 

'FHIE PREPARAHOR AME
?TH@T36f%EMEST&X’ OF
ﬁzﬁcﬁtAﬁeﬁTRAMETHYL-a I {QR} «MPHTHALENONE

Thesis {av the Degree 05 M. S.
MECHiGAN STATE UNIVERSETY
Roger K. Murray, .Er.

196a

 

LIBRAR y

Michigan State
nivcrsity

 

ABSTRACT
THE PREPARATION AND PHOTOCHEMISTRY OF
2,2,3,4-TETRAMETHYL-1(2H)-NAPHTHALENONE

by Roger K, Murray, Jr°

The purpose of this investigation was to study the
influence on the photochemistry of highly substituted
2,4-cyclohexadienones when one of the two carbonmcarbon
double bonds of the cyclohexadienone system belongs to a
fused aromatic ringo

The oxidation of 1,2,3,4—tetramethylnaphthalene with
peroxytrifluoroacetic acid — boron fluoride etherate in
methylene chloride at —120 gave: 2,2,3,4~tetramethyl—
1(2H)-naphthalenone (I), 1,1,3,4—tetramethyl—2(1H)—
naphthalenone (II), and 2,2,4,4—tetramethyl-1,S-dioxo—

tetralin (III) in the ratio of 61:21:180 The overall

0 O
Q «0
”\O
I II III

yield of products was 50%0 The proposed oxidation mechan-
ism readily accounts for these products.

Irradiation of naphthalenone I in ether provided 3,4-
benzo—l,5,6,6~tetramethylbicyclo[301.0]hexan-2-one (IV) as

the primary photoproducto Further irradiation of

Roger K. Murray, Jr.

naphthalenone I in ether gave a moderate yield of 2,3,4,4—

tetramethyl-l(4H)-naphthalenone (V).
0
IV V

Naphthalenone V was recovered unchanged from irradia-
tion in ether, but photolysis in methanol led to a steady
decrease in its concentration. However, no volatile products
could be detected by Vpc.

3,4—Benzo-1,5,6,6-tetramethylbicyclo[3.1.0]hexan-2~
one (IV) photolyzed rapidly in ether to afford V. Naphtha-
lenone V was also the major photoproduct when benzobicyclic-
ketone IV was irradiated in acid-free methanol, but an un-
identified product (VI) was also detected. The photochemical
relationship of VI and naphthalenone V has not yet been
established.

Irradiation of 1,1,3,4-tetramethyl—2(1H)-naphthalenone
(II) in ether or methanol led to a decrease in the concentra—
tion of naphthalenone II, but no volatile products were
detected by Vpc.

Control experiments demonstrated that none of the photo-
chemically interesting compounds studied were reactive in

the dark with the solvents in which they were irradiated.

THE PREPARATION AND PHOTOCHEMISTRY OF
2,2,3,4-TETRAMETHYL-1(2H)-NAPHTHALENONE

BY

Roger K. Murray, Jr.

A THESIS

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

MASTER OF SCIENCE
Department of Chemistry

1966

ACKNOWLEDGMENT

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

Appreciation is also due to Dr. Peter M. Collins for
many fruitful discussions and suggestions.

Appreciation is extended to Michigan State University
for a Graduate Teaching Assistantship from September, 1964
through June, 1966 and to the National Science Foundation

for financial aid during the Summer, 1966.

ii

TABLE OF CONTENTS

INTRODUCTION . . . . . . . . . . . . . . . . .

RESULTS AND DISCUSSION 0 O O O O O O O O O O O O O

A. The Oxidation of 1,2,3,4-Tetramethyl-
naphthalene . . . . . . . . . . . . . .

B. The Photochemistry of 2,2,3,4-Tetramethyl-
1(2H)-naphthalenone . . . . . . . . . .

C. The Photochemistry of 2, 3, 4 ,4-Tetramethyl-
1(4H)—naphthalenone . . . . . . . . . .

D. The Photochemistry of 3,4-Benzo-1,5,6,6-
tetramethylbicyclo[3.1.0]hexan-2-one . .

E. The Photochemistry of 1,1,3,4-Tetramethyl—
2(1H)-naphthalenone . . . . . . . . . .

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

A. General Procedures . . . . . . . . . . .

B. Preparation of 1,2,3,4-Tetramethylnaph-
thalene . . . . . . . . . . . . . . . .

1. 1—Chloromethyl-2,3-dimethyl-
naphthalene . . . . . . . . . . . .
2. 1,2,3-Trimethylnaphthalene . . . . .
3. 1-Chloromethyl-2, 3, 4—trimethyl-
naphthalene . . . . . .
4. 1, 2, 3, 4-Tetramethylnaphthalene . . .

C. The Oxidation of 1,2,3,4-Tetramethyl-
naphthalene . . . . . . . . . . . . . .

1. The Reaction with 10% Excess Oxidant
at -16° to -120 . . . . . . . . . .
a. Product Identification . . .

(1) 2, 2, 4, 4-Tetramethyl-1, 3-

dioxotetralin . . .

(2) 1, 1, 3 ,4-Tetramethyl-2(1H)-
. naphthalenone . . .

(3) 2, 2, 3 ,4-Tetramethyl-1(2H)-
naphthalenone . . . . . .

2. The Reaction with a Large Excess of
Oxidant . . . . . . . . . . . . . .

iii

Page

17

21

23

25
27
27
27
27
28
28
29
30
,30
32
32
32
33
33

TABLE OF CONTENTS (Cont.)
Page

D. The Oxidation of 2,2,3,4-Tetramethyl-
1(2H)-naphthalenone . . . . . . . . . . . 34

B. General Photolysis Procedure . . . . . . . 35

F. Irradiation of 2,2,3,4-Tetramethyl-1(2H)-
naphthalenone in Ether . . . . . . . . . . 36

G. The Dark Reaction of 2,2,3,4-Tetramethyl-
1(2H)—naphthalenone in Ether . . . . . . . 37

H. Further Irradiation of 2,2,3,4-Tetramethyl-
1(2H)-naphthalenone in Ether . . . . . . . 37

I. A Comparison of the Rate of Photolysis of
2,3,4,5,6,6-Hexamethylcyclohexa-2,4—di-
enone in Ether and 2,2,3,4-Tetramethyl—
1(2H)-naphthalenone in Ether and Methanol. 39

J. Irradiation of 3,4—Benzo—1,5,6,6—tetramethyl-
bicyclo[B.1.0]hexan-2-one in Ether . . . . 89

K. The Dark Reaction of 3,4-Benzo-1,5,6,6-
tetramethylbicyclo[3.1.0]hexan-2-one in
Ether . . . . . . . . . . . . . . . . . . 40

L. Irradiation of 3,4-Benzo-1,5,6,6-tetramethyl-
bicyclo[3.1.0]hexan-2-one in Methanol. . . 40

M. Irradiation of 2,3,4,4-Tetramethyl-1(4H)-
naphthalenone in Ether_.7. . . . . . . . . 41

N. Irradiation of 2,3,4,4-Tetramethyl-1(4H)-
naphthalenone in Methanol . . . . . . . . 42

O. Irradiation of 1,1,3,4-Tetramethyl-2(1H)-
naphthalenone in Ether through Pyrex . . . 42

P. Irradiation of 1,1,3,4-Tetramethyl-2(1H)-
naphthalenone in Methanol through Quartz . 43

Q. The reaction of 1,1,3,4-Tetramethyl-2(1H)-
naphthalenone with Methylmagnesium Iodide. 43

SUMMARY . . . . . . . . . . . . . . . . . . . . . . 45

LITERATURE CITED . . . . . . . . . . . . . . . . . . 47

iv

TABLE OF CONTENTS (Cont.)

APPENDIX

1.

2.

NMR Spectrum of 2,2,4,4-Tetramethyl-1,3-
dioxotetralin . . . . . . . . . . . .

NMR Spectrum of 1,1,3,4-Tetramethyl-2(1H)-

naphthalenone . . . . . . . . . . ...

NMR Spectrum of 2,2,3,4-Tetramethy1-1(2H)-

naphthalenone . . . . . . . . . . ...

NMR Spectrum of 3,4—Benzo-1,5,6,6-tetra-
methylbicyclo[3.1.0]hexan-2-one . . .

NMR Spectrum of 2, 3, 4, 4-Tetramethyl—1(4H)-
naphthalenone . . . . . . . . . . . .

Page

50

51

52

53

54

55

LIST OF FIGURES

Figure Page
1. Possible courses for the photochemical
reaction of 2,4—cyclohexadienones having
blocked ortho-positions . . . . . . . . . 4

2. A mechanism for the formation of the oxidation
products of 1,2,3,4-tetramethylnaphthalene. 14

vi

INTRODUCTION

Organic peracids have long been recognized as sources
of electrophilic (positive) hydroxyl useful for the oxida—
tion of certain aromatic hydrocarbons (1). An especially
good source of positive hydroxyl has been peroxytrifluoro-
acetic acid, as the trifluoroacetate ion is a good leaving
group (2). However, the use of this peracid in oxidations
often led to low conversions. It was proposed (3) that a
Lewis acid might facilitate the decomposition of peroxy-
trifluoroacetic acid under mild conditions through coordina-
tion with one of the oxygens not used ultimately as an

oxidant.

O BF3 O

CF3-C or CF3-C
‘VUEOH \O-OH

BF?!

The use of peroxytrifluoroacetic acid in the presence

-——> CF3C02_ + OH+

of boron fluoride proved effective in the hydroxylation of
certain aromatic hydrocarbons. The yield of phenol was
especially good if positions 23322 or para to the entering
hydroxyl group were blocked to retard further oxidation.
Thus mesitylene, I, was converted to mesitol, II, in good
yield with efficient use of the peracid even at -409, and

isodurene was converted to isodurenol in 65% yield (4).

OH

CF3C03H-BF3
-40°, > 90% ’

 

I II

When the oxidation was applied to prehnitene, III, (4)
several products were obtained in addition to the expected
prehnitol.

Although obtained in very low yield, the isolation of

4,5,6,6-tetramethyl-2,4-cyclohexadienone, IV, in this re-

other

 

V

products

III IV

action was especially interesting. The product was ac—
counted for by attack of the electrophilic oxidant at C-1
of the hydrocarbon, followed by a Wagner-Meerwein methyl
migration and loss of a proton. The supposition, that if
the original hydrocarbon were entirely alkylated the dom-
inant reaction path would be conversion to dienone, was
realized in the peroxytrifluoroacetic acid-boron fluoride
oxidation of hexamethylbenzene to hexamethyl-2,4-cyclo-

hexadienone, V, (5). The major products from the oxidation

0

3
of pentamethylbenzene are also dienones (6); even the oxida-
tion of durene proceeded to give over 50% of dienone VI (7).

The photochemistry of 2,4-cyclohexadienones has gen?
erated considerable attention (8,9,10). Barton and Quinkert
elucidated three types of photochemical transformations of
2,4-cyclohexadienones having blocked ortho-positions (11):
(a) ring fission to a gigfdiene ketene; (b) acetoxyl group
migration from C-6 to C-5, if unsubstituted, with con-
comitant aromatization to a phenol; and (c) expulsion of
an acetoxyl group from C-6, followed by aromatization to
a phenol. These alternatives are depicted in Figure 1.

The most important rearrangement process is ring fission
of a 2,4-cyclohexadienone, A, to afford a Sigfdiene ketene,
B, followed by isomerization to the trans-diene.ketene, C,
which can then react with an available nucleophile, D, to
provide the observed product, E or F. The ease with which
this reaction proceeds depends on the number and positions
of the substituents in the cyclohexadienone molecule, and
on the nucleophilic character of H-X.

If the substituents of the intermediate diene ketene
do not cause mutual steric hindrance, then a weakly nucleo-
philic reactant H-X is sufficient to lead to products via
C. Thus the irradiation of 6-acetoxy-6-methy1-2,4-cyclo-
hexadienone (A; R2 3 OAc, R' = Me, R3 = R4 = H) in ether
containing water gives the corresponding unsaturated acid
(E; R2 = OAc, R' = Me, R3 - R4 = H). However, if mutual

repulsions exist so that the desired trans-diene ketene has

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unfavorable interactions between the substituents, then the
trans-form, C, is destabilized relative to the gigfdiene
ketene, B, and the rate of the back reaction to give the
cyclohexadienone, A, is increased. In this case the
formation of the acid derivatives will only predominate if
a strong nucleophile (e.g., a primary amine) is used.

Recyclization of the gisfdiene ketene permits slower
processes to become important, namely the formation of
phenols, either by a dienone/phenol photo—rearrangement to
give G, or by homolytic photo—dissociation followed by
abstraction of hydrogen from the solvent to give H. The
dienone/phenol photo-rearrangement requires R2 to be a
nucleophilic group. Thus irradiation of 2,4,6-trimethyl-6—
acetoxy-2,4-cyclohexadienone (A; R2 = OAc, R‘ = R3 = R4 = Me)
in dry ether, or in the presence of water or aniline gave‘
3-acetoxy mesitol (G; R2 = OAC, R1 = R3 = R4 = Me), whereas
the analogous compound (A; R2 = allyl, R1 = R3 = R4 = Me)
did not undergo such a rearrangement. The migration of the
acetoxyl group to an adjacent carbon is a typical example
of neighboring group participation. EXpulsion of an acetoxyl
group from C-6, followed by aromatization to a phenol, is
demonstrated in the irradiation 0f 6—acetoxy-6-methy1-2,4—
cyclohexadienone (A; R2 = OAc, R1 = Me, R3 = R4 = H) in
anhydrous ether to give gfcresol (H; Ri = Me, R3 = R4 = H).

A novel photochemical path has recently been discovered

for highly substituted 2,4-cyclohexadienones. Irradiation

6
of a 1% ether solution of hexamethyl-2,4—cyclohexadienone,
V, (12) or hexaethyl-Z,4-cyclohexadienone, VII, (5) in
Pyrex produced photo-rearrangement to the corresponding

bicyclo[3.1.0]hexane derivatives, VIII and IX. Labeling

R O

R H R R

R hv > R
R R R

R R
R
V R = CH3 VIII R = CH3
VII R = CH2CH3 IX R = CH2CH3

experiments established that the product was formed by a
"bond-crossing" rather than an alkyl migration mechanism.
It was suggested that the trans-diene ketene that would
result from V would have an unfavored structure due to
the 1,3-methyl interactions present and that conversion to
a bicyclic enone would thus be a more favorable energetic
process. The authors further stated that some 2,4-cyclo—
hexadienones that appear to give diene-ketenes by a pre—
ferred route may do so only because the bicyclic enones
initially formed are photochemically reconverted to starting
material.

In order to study further the structural requirements
for this photo-rearrangement, it was desired to irradiate
the benzo-derivatives of hexamethyl-Z,4-cyclohexadienone, V,

namely tetramethylnaphthalenones X and XI. It was

X XI

anticipated that having one of the two C=C bonds of the
cyclohexadienone system belong to a fused aromatic ring
might well effect the course of the photochemical reaction.
It was proposed that synthesis of the desired un-
known naphthalenones X and XI could be achieved by peroxy-
trifluoroacetic acid-boron fluoride oxidation of 1,2,3,4—
tetramethylnaphthalene, XII. Attack of electrophilic

(positive) hydroxyl at an a-methyl-bearing carbon, followed

B\5XI

XII

by a Wagner-Meerwein methyl migration to C-2 and loss of
a proton, might well afford naphthalenone X. Similarly,
attack of positive hydroxyl at a B-methyl-bearing carbon,
followed by a methyl migration to C-1 and loss of a pro-
ton might provide naphthalenone XI.

The synthesis and photochemistry of tetramethyl-

naphthalenones X and XI is the subject of this thesis.

RESULTS AND DISCUSS ION
A. The Oxidation of 1,2,3,4-Tetramethylnaphthalene

1,2,3,4-Tetramethylnaphthalene was prepared via a
modification of the method of Hewett (13), although several
other syntheses of the compound have been reported (14—17).
2,3-Dimethylnaphthalene was added to a solution of para-
formaldehyde in acetic acid through which hydrogen chloride
gas had been passed. Hydrogenolysis of the resulting
1-chloromethyl-2,3-dimethylnaphthalene by reaction with a
suspension of lithium aluminum hydride in tetrahydrofuran
provided 1,2,3-trimethylnaphthalene. Repetition of the
chloromethylation and hydroryanolysis afforded a moderate
yield of 1,2,3,4-tetramethylnaphthalene.

1,2,3,4-Tetramethylnaphthalene was oxidized at -160
to -120 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 the tetramethylnaphthalene.
The volatile products were separated by distillation and

"purified by Vpc° The composition of the volatile material
was determined by Vpc and is calculated on an 83% conversion
of tetramethylnaphthalene. The products were assigned the
following structures, based on evidence which will be
presented:

2,2,3,4-tetramethyl—1(2H)-naphthalenone (X) 61%,

8

9
1,1,3,4-tetramethyl-2(1H)-naphthalenone (XI) 21%,

2,2,4,4-tetramethyl-1,3-dioxotetralin (XIII) 18%.

CF3C03H

 

('37

XI XIII

Compound XIII analyzed well for the formula C14H1602.
The mass spectrum indicated a parent peak at m/e 216 show-
ing this to be the molecular formula. The infrared spectrum
of XIII had carbonyl absorptions at 1712 and 1683 cm"1
(liquid film) and only aromatic C=C stretching vibrations,
while the uv spectrum had maxima at 289 mu (log a 3.12) and
248 mu (log 8 3.83) in 95% ethanol. The nmr spectrum of
XIII consisted of six-proton singlets at T 8.67 and 8.52
(ggmrdimethyl groups) and a complex multiplet for four pro-
tons at T 2.63 (aromatic protons).

These data suggested a tetramethyldioxotetralin of
which there are four isomers, XIII - XVI. The 1,4- and
2,3-dioxoisomers XV and XVI were eliminated as rapid flipping

of the non-aromatic ring would make the ggmfdimethyl groups

10

XIV' XV XVI

equivalent in each compound leading to a single peak in
the nmr spectrum. The 1,2-dioxoisomer XIV was ruled out
as a-diketones typically show ir carbonyl absorptions at
1730-1725 cm_1 (18) and ultraviolet maxima at longer wave-
lengths than B—diketones (19). For example, in XVII the

absorption maximum is at 380 mu (19) and in benzil, XVIII,

at 370 mu (20).

A: v.

XVII XVIII

The six-proton singlets in the nmr spectrum at T
8.67 and 8.52 are assigned to the ggmfdimethyl groups at
C-3 and C-1 respectively. These assignments are consistent
as the ggmfdimethyl groups in 2,2,4,4-tetramethyl—1,3-
dioxocyclobutane, XIX, appear at 8.691 (21) and the gem:
dimethyl group at C—1 in 1,1,4,4-tetramethyl-2-oxotetralin,

XX, appears at 8.561 (22).

11

 

XIX XX

Compound XIII is believed to be the first isolated
1,3-dioxotetralin. The only other 1,3-dioxotetralin re—

ported is 4,4-dimethyl-1,3-dioxotetralin, XXI (23). How—

0 O
lillul
OH

XXI XXII

 

ever diketone XXI seemed to be nearly completely enolic
in character and is better represented by the tautomeric
structure XXII.

Compound XI analyzed well for the formula C14H160 and
a parent peak at m/e 200 in the mass spectrum indicated
this to be the molecular formula. Compound XI was an oil
with AﬁEﬁH 308 mu (log 5 3.91), 239 mu (log a 3.95)
and 234 mu (log a 3.97). The ir spectrum of XI showed
conjugated carbonyl and double bond absorptions at 1652 and
1621 cm.1 (liquid film), respectively. The nmr spectrum

of XI had a six-proton singlet at T 8.60 (ggmrdimethyl

group), two three-proton singlets at T 8.00 and 7.68

12

(allylic methyls) and a complex multiplet for four aromatic
protons centered at T 2.76. The allylic methyls at T 8.00
and 7.68 are tentatively assigned to the methyls at C-3
and C-4 respectively, as a methyl attached to the B carbon
of a cyclic dienone exhibits a lower field signal (5,24).

This Spectroscopic evidence compares favorably with
similar data obtained for the known compound 1,1-dimethyl-

2(1H)-naphthalenone, XXIII. Cromwell and Campbell (23)

/O

XXIII

have reported ultraviolet absorption maxima for naphthalenone
XXIII at 300 mu (log 8 4.00), 294 mu (log a 4.00), 236 mu
(log 5 4.20) and 230 mu (log 8 4.19), while Baddeley and
Rasburn (24) have reported absorption maxima in ethanol

at 310 mu (loge:3.75) and 230 mu (log a 4.38) for the same
compound. The ir spectrum of XXIII showed carbonyl ab-
sorption at 1658 (nujol) or 1662 cm'1(CC14) (25) and c=c
absorption at 1624 cm-1(23).

The major product of the oxidation was 2,2,3,4—tetra—
methyl-2(1H)—naphthalenone, X. Compound X was a colorless
oil and had a molecular formula of C14H130, as indicated
by its elemental analysis and a parent peak at m/e 200 in
the mass spectrum. The ir spectrum of X had conjugated

-1
carbonyl and double bond absorptions at 1674 and 1633 cm

13

(liquid film) respectively. The uv spectrum consisted of:

kEtOH

max
(log a 3.49), 268 mu (log 5 3.49) and 239 mu (log a 5.05).

340 mu (log a 3.14), 286 mu (log a 3.33), 276 mu

The nmr spectrum of X contained a six-proton singlet at T
8.75 (géﬂrdimethyl group), two three-proton singlets at T
8.05 and 7.90 (allylic methyls) and a complex multiplet
equivalent to four protons at T 2.63 (aromatic protons).
The postulated mechanism for the formation of the
oxidation products is depicted in Figure 2. For simplicity
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 (27).
Strong evidence has been presented by Norman and Davidson
supporting the intermediacy of an electrophilic, cationic
reactant in peroxytrifluoroacetic acid oxidations (28).
Naphthalenone X is presumably formed by electrophilic
attack of peroxytrifluoroacetic acid at an a-methyl-bearing
carbon of 1,2,3,4-tetramethylnaphthalene, leading to the
intermediate carbonium ion XXIV. Wagner-Meerwein migra-
tion of a methyl group to C-2 would provide carbonium ion
XXV and loss of a proton would give naphthalenone X. Simi—
larly, the formation of naphthalenone XI is accounted for
by attack of the electrOphilic oxidant at a B-methyl-bear—
ing carbon of the tetramethylnaphthalene, leading to car-
bonium ion XXVI. .Migration of a methyl group to C-1 would
afford intermediate carbonium ion XXVII and loss of a proton

would give naphthalenone XI.

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15
A less likely alternative for the carbonium ion re-
sulting from attack at a B-methyl-bearing carbon (XXX) would

be methyl migration in the other direction and proton loss

0H -H+ o
OH ~CHq '5

XXX XXI XXXII

to provide XXXII. However, this process would involve
disruption of the aromatic ring. The loss of aromatic
resonance energy required for the formation of XXXII may
well explain why this product was not observed.

The over-oxidation product 2,2,4,4-tetramethyl-1,3—
dioxotetralin, XIII, is accounted for by further oxida—
tion of 2,2,3,4-tetramethyl-1(2H)-naphthalenone, X.
Attack of the electrophilic oxidant at C-3 of naphthalen-
one X would provide the well stabilized benzylic carbonium
ion XXVIII. Wagner-Meerwein migration of a methyl group
to C-4 would give carbonium ion XXIX and loss of a proton
would afford XIII. In order to support this mechanism,
2,2,3,4-tetramethyl-1(2H)-naphthalenone was oxidized with
peroxytrifluoroacetic acid—boron fluoride etherate in
methylene chloride at —15°. Vpc analysis of the volatile
products indicated only a trace of starting naphthalenone
present and almost complete conversion to 2,2,4,4-tetra-

methyl-1,3-dioxotetralin.

16
It does not seem that the dioxotetralin XIII is formed
from naphthalenone XI. The required intermediate carbonium

ion XXXIII would be destabilized by a positive charge on a

HO
XXXIII

carbon atom O’to a carbonyl. When 1,2,3,4-tetramethyl-
naphthalene was oxidized with a large excess of peroxy-
trifluoroacetic acid-boron fluoride etherate in methylene
chloride at -10°, no 2,2,3,4-tetramethyl-1(2H)-naphthalen-
one was detected in Vpc analysis of the isolated products.
The two major components of the isolated volatile material
were 2,2,4,4—tetramethyl—1,3-dioxotetralin (40%) and
1,1,3,4-tetramethyl-2(1H)-naphthalenone (54%).

Vpc analysis of the products from the equimolar oxi-
dation of 1,2,3,4—tetramethy1naphthalene indicates a prefer—
ence for attack at an a-methyl-bearing carbon over attack
at a B-methyl-bearing carbon of 4:1. Two factors may
contribute to this preference of attack. .First, the inter-
mediate carbonium ion XXIV is better stabilized than car—
bonium ion XXVI. Second, an a-methyl-bearing carbon is
flanked by only one methyl group, whereas a B-methyl-bearing
carbon is flanked by two methyls, thus a steric approach

factor may be involved.

17

B. The Photochemistry_of 2,2,3,4-Tetramethyl-112H):

naphthalenone

Four types of photochemical transformations of 2,4—
cyclohexadienones having blocked ortho—positions have been
reported (see Introduction). Which photochemical process
occurs seems to depend largely on the number and positions
of the substituents in the cyclohexadienone molecule and
on the nucleophilic character of the solvent (5,6,7,11).
Most 2,4-cyclohexadienones studied undergo ring fission
on photolysis in Pyrex to give a diene-ketene which is
then attacked by a nucleophile present in the solvent to
provide the observed product. However, highly substituted
dienones, such as hexamethyl-2,4-cyclohexadienone, were
recently shown to photochemically rearrange to the correrr
sponding bicyclo[3.1.0]hexane derivatives (5,6,12).
2,2,3,4-Tetramethyl-1(2H)-naphthalenone offered a probe to
study the photochemical rearrangement when one of the two
c=c bonds of the cyclohexadienone system belongs to a fused
aromatic ring.

Irradiation of an approximately 1.5% solution of naph—
thalenone X in anhydrous ether with a Hanovia L 450—w lamp
was carried out in Pyrex. The reaction was monitored using
Vpc. Irradiation led to a decrease in the concentration of
naphthalenone X and an increase in the concentration of
a photoproduct which reached a maximum concentration after

photolysis for two hours. The primary photoproduct was

18
shown to be 3,4-benzo-1,5,6,6-tetramethylbicyclo[3.1.0]-

hexan-2-one, XXXIV.

 

%

O
hv,Pyrex
Etzo >

X XXXIV

The benzobicyclicketone XXXIV was shown to be iso—
meric with naphthalenone X by its elemental analysis and
a parent peak at m/e 200 in the mass spectrum. The infra-
red Spectrum had carbonyl absorption at 1699 cm.1 and
only aromatic c=c stretching vibrations. The ultraviolet
spectrum had maxima at: 335 mu (log a 2.69), 313 mu (log 5
3.20), 301 mu (log 8 3.29), 247 mu (log a 4.05) and 225 mu
(log 5 4.42). The nmr spectrum of XXXIV consisted of
three-proton singlets at T 9.28, 8.84, 8.73 and 8.49 (ali-
phatic methyls) and a complex multiplet equivalent to four
protons at T 2.6 (aromatic protons). The two aliphatic
methyls at highest field are tentatively assigned as the
ggmfdimethyl group, while the methyls at T 8.73 and 8.49
are assigned as the bridgehead methyls at C-1 and C-5 re—
spectively.

The photo-rearrangement of naphthalenone X was found
to proceed one-half as fast as the corresponding photo-

isomerization of hexamethyl-2,4-cyclohexadienone V under

19
the same conditions. A 2.5 fold rate enhancement was ob-
served when the photolysis of naphthalenone X was carried
out in methanol rather than ether.

A tenable mechanism for the photochemical isomeriza—
tion of 2,2,3,4-tetramethyl—1(2H)—naphthalenone to 3,4-benzo-
1,5,6,6-tetramethylbicyclo[3.1.0]hexan-2-one is presented
below. Ionic intermediates are used in the mechanism only
for convenience. This "bond-crossing" mechanism is analo-
gous to the mechanism that was established by labeling exe
periments for the photochemical rearrangement of hexa-

methyl-2,4-cyclohexadienone V to hexamethylbicyCIo[3.1.0]hex-

3-en-2-one, VIII (5,12).
0 O

‘I

 

?
Q» <—-—— \

XXXIV

Further irradiation of the anhydrous ether solution
of naphthalenone X lEd to a substantial decrease in the con-
centration of the initial phot0product XXXIV and an increase

in the concentration of a new product. This product was

20
shown to be 2,3,4,4-tetramethyl-1(4H)-naphthalenone, XXXV.

Elemental analysis of XXXV indicated an empirical formula

0 ‘f

XXXV XXXVI

isomeric with naphthalenone X and benzobicyclicketone XXXIV.
Naphthalenone XXXV had absorption maxima at 272 mu (log a
4.03) and 256 mu (log 5 4.06). The ir spectrum of XXXV
showed conjugated carbonyl and double bond absorptions at
1648 and 1626 cm.1 (CCl4) respectively. The nmr spectrum
had a six-proton singlet at T 8.52 (géﬂfdimethyl group),
two three-proton singlets at T 8.02 and 7.93 (allylic
methyls) and a complex multiplet for four protons at T 2.57
(aromatic protons). The allylic methyls at T 8.02 and 7.93
are tentatively assigned to the methyls at C-2 and C-3
respectively (5,24).

This Spectroscopic evidence compares well with similar
data obtained for the closely related compound 3,4,4-tri-
methyl-1(4H)-naphthalenone, XXXVI. Huffman and Bethea (29)
have reported ultraviolet absorption maxima for naphtha-
lenone XXXVI at 271 mu (log 5 3.99) and 252 mu (log a 4.09)

and an infrared carbonyl absorption at 6.02 u (1661 cm-1)

21

C. The Photochemistry of 2,3,4,4-Tetramethyl-1(4H):
naphthalenone

Two primary photochemical transformations of 2,5—cyclo-
hexadienones have been described: (a) rearrangement to the
corresponding bicyclo[3.1.0]hexane derivative, and (b) ex-
pulsion of a substituent from C-4, followed by aromatiza-
tion to a phenol.

For example, irradiation of 4,4-diphenyl-cyclohexa-
dienone XXXVII in aqueous dioxane with light of wavelength

above 310 mu afforded bicyclic ketone XXXVIII (30,31).

hv -
aq. dioxane)

 

C6H5
H5C6 C6H5

XXXVII XXXVIII

The alternative path was demonstrated recently in the
photolysis of spiro[2.5]octa-4,7-dien-6-one, XXXIX; in
ether which gave predominantly prethylphenol, XL, and

three other compounds which were 1:1 adducts of starting

C) 011

other
hv + products
Et20

A.) CszCTTg

XXXIX XL

22
material and solvent (32). That the radical fragmentation
route competes directly with the route to "lumiproduct"
was shown by the irradiation of dienone XLI in a variety
of solvents to give a mixture of pﬁcresol,.XLII, and

bicyclicketone XLIII (33).

 

OH
———.. h” '> +
CH3 CCl3 CH3
AXLI XLII XLIII

As expected, irradiation of hexamethyl-2,5-cyclohexa-

dienone, XLIV, in ether or methanol gave bicyclicketone VIII

f’
Tit—Luis

XLIV VIII

(34).

When the benzo-derivative of dienone XLIV, namely
2,3,4,4-tetramethyl-1(4H)-naphthalenone, XXXV, was irradi-
ated in ether through a Vycor filter with a Hanovia S 200-w
lamp for 4 1/2 hours, no dimunition in the concentration
of naphthalenone XXXV was Observed and the starting material

was recovered unchanged.

23
Irradiation of an acid-free methanolic solution of
naphthalenone XXXV through a Vycor filter with a Hanovia
S 200-w lamp led to a steady decrease in the concentration
of starting material. However, no volatile material could

be detected by vpc analysis.

D. The Photochemistry of 3,4-Benzo-1,5,6,6-tetramethyl—
bicyclo[B.1.0]hexan-2-one

Irradiations of bicyclo[3.1.0]hexenones have been
shown to lead to 2,4-cyclohexadienones or to aromatic
products. For example, irradiation of bicyclicketone XLV
in methanol gave dienone XLVI as the only isolated product

(24). The alternative photochemical path is demonstrated

// {Ill hv >
CH3OH .

XLV XLVI

 

by the irradiation of umbellulone, XLVII, which quanti-

tatively provided thymol, XLVIII (35).

\ .

 

v

XLVII XLVIII

24
Very recently it has been shown that irradiation of
an acid-free methanolic solution of hexamethylbicyclic-
ketone VIII gave as the direct photOproduct compound XLIX,

which rearranged to dienone XLIV on treatment with dilute

 

HCl (34).
O CH3O OH
+
_> hv , Pyr ex; H
CH3OH
VIII . XLIX XLIV

Irradiation of 3,4-benzo-1,5,6,6-tetramethylbicyclo-
[3.1.0]hexan-2-one, XXXIV, in anhydrous ether through Pyrex
with a Hanovia15450-w lamp led to a smooth, efficient con-
version to 2,3,4,4-tetramethyl-1(4H)-naphthalenone, XXXV.
When the irradiation was carried out with an acid-free
methanolic solution of benzobicyclicketone XXXIV, the
major product isolated was again naphthalenone XXXV. How—

ever, another product from the photolysis, L, was also

a
hv,Pyrex
> +
" CH3 OH L

 

XXXIV XXXV

observed. When the reaction was monitored by uv spectroscopy,

25

a decrease in the benzobicyclicketone absorption at 301 mu
was immediately observed, and new maxima appeared at 276
and 254 mu, typical of naphthalenone XXXV. Monitoring the
photolysis by Vpc showed that the relative ratio of con-
centrations of XXXV to L remained nearly constant during
the irradiation, although the concentrations of XXXV and
L each increased at the expense of the starting ketone
XXXIV. It was shown that L did not rearrange under the
vpc conditions to give XXXV.

From these observations it can not be asserted whether
naphthalenone XXXV is or is not a direct photoproduct of
XXXIV. The hientity and photochemistry of L is obviously

of critical importance in establishing whether L is an

intermediate in the photochemical rearrangement.

E. The Photochemistry of 1,1,3,4-Tetramethyl-2(1H)e

naphthalenone

 

There are two benzo-derivatives of hexamethyl-2,4-
cyclohexadienone V, namely naphthalenones X and XI. The
photochemistry of 2,2,3,4-tetramethyl-1(2H)-naphthalenone,
X, has already been discussed.

Irradiation of a solution of 1,1,3,4-tetramethyl-2(1H)-
naphthalenone, XI, in anhydrous ether with a Hanovia L
450-w lamp was carried out in Pyrex. After irradiation
for 3 1/2 hours a slight decrease in the concentration of
starting material was observed, but no volatile material

could be detected by Vpc analysis. Similar results were

26

observed when a methanolic solution of naphthalenone XI
was irradiated for 2 hours through quartz with a Hanovia
L 450—w lamp.

These results parallel those described by Quinkert
in a preliminary report (10). Even in the presence of
cyclohexylamine, no amide could be isolated from the
photolysis of 1,1-dimethyl-2(1H)-naphthalenone, XXIII.
Irradiation of 1-acetoxy-1-methyl-2(1H)-naphthalenone in
ether saturated with water led to a mixture of dimers, the
substrate simply behaving like an a,B-unsaturated ketone.
That the fused ring must be aromatic in order to produce

such results was demonstrated by the photolysis of LI.

OAC CH3
40
hv > OAc
aq. Et 0 .
OH
LI LII

Irradiation of LI in aqueous ether gave LII as the main
product accompanied by a mixture of phenols. The stereo-

chemistry of LII has not been determined.

EXPERIMENTAL
A. General Procedures

All ultraviolet spectra were measured with a Unicam
Model SP-800 or a Beckman Model DB spectrophotometer. The
infrared spectra were obtained on a Unicam Model SP-200
infrared spectrometer and all ir spectra were calibrated
(polystyrene). All nmr spectra were measured with a
Varian A-60 spectrometer using tetramethylsilane as an
internal reference. The mass spectra were carried out
by Mr. H. Harris of this laboratory with a Consolidated
Electrodynamic Corp. 21-103C instrument operating at an
ionizing potential of 70 v. Elemental analyses are by
Spang Microanalytical Laboratories, Ann Arbor, Michigan.

Melting points are uncorrected.
B. Preparation of 1,2,3,4—Tetramethylnaphthalene(13)
1. 1-Chloromethyl-2,3—dimethylnaphthalene (13)

2,3—Dimethylnaphthalene (40.0 g, 0.256 mole) was
added to a solution of paraformaldehyde (20.4 g) in 250 m1
of acetic acid through which hydrogen chloride gas had been
passed to give a clear solution. The suspension was stir—
red vigorously at room temperature for 21 hours and then
left at room temperature for an additional 18 hrs. The
resulting solution was diluted with water (200 ml) and
extracted with benzene (3 x 100 ml). The benzene extract

27

28
was washed with dilute sodium carbonate solution and then
dried over anhydrous magnesium sulfate. After removal of
the solvent on a rotary evaporator, the residue was distilled,
bp 121-1230 (0.1 mm), providing 34.6 g (0.17 mole) of
1-chloromethyl-2,3—dimethylnaphthalene, mp 84-870 (lit.

val. (13) 86-870). The yield was 66.3%.
2. 1,2,3-Trimethylnaphthalene (13)

A solution of 34.6 g (0.17 mole) of 1-chloromethyl-
2,3-dimethylnaphthalene in 200 ml of dry tetrahydrofuran
was added over 2.5 hours to a suspension of 3.8 g (0.1 mole)
of lithium aluminum hydride in 170 ml of dry, vigorously
stirred, refluxing tetrahydrofuran. The mixture was stir—
red at reflux for an additional 3 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 75 ml of 10% HCl and 75 ml of water. The resulting
mixture was extracted with ether (3 x 150 ml) and the
separated ether layer was dried over anhydrous magnesium
sulfate. The ether solution was evaporated to an oil which
was distilled, bp 119-1220 (2 mm) and provided 23.6 g
(0.139 mole) of 1,2,3-trimethylnaphthalene, mp 25—270

(lit. val. (13) 27-280). The yield was 81.8%.
3. 1-Chloromethyl-2,3,4-trimethylnaphthalene (13)

To 11.2 g of paraformaldehyde in 140 ml of acetic acid

through which hydrogen chloride gas had been passed to give

29
a clear solution was added 23.6 g (0.139 mole) of 1,2,3-
trimethylnaphthalene. After 22 hrs of vigorous stirring,
during which the solid chloromethyl compound separated,
the solution was diluted with water and extracted with
benzene. The benzene extract was washed with dilute sodium
carbonate solution and then dried over anhydrous magnesium
sulfate. After removing the solvent the residue was
19.2 g (0.088 mole) of 1-chloromethyl-2,3,4—trimethyl-
naphthalene, mp 92—960 (lit. val. (13) 94-950). The yield

was 63.5%.
4. 1,2,3,4-Tetramethylnaphthalene (13)

1-Chloromethyl-2,3,4—trimethylnaphthalene (19.2 g,
0.088 mole) in dry tetrahydrofuran (150 ml) was added over
1.5 hrs to a suspension of lithium aluminum hydride (4 g,
0.121 mole) in 150 ml of dry, vigorously stirred, reflux-
ing tetrahydrofuran. The mixture was stirred at reflux for
an additional 3 hrs. After cooling, water was added and
the mixture extracted with ether (3 x 100 ml). The organic
extract was dried over anhydrous magnesium sulfate and the
solvent evaporated. The residue was recrystallized twice
from 95% ethanol and provided 13.5 g (0.073 mole) of
1,2,3,4-tetramethylnaphthalene, mp 104—1060 (lit. val. (13)
106.5-107.5°). The yield from 2,3-dimethylnaphthalene is
28.6%. The uv and nmr values of 1,2,3,4-tetramethyl-

naphthalene correspond exactly to those of the literature:

95%EtOH (

max 322)’ 293' and (282) mu (Ref. 36). The nmr

A

30
spectrum (CCl4 soln) contained singlets at T 7.62 (6H; 6
methyls), T 7.43 (6H; a methyls) and two multiplets centered

at T 2.72 (2H) and T 2.10 (2H) (Ref. 37).
C. The Oxidation of 1,2,3,4-Tetramethylnaphthalene
1. The Reaction with 10% Excess Oxidant at -16 to —12°.

A solution of peroxytrifluoroacetic acid (38) prepared
from 0.725 ml of 90% hydrogen peroxide (0.0268 mole) and
6.2 g (0.0295 mole) of trifluoroacetic anhydride in 10 ml
of freshly distilled methylene chloride, was cooled to -180
and added with stirring over 80 min to a solution of 4.5 g
(0.0244 mole) of 1,2,3,4-tetramethylnaphthalene in 50 ml
of methylene chloride which had previously been cooled via
a carbon tetrachloride-dry ice bath to -18°. Boron trifluor—
ide etherate (8.1 ml of 47% BF3-Et20, 0.0268 mole) was
added concurrently with the addition of the peracid. The
temperature of the solution was maintained between -160
and -120 throughout the addition. After further stirring
for 90 min at -18°, 50 ml of water was added and the
organic layer was separated. The organic layer was washed
with water (3 x 75 ml), saturated sodium bicarbonate (3 x
100 ml), extracted with 10% aqueous sodium hydroxide (4 x
100 ml), and washed with water (3 x 100 ml). The aqueous
sodium hydroxide extract and the methylene chloride fraction

were investigated separately.

31

The aqueous base fraction was acidified with dilute
hydrochloric acid and again extracted with methylene chlor-
ide (3 x 50 ml), which yielded on evaporation 0.06 g of
a dark viscous oil. Vapor phase chromatography (20' x 1/4"
SE-30 column, 220°, flow rate 90 ml/min of helium) in-
dicated seven components. This material was not further
investigated.

The methylene chloride fraction was dried over anhydrous
magnesium sulfate and evaporated to afford a deep red viscous
oil. This material was vacuum distilled at 0.05 mm to
afford 3.19 g of a yellow liquid, bp 88-900. The pot
residue was 0.97 g of deep red very viscous material.

Vapor phase chromatography (20' x 1/4" SE—30 column, 230°,
flow rate 60 ml/min of helium) showed that the crude oil
had components with the following retention times: 18.0
min (13.6%), 23.1 min (15.7%), 24.5 min (47.2%), 33.6 min
(23.4%). The compound of longest retention time was
identified by its mp (105-1060), uv spectrum, and reten-
tion time as 1,2,3,4-tetramethylnaphthalene. Conversion
of tetramethylnaphthalene was 83.3%. Final purification
of all compounds was achieved by vpc. The purity of the
compounds was checked by Vpc on two different stationary
phases and alwaysfound to be at least 98% homogeneous.
None of the compounds were found to be thermally inter-

convertible under the vpc column conditions.

32

a. Product Identification

(1) 2,2,4,4-Tetramethyl-1,3—dioxotetralin. This
was the compound with a retention time of 18.0 min. It

was a yellow oil with A95%EtOH 289

max mu (log 5 3.12) and

248 mu (log 5 3.83). Its ir spectrum (liquid film)
showed principal bands at 1712 and 1683 (VC=O) and 1600 cm"-1
(VC=C’ aromatic). The mass spectrum indicated a parent
peak at m/e 216. The nmr spectrum (CCl4 soln) consisted
of sharp singlets at T 8.67 (6H) and T 8.52 (6H) due to
the ggmfdimethyl groups at C-3 and C-1 respectively, and ~
a complex multiplet centered at T 2.63 (4H; aromatic
protons).

Anal. Calcd for C14H1602: C, 77.77; H, 7.41.

Found: C, 77.74; H, 7.65.

(2) 1,1,3,4-Tetramethyl-2(1H)—naphthalenone. This

had a Rt of 23.1 min and showed xiifEtogos mu (log 5 3.91),

239 mu (log 8 3.95) and 234 mu (log a 3.97). Its ir

 

spectrum (liquid film) had principal bands at 1652, 1621

(v and v conjugated) and 1600 cm_1 (shoulder,

C=C C=C’
VC=C, aromatic). The mass spectrum indicated a parent
peak at m/e 200. The nmr spectrum (CC14 soln) showed a
singlet at T 8.60 (6H; ggmfdimethyl), two singlets at T
8.0 and 7.68 (each 3H; allylic methyls) and a complex'
multiplet centered at T 2.76 (4H; aromatic protons). The

nmr Spectrum, when examined at a sweep width of 100 cycles,

33
showed the peaks due to the allylic methyls to be poorly
resolved quartets, J = 0.9 cps.
522$: Calcd for C14H160: C, 83.95; H, 8.05.

Found: C, 83.81; H, 8.01.

(3). 2,2,3,4-Tetramethyl-142H)rnaphthalenone. This

colorless oil had a R of 24.5 min and had the following

t
uv characteristics: A95%EtOH
max

(shoulder, log 8 3.33), 276 mu (log a 3.49), 268 mu (log a

340 mu (log 8 3.14), 286 mu

3.49) and 239 mu (log a 5.05). The principal ir bands

(liquid film) occurred at 1674, 1633 (VC=O and VC=C’

aromatic). The mass spectrum

COD-

1

jugated) and 1600 cm- (v

C=C.
indicated a parent peak at m/e 200. The nmr spectrum

(CC14 soln) contained singlets at T 8.75 (6H; gamfdimethyl),
T 8.05 and 7.90 (éaCh 3H; allylic methyls) and a complex
multiplet centered at T 2.63 (4H; aromatic protons).

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

Found: C, 83.88; H, 8.01.
2. The Reaction with a Large Excess of Oxidant

Three grams (0.016 mole) of 1,2,3,4-tetramethylnaph—
thalene was dissolved in 50 ml of methylene chloride and
oxidized in the presence of 54 ml of 47% borontxifluoride
etherate (0.18 mole) with a solution of peroxytrifluoro-
acetic acid prepared from 41.3 g (0.20 mole) of trifluoro-
acetic anhydride and 4.8 ml of 90% hydrogen peroxide (0.18

mole). The peroxytrifluoroacetic acid solution and boron

34
trifluoride etherate were added concurrently over 80 min,
the reaction mixture being kept below -10°. After further
stirring for 1 hr at -16°, the miXture was washed with
water (3 x 200 ml), saturated sodium bicarbonate (3 x
300 ml) and again with water (3 x 100 ml). The sodium
bicarbonate extract was acidified and extracted with
methylene chloride, which provided on evaporation 0.14 g
of a dark viscous oil. This material was not further
investigated.

The methylene chloride fraction was evaporated and
gave 2.6 g of a deep red viscous oil. Vacuum distillation
(125°, 0.45 mm) of this oil afforded 0.74 g of an orange
liquid. Vapor phase chromatography (20' x 1/4" SE-30
column, 220°, 90 ml/min of helium) showed that the distil-
late had components with retention times of 4.3 min
(5.4%), 12.4 min (40.4%) and 17.8 min (54.3%). The Com—
pounds with the longest retention times were shown by their
ir spectra to be 2,2,4,4-tetramethyl-1,3-dioxotetralin and
1,1,3,4—tetramethyl-2(1H)-naphthalenone reSpectively. The
compound with Rt 4.3 min was not identified, but was found
to be an oil with A95%EtOH

max
and 212 mu, and principal ir bands (CC14 soln) at 1800 (vs),

315, 276 (sharp), 241 (shoulder)

1110, and 1045 (s) cm-l.

D. The Oxidation of 2,2,3,4-Tetramethylel(2H)rnaphthalenone

 

A solution of 56 mg (2.8 x 10-4 mole) of 2,2,3,4-tetra—

methyl-1(2H)—naphthalenone in 4 ml of methylene chloride

35
was oxidized in the presence of 0.1 ml of 47% borQa tﬁfluor-
ide etherate (3.5 x 10-4 mole) with the usual oxidant pre-
pared from 84 mg (4.0 x 10-4 mole) of trifluoroacetic
anhydride and 10 ul (3.5 x 10-4 mole) of 90% hydrogen per-
oxide in 1.5 ml of methylene chloride. The addition took
place over 10 min and the mixture was allowed to stir at
-16° for 30 min. Work-up resulted in the isolation of
51 mg of material. Vpc analysis (10' x 1/4" FFAP column,
235°, 45 ml/min of helium) of the volatile portion indicated
only a trace amount of starting material (Rt 16.0 min) and

almost complete conversion to 2,2,4,4-tetramethyl-1,3-di-

oxotetralin (R 11.2 min), the latter being identified by

t

its ir spectrum.

B. General Photolysis Procedure

 

Unless stated to the contrary, all photolyses were
conducted with a 450-watt Hanovia Type L mercury lamp and
the light was filtered through a Pyrex glass sleeve. The
solution to be irradiated was placed in a Pyrex test tube,
sealed with a serum cap and attached to the outside of a
Hanovia Pyrex immersion well, 2-3 cm from the center of
the mercury arc. This apparatus was then placed in an ice
bath, which maintained the temperature of the solution dur-

ing irradiation between 2 and 6°.

36

F. Irradiation of 242,3,4-Tetramethyl-1(2H)rnaphthalenone

in Ether.

A solution of 115 mg of 2,2,3,4-tetramethyl—1(2H)-naph-
thalenone in 7 ml of ether was irradiated through Pyrex
using a 450—watt Hanovia Type L mercury lamp. The photolysis
was monitored by vpc, aliquots being removed at intervals
of 20-30 min during a total irradiation time of 150 min.
Examination of the samples on a 10' x 1/4" carbowax column
at 225° with a gas flow of 50 ml/min of helium showed a
progressive decrease in the concentration of the naphthalen—

one (Rt 16.6 min) and an increase in the concentration of

a photoproduct with Rt 9.5 min. The concentrations of the

starting naphthalenone and photoproduct were equal after
88 i 2_min. The concentration of the photOproduct reached
a maximum after 120 i 5 min and further irradiation led to
a significant increase in the concentration of another

compound with R 23.6 min at the expense of the initial

t
photoproduct (see Section H). The initial photOproduct

was purified by vpc (above conditions) and shown to be
3,4-benzo-1,5,6,6-tetramethylbicyclo[3.1.01hexan-2—one.

The colorless oil had major bands in its ir spectrum

1 (v aromatic).

(CCl4 soln) at 1699 (vs, VC=O) and 1606 cm C=C'

It is noteworthy that no band appeared for v nonaromatic.

95%EtOH
max

C=C’
The uv spectrum consisted of A 335 mu (log a 2.69),
301 mu (log 8 3.29), 247 mu (shoulder, log 8 4.05) and

225 mu (log a 4.42). The mass spectrum indicated a parent

peak at m/e 200. The nmr Spectrum (CCl4 soln) showed

37

singlets at T 9.28, 8.84, 8.73, 8.49 (each 3H; aliphatic
methyls) and a complex multiplet centered at T 2.6 (4H;
aromatic protons). The two aliphatic methyls at highest
field are tentatively assigned as the gamfdimethyl group
while the.methyls at T 8.73 and T 8.49 are assigned as
the bridgehead methyls at C-1 and C-5 respectively.

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

Found: C, 83.74; H, 8.04.

G. The Dark Reaction of 2,2,3,4-Tetramethyl-1(2H):

naphthalenone in Ether

 

A solution of 9 mg of 2,2,3,4-tetramethyl-1(2H)-
naphthalenone in 0.9 ml of ether was placed in a pyrex
test tube, sealed with a serum cap, and stored in the
dark. The reaction was monitored by Vpc (10' x 1/4"
Carbowax column, 208°, 60 ml/min of helium). Aliquots
were removed after 2 hrs and 168 hrs. No reaction could
be detected after this time and only starting material

was recovered.

H. Further Irradiation of 2L2,3y4-Tetramethyl-1(2H)-

naphthalenone in Ether

A 1.5% solution of 2,2,3,4-tetramethyl-1(2H)-naph-
thalenone in ether was irradiated through Pyrex with a
450-wattHanovia Type L mercury lamp. The photolysis was
monitored by Vpc (10' x 1/4" Carbowax column, 225°, 50

ml/min of helium). Aliquots examined during the first

38
120 min of photolysis indicated a progressive decrease in
the concentration of the naphthalenone (Rt 16.6 min) and
an increase in the concentration of the photoproduct,
3,4—benzo-1,5,6,6-tetramethylbicyclo[3.1.0]hexan-2-one
with Rt 9.5 min (see Section F). However, after 40 min

of irradiation the appearance of another compound (Rt
23.6 min) had been observed. After 120 min of irradiation
the concentration of benzobicyclicketone decreased and
the concentration of the overphotoproduct sharply increased.
The concentrations of the benzobicyclicketone and the over-
photOproduct were equal after 140:4 min and after 200 min
the concentration of benzobicyclicketone was negligible.

The overphotoproduct was purified by Vpc (above con—

ditions) and shown to be 2L3L4y4-tetramethyl-1(4H)-naph-

thalenone. This compound was a white solid, mp 76-78°,

and had A95%EtOH
max

4.06). The ir spectrum (CCl4 soln) had principal bands

 

272 mu (log 8 4.03) and 256 mu (log 8

C011—

at 1648 (v conjugated), 1626 (shoulder,

vc:c’

aromatic). The nmr Spectrum

C=O’

jugated) and 1605 cm-1

(chc'
(CCl4 soln) showed singlets at T 8.52 (6H; gamfdimethyl),
T 8.02 and 7.93 (each 3H; allylic methyls) and a complex
multiplet centered at T 2.57 (4H; aromatic protons). The
allylic methyls at T 8.02 and T 7.93 are tentatively assigned
to the methyls at C—2 and C-3 respectively.

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

Found: C, 84.04; H, 8.18.

39

I. A Comparison of the Rate of Photolysis of 2,3,4y5,6,6-
Hexamethylcyclohexa-Z,4-dienone in Ether and 2,2,3,4-
Tetramethyl-l(2H)—naphthalenone in Ether and Methanol

 

Eleven milligrams of 2,3,4,5,6,6—hexamethylcyclohexa-
2,4—dienone in 1.1 ml of ether, 11 mg of 2,2,3,4-tetramethyl-
1(2H)-naphthalenone in 1.1 ml of ether, and 11 mg of the
tetramethylnaphthalenone in 1.1 ml of methanol were irradi-
ated at the same time through Pyrex using a 450-watt
Hanovia Type L mercury lamp. Each reaction was monitored
by vpc (10' x 1/4" FFAP column, 233°, 45 ml/min of helium).
Analysis of the data indicated that 50% of the hexamethyl-
cyclohexadienone in ether had disappeared after 28:3 min.
It required 55:4 min for 50% of the tetramethylnaphthalen-
one in ether to disappear, and 50% of the tetramethyl—

naphthalenone in methanol was photolysed in 23:2 min.

J. Irradiation of 3.4-Benzo-1,5,6,6-tetramethylbicyclo-
i3.1.0lhexan-2-one in Ether

A solution of 5 mg of 3,4-benzo-1,5,6,6-tetramethyl—
bicyclo[3.1.0]hexan-2—one in 1.0 ml of ether was irradiated
in a Pyrex test tube using a 450-watt Hanovia Type L
mercury lamp. Aliquots were removed after 30 min and 60
min and examined on a 10' x 1/4" FFAP column at 235°
with a gas flow of 45 ml/min. The benzobicyclicketone

(R 9 min) was converted smoothly and efficiently to 2,3,4,4-

t

tetramethyl-l(4H)-naphthalenone (Rt 20.8 min). After 30 min

irradiation 30% of the benzobicyclicketone remained,

40
accompanied by 70% of the cross-conjugated naphthalenone
and after 60 min, 97% of the latter product was present.
The cross-conjugated naphthalenone was identified by its

retention time and characteristic uv Spectrum.

K. The Dark Reaction of 3,4-Benzo-1,5,616—tetramethyl-
bigyclo[3.1.0]hexan—2-one in Ether

A solution of 2 mg of 3,4—benzo-1,5,6,6-tetramethyl—
bicyclo[3.1.0]hexan-2—one in 0.6 ml of ether was placed in
a pyrex test tube, sealed with a serum cap, and stored in
the dark. The reaction was monitored by Vpc (10' x 1/4"
FFAP column, 235°, 45 ml/min of helium). No reaction

could be detected after 234 hours.

L. Irradiation of 3,4-Benzo-1,5,6,6-tetramethylbicyclo-
i3,1.0]hexan-2-one in Methanol

A solution of 4 mg of 3,4—benzo—1,5,6,6-tetramethyl-
bicyclo[3.1.0]hexan-2—one in 0.8 ml of methanol (distilled
from sodium methoxide) was irradiated through Pyrex with
a 450-watt Hanovia Type L mercury lamp. All glassware to
come in contact with the benzobicyclicketone was washed
with ammonium hydroxide, distilled water, and methanol dis-
tilled from sodium methoxide. The photolysis was monitored
by uv and Vpc (10' x 1/4" FFAP column, 235°, 45 ml/min of
helium).

Following the photolysis by uv led to an immediate

decrease of the uv band at 301 mu. The photoproduct had a

41
much greater extinction coefficient and exhibited bands at
254 and 276 mu in methanol. Aliquots examined by vpc in-
dicated a progressive decrease in the concentration of

starting material (Rt 8.4 min) and an increase in the con-

centration of two new compounds with Rt's of 16.6 and 20.8

min.
After 6 min irradiation 70% of the benzobicyclicketone

remained, accompanied by 7% of the material with Rt 16.6

min and 23% of the material with Rt 20.8 min. After 13 min

irradiation 23% of the benzobicyclicketone was present,

19% of the compound with R 16.6 min and 58% of the com-

t
pound with Rt 20.8 min. By its uv and ir Spectra the
compound with longest Rt was shown to be 2,3,4,4-tetra-
methyl-1(4H)-naphthalenone. The compound with Rt 16.6

min was not identified. However, enough of a sample of
this compound was obtained to show that with repeated pas—
sage through the Vpc (above conditions) no thermalrearrange-

ment of the compound occurs on the vpc column.

M. Irradiation of 2,3,444-Tetramethyl-lj4H)—naphtha1enone
in Ether '

 

A solution of 5 mg of 2,3,4,4-tetramethyl-1(4H)—naph-
thalenone in 1.0 ml of ether in a quartz test tube was
irradiated through a Vycor filter with a ZOO-watt Hanovia
Type S mercuty lamp. Aliquots removed after 30 min, 90 min,
and 270 min and examined by Vpc (10' x 1/4" FFAP column,

235°, 40 ml/min of helium) indicated there was no decrease

42
in the concentration of the original naphthalenone (Rt 21.8
min). Only starting material was recovered, as shown by

the ir spectrum.

 

N. Irradiation of 2,3,4,4-Tetramethy1-1(4H)-naphthalenone

in Methanol

A solution of 5 mg of 2,3,4,4—tetramethyl-1(4H)-naph—
thalenone in 1.0 ml of methanol in a quartz test tube was
irradiated through a Vycor filter with a 200-watt Hanovia
Type S mercury lamp. The reaction was monitored by Vpc
(above conditions). A steady decrease in the concentra-
tion of the starting material (Rt 21.8 min) was observed.
Thus 30% of the naphthalenone was photolyzed after 30 min,
60% after 2 hr, and after 14 hrs no trace of starting

material could be detected. However, no volatile material

with Rt < 33.6 min was present.

0. Irradiation of 1,1,3,4-Tetramethyl-2(1H)rnaphtha1enone
in Ether Through Pyrex ’

A solution of 7 mg of 1,1,3,4-tetramethyl-2(1H)-naph—
thalenone in 0.7 ml of ether was irradiated through Pyrex
using a 450-watt Hanovia Type L mercury lamp. The photolysis
was monitored by vpc. .After irradiation for 220 min a
Slight decrease in the concentration of starting naphthalen-
one (R 11.1 min) was observed, but no compound with R <

t t
32.5 min could be detected.

43

P. Irradiation of 1,1,3,4-Tetramethyl—2(1H)-naphthalenone
in Methanol Through Quartz ’

 

A solution of 6 mg of 1,1,3,4-tetramethyl—2(1H)-naph-
thalenone in 1.8 ml of methanol was placed in a quartz test
tube, sealed with a serum cap, attached to the outside of
the Hanovia quartz immersion well, and irradiated with a
450-watt Hanovia Type L mercury lamp. The photolysis was
monitored by Vpc. After irradiation for 130 min a sub-
stantial decrease in the concentration of starting naph-
thalenone was observed, but no compound with Rt < 36.8 min
could be detected.

Q. Reaction of 1,1,3,4-Tetramethyl-2(1H)-naphthalenone
with Methylmagnesium Iodide_

 

1,1,3,4-Tetramethyl-2(1H)-naphthalenone (65 mg, 3.3
x 10'.4 mole) in 1.5 ml ether was added drOpwiSe to a stir-
red methyl Grignard solution at 25°. This Grignard solu-
tion was prepared from 60 mg (4.2 x 10_4 mole) of methyl
iodide and 11 mg (4.5 x 10_4 mole) of magnesium in 2 ml of
dry ether. The solution was then heated under reflux for
30 min. The mixture was hydrolyzed with saturated ammonium
chloride. The organic layer was separated and combined with
the ether extract (2 x 5 ml) of the aqueous layer and dried
over anhydrous magnesium sulfate. Removal of the solvent
left an oil. Vpc analysis (10' x 1/4" Carbowax column, 220°,

40 ml/min of helium) indicated a single product with Rt 9.9

95%EtOH 295 233
max ’ '

min. The colorless oil isolated had A and

44
220 mu. The nmr spectrum (CC14 soln) consisted of a
singlet at T 8.62 (6H; gaafdimethyl), a broad singlet
(hw = 8 cps) at T 7.95 (6H; allylic methyls), two singlets
at T 5.00 and 4.88 (each 1H; terminal methylenes) and a
complex multiplet centered at T 2.97 (4H; aromatic protons).
On the basis of the uv Spectrum (39) and the expected re-
action paths, the product is tentatively assigned the

structure of 1,1,3,4-tetramethyl-2-methylene-1,2-dihydro—

naphthalene.

S UMMARY

1. The oxidation products of 1,2,3,4-tetramethyl-
naphthalene with peroxytrifluoroacetic acid-boron fluoride
etherate in methylene chloride at -12° were: 2,2,3,4-
tetramethyl-l(2H)-naphthalenone (61%), 1,1,3,4-tetramethyl-
2(1H)-naphthalenone (21%), and 2,2,4,4-tetramethyl-1,3-
dioxotetralin (18%). The overall yield was 50%, based on
83% conversion of 1,2,3,4-tetramethylnaphthalene.

2. When 1,2,3,4-tetramethylnaphthalene was oxidized
with a large excess of peroxytrifluoroacetic acid-boron
fluoride etherate in methylene chloride at -10°, no 2,2,3,4-
tetramethyl-l(2H)-naphthalenone was detected. The iso-
lated products were: 1,1,3,4—tetramethyl-2(1H)-naphthalenone
(54%),2,24,4—tetramethyl-1,3-dioxotetralin (40%), and an
unidentified compound (6%).

3. 2,2,3,4-Tetramethyl-1(2H)-naphthalenone was oxidized
with peroxytrifluoroacetic acid-boron fluoride etherate in
methylene chloride to 2,2,4,4—tetramethyl-1,3-dioxotetralin.

4. Irradiation of 2,2,3,4-tetramethyl-1(2H)—naph—
thalenone in ether through Pyrex gave 3,4-benzo-1,5,6,6-tetra-
methylbicyclo[3.1.0]hexan-2-one as the primary photoproduct.
The naphthalenone was found to photolyze one-half as fast
as hexamethyl-2,4-cyclohexadienone.

5. Further irradiation of 2,2,3,4-tetramethyl-1(2H)—
naphthalenone in ether through Pyrex provided 2,3,4,4etetra-
methyl-1(4H)-naphthalenone.

45

46
6. Irradiation of 3,4-benzo—1,5,6,6-tetramethylbicyclo—
[3.1.0]hexan-2-one in ether through Pyrex proceeded SmOOthly
to give 2,3,4,4-tetramethyl-1(4H)-naphthalenone. When the
photolysis was carried out in acid-free methanol, 2,3,4,4-
tetramethyl-l(4H)-naphthalenone was again the major photo-
product (75%), but an unidentified product (25%) was also
detected. The photochemical relationship of the unidenti—
fied product to 2,3,4,4-tetramethyl-1(4H)-naphthalenone was
not established. '

7. 2,3,4,4-Tetramethyl-1(4H)-naphthalenone was re-
covered unchanged from irradiation in ether through a Vycor
filter. Irradiation of the naphthalenone in methanol led
to a steady decrease in its concentration, but no volatile
products could be detected by Vpc.

8. Irradiation of 1,1,3,4-tetramethyl-2(1H)-naphthalen-
one in ether through Pyrex or in methanol thrOugh quartz
resulted in a decrease in the concentration of starting
material, but no volatile products were detected by vpc.

9. Control experiments demonstrated that none of the
photochemically interesting compounds studied were reactive

in the dark with the solvents used in the irradiation studies.

10.

11.

12.

13.

14.

15.

16.

17.

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47

18.

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48

Bellamy, L. J., "The Infrared Spectra of Complex
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).
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49

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47 (1961).

APPENDIX

50

51

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