ice—cold solution of 1,2-dimethylnaphthalene
(60.0 g, 0.38 mole) in 200 ml of acetic acid was added 23.3
g of paraformaldehyde. -Hydrogen chloride gas was passed
through the suSpension until a clear solution resulted and
the mixture was stirred at room temperature for 16 hrs.

The solution was then diluted with water (400 ml) and ex?
tracted with benzene (3 x 200 ml). The benzene extract

'was washed with dilute sodium carbonate (3 x 200 ml) and
dried over anhydrous magnesium sulfate. After evaporation
of the solvent, the residue was distilled, bp 153-1580

(1.2 mm) providing 28.5 g (0.14 mole) of 1-chloromethyl-3,4—
dimethylnaphthalene, mp 68—710 [lit. val. (51) 70-710]. The

yield was 37%.
2. 1,2,4éTrimethylmapbthalene (51)

A solution of 1—chloromethyl-3,4—dimethylnaphthalene
(28.0 g, 0.14 mole) in 200 ml of dry tetrahydrofuran was
added over one hr to a suspension of lithium aluminum hye
dride (4.5 g, 0.14 mole) in 300 ml of dry, stirred, reflux—
ing tetrahydrofuran. The mixture was stirred at reflux for
an additional 24 hrs, then cooled in an ice bath, and small
pieces of ice were added to hydrolyze the excess lithium
aluminum hydride. To this mixture was added 150 ml of 10%

HCl and 150 ml of water. The resulting mixture was extracted

 

111
with ether (4 x 200 ml) and the separated ether layer was
dried over anhydrous magnesium sulfate. Evaporation of the
solvent provided 32.0 g of an oil which solidified with
cooling. Recrystallization of this residue from 95%
ethanol gave 12.9 g (0.076 mole) of 1,2,4-trimethylnaphthalene,
mp 48-500 [lit. val. (51) 49-500]. The yield was 55%. The

ultraviolet (54) and nmr (55) spectra of 1,2,4-trimethyl—

 

 

F
naphthalene corresponded to those in the literature.

C. The Oxidation of 1,2,4-Trimethylnaphthalene 3

i

A solution of peroxytrifluoroacetic acid (56), prepared g)

from 0.65 ml of 90% hydrogen peroxide (0.024 mole) and

5.55 g (0.026 mole) of trifluoroacetic anhydride in 10 ml

of freshly distilled methylene chloride, was cooled to —200
and added with stirring over 45 min to a solution of 3.7 g
(0.022 mole) of 1,2,4-trimethylnaphthalene in 50 ml of
methylene chloride which had previously been cooled gig a .
carbon tetrachloride-dry ice bath to -20°. Boron trifluoride
etherate (7.25 ml of 47% BF3°Et20) was added concurrently
with the addition of the peracid. The temperature of the
solution was maintained between -100 and -200 throughout

the addition. After further stirring for 45 min at —20°,

the solution was poured into 200 ml of water and the organic
layer was separated. The organic layer was washed with water
(3 x 100 ml), saturated sodium bicarbonate (3 x 150 ml),

and washed with water (3 x 100 ml). The aqueous sodium
hydroxide extract and the methylene chloride fraction were

investigated separately.

112

The aqueous base fraction was acidified with dilute
hydrochloric acid and extracted with methylene chloride
(3 x 100 ml), which yielded on evaporation 0.07 g of a dark
viscous oil. Vapor phase chromatography (5' x 1/4" 20%
DEGS 60/80 CHROM W column; 180°; 100 ml/min of He) indicated
the presence of several components. This material was not
investigated further. F

The methylene chloride fraction was dried over anhydrous
magnesium sulfate and evaporated to afford a deep red vis-

cous oil. Vacuum distillation of this material at 0.06 mm

o..'1

 

provided 1.52 g of a yellow liquid, bp 79-82°. The pot g
residue was 1.18 g of a deep red very viscous material.

Vapor phase chromatography (5' x 1/4° DEGS column; 180°;

100 ml/min of He) of the distillate showed that the crude

oil had components with the following retention times:

4.6 min (47%), 5.7 min (42%), 6.1 min (2%) and 9.8 min

(9%). The distillate was chromatographed on silica gel in

a column measuring‘ 4 x 47 cm. Elution with 1500 ml of

pentane provided 0.64 g of 1,2,4—trimethylnaphthalene which

was identified by its mp (49—510), ir spectrum, and Rt
(5.7 min). The conversion of 1,2,4-trimethylnaphthalene in
the oxidation was 83%. Elution with 600 ml of methylene
chloride provided a yellow oil which was shown to be homo—
geneous (Rt 4.6 min) by vpc (above conditions). Finally,
elution with 350 ml of 95% ethanol provided an oil which
vpc analysis indicated was composed of two compounds (R

t
6.1 and 9.8 min). Final purification of all compounds

113

was achieved by vpc. None of the compounds were found to
be thermally interconvertible under the vpc column conditions.

An insufficient amount of the product with R 6.1 min (which

t
composed 2% of the distillate) was obtained to permit identi-

fication.

1. Product Identification

 

 

k

a. 2,2,4—Trimethyl-1(2H)-naphthalenone (132). This i
colorless oil had a Rt of 4.6 min and showed principal infra- :
red bands (liquid film) at 1673 (cho’ conjugated) and 1600 :
cm_1 (VC:C’ aromatic), whereas in CCl4 solution the absorp- k

tions appeared at 1681 and 1603 cm-1. The ultraviolet
spectrum of 136 in 95% ethanol had maxima at 333 (log a
3.23), 283 (log 5 3.35), 274 (log 5 3.56), 266 (log 5 3.54)
and 236 mu (log 8 4.53). The nmr spectrum (CCl4) of 132'
consisted of a six-proton singlet at T 8.78, a threejpro-
ton doublet (J = 1.5 Hz) centered at T 7.89, a one-proton
quartet (J = 1.5 Hz) centered at T 4.15, and aromatic multi-
plets, T 2.30-2.90 and T 1.85-2.10 (4H together).

gggi, Calcd for C13H14O: C, 83.83; H, 7.58

Found: C, 83.71; H. 7.47.

b. 1,1,4-Trimethyl-2(1H)—naphthalenone (142). This oil

 

had a Rt of 9.8 min and showed principal infrared bands (CCl4)

at 1660 (Vc=0’ conjugated), 1628 (VC’C' conjugated) and

—1 . .
1604 cm (VC‘C’ aromatic).. The ultraVIOlet spectrum

of 142 in 95% ethanol Inni maxima at 304 (log a 4.10),

114
238 (log 5 4.09) and 234 mu (log a 4.09). The nmr spec-
trum (CCl4) of 122 consisted of a six-proton singlet at
T 8.62, a three-proton doublet (J = 0.9 Hz) centered at T
7.68, a broad (hw = 4.0 cycles) one-proton singlet at T
4.03 and an aromatic multiplet, T 2.51-2.86 (4H).
Aggi. Calcd for 013H140: C, 83.83; H, 7.58

Found: C, 83.69; H, 7.54.

D. Irradiation of 2,2,4-Trimethyl-1(2H)-ngphthalenone
(136) in Diethyl Ether

 

A solution of 198 mg of 2,2,4—trimethyl—1(2H)-naphtha-
lenone, 136, in 20 ml of diethyl ether was irradiated
through a Pyrex filter with a 450awatt Hanovia Type L mer-
cury arc lamp. Monitoring the photolysis by vpc (5' x 1/4"
DEGS column; 180°; 100 ml/min of He) showed a progressive
decrease in the concentration of i§§'(Rt 4.6 min) and the
appearance of two new compounds with retention times of
6.0 min and 18.6 min. The compound with Rt 6.0 min reached
a maximum concentration of 11% of the volatiles after three
hours irradiation and then decreased, whereas the concen—
tration of the compound with Rt 18.6 min continued to in-
crease as the photolysis was continued. After irradiation
for 12 hours, vpc analysis of the photolysate indicated the
volatiles were composed of: 136 (18%), a compound with R

t

6.0 min (3%) and a compound with R 18.6 min (78%). The

t

compounds were purified by vpc (above conditions). An

 

115

insufficient amount of the product with Rt 6.0 min was ob-

tained to permit identification. However, the photoproduct

with R 18.6 min has been identified as 3,4,4-trimethyl-

 

t
1(4H)-ngphthalenone, 148. This colorless oil had major

bands in its ir spectrum (CC14) at 1660 (v

C=C (VC:C'
The nmr spectrum (CCl4) of 148 consisted of a six-proton ?(

C=O’ conjugated),

, conjugated) and 1605 cm-1

1632 (v aromatic).
singlet at T 8.52, a three-proton doublet (J = 1.5 Hz)

centered at T 7.91, a one—proton quartet (J = 1.5 Hz) cen-

tered at T 3.85, and aromatic multiplets, T 2.45-2.85 and *

 

T 1.85-2.10 (4H together). Reaction of ketone £28 with (I
2,4-dinitrophenylhydrazine provided the 2,4-dinitrophenyl-

hydrazone of 128“ which was recrystallized from ethanol-

ethyl acetate to give deep violet crystals, mp 245-247°

(lit. val. (57) 243-245°). A mixture of the 2,4-DNP adduct

of the photoproduct.and an authentic sample (58) of the

2,4-dinitrophenylhydrazone of 148 also melted at 245-247°.

E. Irradiation of 2,2,3,4—Tetramethyl-1(2H)engphthalenone

(121) in Hexane-Dimethyl Amine

I

 

A solution of 114 mg (5.7 x 10'4

mole) of igi'and 64 mg
(1.4 x 10‘3 mole) of dimethyl amine in 10 ml of hexane was
irradiated through a Pyrex filter with a 450-watt Hanovia
Type L mercury arc lamp. The photolysis was monitored by
vpc (5' x 1/4" DEGS column;_180°; 100 ml/min of He). Exam—

ination by vpc of the photolysis solution after 30 min ir-

radiation indicated a decrease in the concentration of ketone

116
lzi'(Rt 7.0 min) and the appearance of a photoproduct with
Rt 3.6 min. Continued irradiation caused a progressive
decrease in the concentration of igi and a corresponding
increase in the concentration of the photoproduct. Vpc
examination of the photolysis solution after 3 hours ir-
radiation only showed the presence of compounds with reten—
tion times of 3.6 min (45%) and 7.0 min (55%). The nmr
spectrum (CCl4) of the crude photolysate after three hours
irradiation only had singlets at T 9.27, 8.84, 8.73, and
8.50, in addition to the signals for unreacted 2,2,3,4-
tetramethyl—l(2H)-naphthalenone, 121} The photoproduct was

purified by Vpc (above conditions) and has been identified

1
”mo”

(CC14): three-proton singlets at T 9.27, 8.84, 8.73, and

by its ir spectrum (CCl4): 1699 cm- nmr spectrum

8.50 and an aromatic multiplet centered at T 2.60 (4H), and
R as 1,5,6,6-tetramethyl-3,4-benzobicyclo[3.1.0]hexen-2-

t
one, 123 (50).

F. iiradiation of 2,2,3,4-Tetramethyl-1(2H)-ngphthalenone
(121) in Methanol

 

A solution of 80 mg of izi in 8 Ha. of methanol was
irradiated through a Pyrex filter with a 450-watt Hanovia
Type L mercury lamp. The photolysis was monitored by vpc
(5' x 1/4" DEGS column; 180°; 100 ml/min of He). Examina—
tion of the photolysis solution by vpc after 10 min irradi-
ation showed a significant decrease in the concentration of

the ketone 121 (Rt 7.0 min) and the appearance of a

 

117
photoproduct with Rt 3.6 min. After irradiation for one
hour, analysis by Vpc indicated the presence of only a
single photoproduct with Rt 11.5 min. The nmr spectrum
(CC14) of the crude photolysate (after irradiation for one
hour) had a sharp singlet at T 8.52, broad singlets at T
8.02 and 7.92 and a complex aromatic multiplet centered at
T 2.60. The photoproduct with Rt

by vpc (above conditions) and has been identified by its

11.5 min was purified F

mp: 76-78° and infrared spectrum as 2,3,4,4-tetramethyl-

1(4H)-naphthalenone, 124 (53). f

 

G. Preparation of 4-Ethyl-1,2-dimethylnaphthalene (158) b

 

1. l—Acetyl-S,4-dimethylnaphthalene (59)

Anhydrous aluminum chloride (106.8 g) was added to an
ice-cooled solution of 1,2-dimethylnaphthalene (62.4 g) in
carbon disulfide (450 ml). Acetyl chloride (32.0 g) was
then added dropwise to the ice-cooled mixture. After the
initial evolution of hydrogen chloride had subsided, the
reaction mixture was refluxed for 3 hrs and then left at
room temperature for 16 hours. Most of the carbon disulfide
was evaporated and the residue was poured onto a mixture of
ice and hydrochloric acid. A dark oil resulted that was
extracted with benzene (41). The benzene solution was
washed with water and dried over anhydrous magnesium sulfate.
Evaporation of the solvent provided a dark green oil that
was vacuum distilled, bp 140-143° at 0.35 mm, to give 31.6 g

of 1-acetyl-3,4—dimethylnaphthalene [lit. val. (59) bp:

118
142-143° at 0.45 mm]. Examination of the distillate by
vpc (5' x 1/4" SE-30 column; 230°; 40 ml/min of He) showed
that the 1-acetyl-3,4-dimethylnaphthalene obtained was > 95%
pure. The slight contaminant may be 3—acetyl-1,2—dimethyl-

naphthalene.

2. 4—Ethyl-1,2-dimethylnaphthalene (158)

 

1-Acety1—3,4-dimethylnaphthalene (20.0 g) was refluxed

for 27 hrs with a mixture of amalgamated zinc (70.0 g), L

concentrated hydrochloric acid (70 ml), methanol (100 ml)

 

and benzene (50 ml). While the mixture was refluxing,

*5.“-

three additional 10 ml portions of hydrochloric acid were

added. The mixture was cooled and extracted with benzene

(3 x 150 ml). The benzene solution was dried over anhydrous
magnesium sulfate and evaporated to provide an oil. Vacuum
distillation of this oil at 0.9 mm provided 11.2 g of 4-
ethyl-l,2—dimethylnaphthalene, léfiu bp 130—131° [lit. val.
(60) bp: 136° at 1 mm]. Examination of the distillate by
vpc (5' x 1/4" SE-30 column; 220°; 50 ml/min of He) showed
that the 4-ethyl—1,2—dimethylnaphthalene obtained was > 97%
pure. The ultraviolet maxima of 128 correspond exactly to

those in the literature: (95%EtOH

max 325, 290 and 232 mu (60).

The nmr spectrum of l§§,in CCl4 consisted of a three-proton
triplet (J = 7.5 Hz) centered at T 8.73, three-proton sin-
cfiets at T 7.68 and 7.58, a two—proton quartet (J = 7.5 Hz)

centered at T 7.09, a one-proton singlet at T 3.12, and

aromatic multiplets, T 2.75-2.92 (2H) and 2.15-2.31 (2H).

119

Ii. The Oxidation of 4-Ethyl-1,2-dimethylnaphthalene (158)

 

A solution of peroxytrifluoroacetic acid (56), pre-
pared from 1.53 ml of 90% hydrogen peroxide (0.055 mole)
and 12.7 g (0.06 mole) of trifluoroacetic anhydride in 20
ml of freshly distilled methylene chloride, was cooled to
0° and added with stirring over 50 min to a solution of
9.2 g (0.05 mole) of 4-ethyl-1,2—dimethylnaphthalene in 125 P
m1 of methylene chloride which had previously been cooled
gig a carbon tetrachloride-dry ice bath to -20°. Boron

trifluoride etherate (16.6 ml of 47% BF3’Et20) was added

 

concurrently with the addition of the peracid. The tem- L
perature of the solution was maintained between -10° and
-20° throughout the addition. (After further stirring for
one hour at -20°, the solution was poured into 300 ml of
water and the organic layer was separated. The organic
layer was washed with water (2 x 200 ml), saturated sodium
bicarbonate (3 x 100 ml), extracted with 10% aqueous sodium
hydroxide (3 x 300 ml)“ and washed with water (3 x 300 ml).
The methylene chloride fraction was dried over anhydrous
magnesium sulfate and evaporated to afford a deep red vis-
cous oil; Vacuum distillation of this material at 0.3 mm
provided 5.1 g of a yellow oil, bp 113-115°. The pot resi—
due was 4.0 g of a black viscous material. Vapor phase
chromatography (5' x 1/43 DEGS column; 180°; 100 ml/min of
He) of the distillate showed that the crude oil had compo-
nents with the following retention times: 4.1 min (49%),

5.4 min (41%), and 8.9 min (10%). The distillate was

120

chromatographed on silica gel in a column measuring 4 x 45
cm. Elution with 1000 ml of pentane provided 2.05 g of
4—ethyl—1,2-dimethylnaphthalene which was identified by its

ir spectrum and R (5.4 min). The conversion of 4-ethyl-

t
1,2—dimethylnaphthalene in the oxidation was 78%. -Elution
with 600 ml of methylene chloride provided an oil which vpc
analysis (above conditions) showed had two components with
retention times of 4.1 min (90%) and 8.9 min (10%). Finally,
elution with 500 ml of a 1:1 mixture of methylene chloride-
95% ethanol afforded an oil which was shown to be homogeneous
(Rt 8.9 min) by vpc (above conditions). Final purification
of all compounds was achieved by vpc. Neither of the com-

pounds was found to be thermally interconvertible under the

vpc column conditions.
1. Product Identification

a. 4-Ethyl—2,2-dimethyl-1(2H)-naphthalenone (154).

 

This oil had a R of 4.1 min and showed principal infrared

t
bands (CCl4) at 1675 (\C=O’ conjugated), 1640 (shoulder,
VC‘C) and 1600 cm-1 (VC=C' aromatic). The ultraviolet spec-

trum of iég’in 95% ethanol had maxima at 333 (log a 3.32),
283 (log a 3.42), 274 (log a 3.61), 266 (log 5 3.61) and

236 mu (log a 4.74). The nmr spectrum (CCl4) of igg'con-
sisted of a six-proton singlet at T 8.80, a threeéproton
triplet (J = 7.8 Hz) centered at T 8.80, a two-proton

quartet (J = 7.8 Hz) centered at T 7.50, a broad (hw = 3.3
cycles) one-proton singlet at T 4.25, and aromatic multiplets,

T 2.55-3.13 (33) and 2.0—2.2 (1H) .

 

121

Anal. Calcd for C14H160: C, 83.95; H, 8.05

Found: C, 83.85: H, 8.02.

b. 4—Ethyl-1,1-dimethyl-2(1H)-naphthalenone (159).

 

This oil had a Rt of 8.9 min and showed principal infrared

bands (CCl4) at 1660 (VG-0' conjugated), 1622 (VG-C' conju-
1 (v
.C:C'

spectrum of 159 in 95% ethanol had maxima at 303 (log a I

gated) and 1602 cm- aromatic). The ultraviolet

4.11), 237 (log 8 4.10) and 232 mu (log 5 4.10). The nmr
Spectrum (CC14) of 159 consisted of a three—proton triplet

(J = 7.8 Hz) centered at T 8.69, a six—proton singlet at

 

T 8.62, a two-proton quartet (J = 7.8 Hz) at T 7.29, a ‘ g
broad one-proton singlet at T 4.07, and an aromatic multi—
plet, T 2.48-2.95 (4H).

.Aggi. Calcd for C14H160: C, 83.95; H, 8.05

Found: C, 83.87; H, 8.01.

 

I. irradiation of 4-Ethyl-2,2-dimethyl-1(2H)-naphthalenone
(154) in Diethyl Ether '

 

A solution of 167 mg of 4—ethyl-2,2-dimethyl-1(2H)-
naphthalenone, 152“ in 17-ml of diethyl ether was irradiated
through a Pyrex filter with a 450-watt Hanovia Type L mer—
cury arc lamp. Monitoring the photolysis by vpc (5' x
1/4" DEGS column; 180°;100 ml/min of He) showed a progres—
sive decrease in the concentration of 122'(Rt 4.2 min) and
the appearance of two new compounds with retention times of

5.4 min and 15.5 min. The compound with R 5.4 min reached

t

a maximum concentration of 15% of the volatiles after

122

5 hours irradiation and then decreased, whereas the concen-

tration of the compound with Rt 15.5 min continued to in-

crease as the photolysis was continued. After irradiation
for 16 hours, vpc analysis of the photolysate indicated the

volatiles were composed of: 154 (30%), a compound with Rt

5.4 min (7%) and a compound with R 15.5 min (63%). The

t

compounds were purified by vpc (above conditions). -An in-

sufficient amount of the product with Rt 5.4 min was obtained

to permit identification. However, the photoproduct with

 

 

 

Rt 15.5 min has been identified as 4-ethyl-3,4-dimethyl- E
1(4H)-naphthalenone, 156. This colorless oil had major §(

bands in its ir Spectrum (CCl4) at 1660 (VC_D, conjugated),

1

1631 (v conjugated)and 1604 cm- aromatic). The

c=c' (Vc=c’
ultraviolet spectrum of 122,1n 95% ethanol had a maximum
at 252 mu (log a 4.17) and a shoulder at 269 mu (log 8 4.07).
The nmr spectrum (CCl4) of iég’consisted of a three-proton
triplet (J = 7.8 Hz) centered at T 9.62, a three-proton sing-
let at T 8.55, a two—proton quartet (J = 7.8 Hz) centered
at T 8.05, a three-proton doublet (J = 1.5 Hz) centered at
T 7.94, a broad (hw = 3.6 cycles) one-proton singlet at T
3.79 and aromatic multiplets centered at T 2.67 (3H) and
T 1.93-2.12 (1H).

Aggi. Calcd for C14H160: C, 83.95; H, 8.05

Found: C, 84.02; H, 8.09.

123

J. .Irradiation of 4-Ethyl-2,2—dimethyl-112H)-ngphthalenone

(154) in Trifluoroethanol

 

A solution of 50 mg of 152 in 5 ml of trifluoroethanol
was irradiated through a uranium glass filter (short wave-
length cut-off at about 360 mu) with a 450—watt Hanovia
Type L mercury arc lamp. Vapor phase chromatography (5' x

1/4" DEGS column; 180°; 100 ml/min of He) of the photolysis

_ “mum“

solution after 15 min irradiation showed that the photolysate

had components with the following retention times: 4.1 min,

 

154, (51%). 5.4 min (11%). and 15.3 min (38%). ~Examination
of the photolysate by vpc after irradiation for one hour L
indicated the presence of a single component with Rt 15.3

min. The photoproduct was purified by vpc and has been

identified by its infrared Spectrum and R as 4-ethyl-3,4-

t
dimethyl-1(4H)-naphthalenone, 156;
ASimilarly, irradiation of a solution of 110 mg of iii
in 11 m1 of trifluoroethanol through a Pyrex filter with a
450-watt Hanovia Type L mercury arc lamp for two hours
proceeded with complete conversion and provided a 90% yield

(nmr, hexamethylbenzene as standard) of 4-ethyl—3,4—dimethyl-

1(4H)-naphthalenone, 156.

SUMMARY

1. Irradiation of an ether solution of 1,5,6,6—tetra—

methyl-3,4-benzobicyclo[3.1.0]hexen-2-one (izg) [previously
shown to be the primary photoproduct in the irradiation of
2,2,3,4-tetramethyl-1(2H)—naphthalenone (12;)] provided an

80% yield of 2,3,4,4—tetramethyl-1(4H)-naphthalenone (124).

2. Oxidation of 1,2,4-trimethylnaphthalene with peroxy-
trifluoroacetic acid-boron fluoride etherate in methylene
chloride afforded 2,2,4-trimethyl-1(2H)-naphthalenone (122),
1,1,4-trimethyl—2(1H)-naphthalenone (£22), and an unidenti—
fied product in the ratio 81:16:3. The over-all yield

was 22%, based on 83% conversion of 1,2,4—trimethylnaphtha—

lene.
3. Irradiation of an ether solution of naphthalenone
1 6 gave 3,4,4-trimethyl-1(4H)—naphthalenone.(148). A de-

tailed cOnsideration of the possible mechanisms for the
photoisomerization of a 1(2H)—naphthalenone to a benzobi-
cyclo[3.1.0]hexenone shows that the isolation of igg'from
the photolysis of igg'requires that the photorearrangement
of naphthalenone igi’to benzobicycloketone 123 proceeds by

a "bond—crossing" mechanism.

124

 

125
4. Irradiation of a hexane solution of naphthalenone i~i
containing dimethyl amine gave benzobicycloketone 122;
Photolysis of a solution of naphthalenone 121.1“ methanol
provided naphthalenone 122,!l2 bicycloketone 123, These
results suggest that the "bond-crossing" mechanism for the

photoisomerization of a 1(2H)-naphthalenone to a benzobi-

cyclo[3.1.0]hexenone does not involve a ketene intermediate.

5. Oxidation of 4-ethyl—1,2-dimethylnaphthalene with
peroxytrifluoroacetic acid—boronfluoride etherate in
methylene chloride provided 4-ethyl-2,2-dimethyl-1(2H)-
naphthalenone (léé) and 4-ethyl—1,1-dimethyl-2(1H)—naphthar
lenone (122) in the ratio of 5:1. The over-all yield was
31%, based on 78% conversion of 4-ethyl-1,2-dimethylnaphtha-

lene.

6. Irradiation of an ether solution of naphthalenone 122'
gave 4-ethyl-3,4—dimethyl-1(4H)-naphthalenone (126). An
examination of the possible mechanisms for the photorear—
rangement of a benzobicyclo[3.1.0]hexenone to a 1(4H)—
naphthalenone shows that the isolation of naphthalenone
igg’from the irradiation of 1E2 requires that the photo—
isomerization of benzobicycloketone 122.t° naphthalenone

124 occurs via a 1,2—a1kyl migration.

 

10.

11.

12.

13.

14.

15.

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