Camphor enol and homoenol acetates

T&r&e&on

Letters N0.37, pp. 3613-3617, 1967.

Pergamon Press

Ltd.

Printed

in Great Britain.

CAMPHOR ENOL AN0 HOMOENOL ACETATES

G. C.

Joshi,”

Department

W.

of

Chambers.**

D.

Chemistry,

and E.

University London,

of

W. Warnhoff

Western

Ontario

Canada

(Receivedin USA 22 May 1967)

Camphor certain

acetate

a-substituted

usual (b)

enol

methods acetic

(II-H

camphor

[(a)

acetic

anhydride

and

anhydride sulfuric

at

138", (d) isopropenyl

chloride

at

5Z”]

acetylation

by the

camphene with

2.90

ponent

*

(

I I I) .

tricyclene

times

Attempts

to

acetate

and

camphor

this

acid

160". (c) acetic

at

for

prepare

and e-toluenesulfonic acid

recovered

intermediate

sulfuric

and no evidence

at

for

g6”,

the

preparation

compound

200°.

and boron and

(e)

formation

of

by the

138" and at

at

anhydride

acid

the

tr i-

acety 1

of

any

of

camphor

product.

Therefore, acetate

a promising

derivatives.

fluoride

gave

seemed

min.

A could

Commonwealth

resort lead

was had

tetraacetate

Repetition gave

a crude

to or

of

this

the

tetrapropionate reaction

from

1

described

preparation

oxidation

of

according

(45% yield)

product

(A,s85%) and 5.40 min. be separated

previously

showing

(&~15%). ' The

in a state

to

of

less

go-95%

the

tricyclene

published

Bursary

GLC peaks

polar,

lower-boiling

purity

by fractional

(1965-66)and Studentship(1966-present).

3613

procedure

two major

Scholar 1964-67.

** Holder of a NRC

(I)

of

en01

and (2) retention com-

distillation,

3614

No.37 b.p.

62-64”

(9.5

mm.)

A pure

sample

of fi

a 2-m.

column

of

potassium

1% butanediol

workers

their

compound.

(Fig.

la).

quaternary

VI-H

but

instead

ication

The

ready

sis

should

on

ts

the

be of

l-2%,

the

mainly

is of

any,

of

Chromosorb

(IV-H),

assignment

the

camphor

camphene

camphor

acetate

until

of later

II

except

from

to

a crude

its

the 1750

OAc)

product

by the VI-H

to

(3

(ester

and

C=O),

that

A is

which (d.

phenomena that

used

NMR spectrum

a convenient

note

Methanolic

NMR spectrum

acetatetll)

(OH for

GLC on

structure

show clearly

homoenolization

I gave

from

360)

150”.

had been

of

2,6-homoenol

homoenol

P at

in

(A-H),

3055

alumina.

by preparative

acetate

evidence

(c::tH

studies

enol

combined

spectrum

the

the

absorption

vcs mai

-via

free

of

on neutral

reaction

hydrogen

2.6-homoenol

reserved

which

spectrum

unrecognized

in current

formation

on siliconized

and

infrared

camphor

interest

if

camphor

by chromatography was obtained

no vinyl

ultraviolet

to

of

oxidation

than

the

hitherto

availability

tetraacetate more

and

reverts

mode of

to

groups),

cm.- 1 (C-O-C),

for

or

analysis

camphor

&exhibits

hydrolysis

1225

basis

(2)

spectral

A into

the

However,

methyl

oni

as

for

succinate

converted (1.2)

The

by Heya

I§ , C12H1802,

hydroxide

Japanese

as described

ref.

in our which

on sap3).’

one-step (3b);

not

synthecomment

hands

contained

lead not

II.

-? .

I

IV In formulas ’

A 2-m.

V IV,

column

V and VI,

of

R=H.

1% butanediol

’ The formal possibility that by the fact that methanolysis which has a proton at C4 that quinone .

Cfi.

or

VI

Br.

suctinate

on Chromosorb

P at

130° was used.

A is the homoenol acetate with a C2-CQ bond instead is excluded with sodium methoxide produces camphor zf A in methanol-O-dl. can-be seen in the NMR spectrum of the derived camphor-

No.37

3615

la

2.01

lb 2.33

Fig.

NMR Spectra

1.

These first

frustrations

thought

undergoes

less

carbonyl

(6),

lithium

there

that

with

relative

rate

of

point

of

exclusion

which

to

generate lithium

Camphor

promising,

is

any

stronger

V-H

original

goal

Although

it

so formed

with

in CDCls

forced has

(4.5).

reagents

carbonyl

In fact, anion

Acetates

been

several

quantitatively. with

acetic

is

of

reported

camphor

of

in

the

best

that

at

(5)

these

IV-H

has

method

reagents.

We

-50”

the

increased we have

acylation gives

other,

and phenyl-

room temperature

Moreover, anhydride

60 MC/S.

consideration

at

addition

this

at

methyllithium

base n-butyllithium to

addition. enolate

and Enol

enolization

abstraction

camphor enolate

Grignard

extensive

somewhat

a-proton

the

approaches. with

also

the

of

Homoenol

in achieving

addition

now find

camphor

of

to found

of only

the

the in

at

3616

No.37

0-acylation

with

product

(cf. -

(Foote

Mineral

no amount

ref. Co.)

tetrahydrofuran acetic

a single

at

peak

one

vinyl

6 2.10

-1200

cm. -l

3-bromocamphor -

ppm.

110’

b.p.

92 -

*

singlets).

removal

in

addition

and

the

of

the

enol

mm.),

[a],

+ 37.6” In

reaction

acetic

(8.5

of

64 rmnoles of

(+)

by addition

8.00

with

7.88

(5,

ppm.

(J = 3.5

200 ml.

of

mmoles)

g.

(81%)

of a

which

gave

(Fig.

lb)

methyl

C=O), 1610 and 1630 215mu

dry

of

in CHCl3)

and an acetate

[Xinf EtoH

crude

‘Ilithium

The NHR spectrum

cps.)

(ester

spectrum

8.16

the

(E 3600)]

singlet

(C=C),

and

establish

its

enol

acetates

The (5,

of

in CHC13),

acetate

&I-Br)”

dCDC1 3 0.77,

and

0.95,

mixture

by distillation

0.93,

1.03,

to

with

116’ ppm.

proton

acetates 40% of

and 2.16

-

and 2.15

enol

give

had b.p.

1.04, 114

competed of

and

bl-Cb””

had b.p.

debromination the

(IV-CL)

6CDC13 0.77.

acetate

3-bromocamphor

was separated

3-chlorocamphor

3-chloro-2-bornenyl

10.40

in CHCls),

of

formed

VI-H

on

and 54%

VI-Et-.

The availability why it

was not

produced

anhydrlde,

sodium

up without

aqueous

of

camphor

by the

acetate contact,

usual

enol

acetate

procedures.

and one equivalent it

was found

to

of have

provided

§§ Satisfactory

analyses

have

been

obtained

for

the

When VI-H acetic been

acid

this

opportunity

was heated at

transformed

A small amount (~5%) of recovered camphor was obtained, of the enolate anion by traces of acid in the anhydride. separated by chromatography on alumina.

tt

(100

on GLC analysis+.

n_-butyllithium,

anhydride

of

+ 16.5”

[a],

CSZ [vmax 1765

liquid

case

in

10 ml.

of

c-buty

dissolved

up and distillation

3-bromo-t-bornenyl

(z,

camphor

NMR spectrum

&l-l$t.

+ 41.6”

the

a solution

mm.),

3 5.54

prepared.

while

the

work

3.40min.

acetate

were

in

of

ultraviolet

the

detectable

followed

spectrum

same manner

[aJD

mmoles)

93”

COCl

infrared

singlets),

m.),

6

of

after

time at

(IV-Br)

(methyl

of

the

(8.8

(methyl

(10.5

yielded

as camphor

the

(50

-50”

hydrogen

(C-O-C)]

In

g.

retention

ppm.,

structure

108

59

of

7.7

addition

room temperature

at

1 iquid,

C-acylatlon

Thus, to

at

anhydride

colorless

with

7)‘.

of

150”

to determine with

for

entirely

acetic

4 hours into

and b.

Led

camphor.

presumably from protonation The en01 acetate was easily

compound.

Camphorend acetate was probably obtained by Malmgren (8) as one of the products from the reaction of bromocamphor (IV-Br) with magnesium followed by acetic anhydride, but the colorless liquid obtained was not characterized by this worker.

No.37

.3617

Likewise,

when VI-H

p-toluenesulfonic Treatment at

of

was heated

VI-H

with

room temperature

acylation stable difference

between

increased

angle

bicyclo[2.2.1] methyl

and

groups

for

camphor

anhydrous

camphor

and

(presumably)

and acetyl

should

even

and other strain

system

(B),

as well

work

was generously

enol

as

acetate

ketones

involved the

in

steric

or

acetone

in carbon in

is

for

presumably

introducing repulsion

the

enol

the

acetate.

reversible less The

acylation. with

bond

acetate

of

tetrachloride

associated

a double of

a trace

thermodynamically

reagent

is

and

isopropenyl

Therefore,

be a powerful

simple

torsional

chloride

chloride.

camphor

and

of

with

in acetyl

earlier,

VI-H

10 hours

into

chloride.

camphor

mentioned

camphor,

120°

was changed

hydrogen

gave

reactions than

it

acid,

at

into

the the

and bridgehead

VI-H. This

Acknowledgment.

supported

by the

National

Research

Council

of

Canada.

REFERENCES 1.

(a) Y. Matsubara, Nippon Kagaku Zasshi. 2, 726 (1957); Chem. Abstr. Nippon Kagaku Zasshi, go. 289 (1959); Chem. Abstr. a: S. Wakabayashi,

2.

Y.

Heya,

Nippon

Kagaku

3. (a) A. Nickon, J. L. (b) J. 3354 (1966). Meeting (ly67), paper

4.

P.

Malkonen,

5. M. L. 6. M.

Ann.

Capmau,

Lipp

7. (a) H. Ritchie

and

D.

Acad.

Bernstein,

Ber.

9. P.

J.

R.

Schleyer,

Scient.

&,

Fennicae, and

P.

Cadiot,

Naturwissenschaften,

V. Kramar, Lyman, J.

8. S. M. Malmgren,

(1959);

Chem.

Abstr.

s:4571c.

Lambert. R. 0. Williams and N. H. Werstiuk. J. Am. Chem. Sot. L. Lambert and A. Nickon, Abstr. of 153rd Amer. Chem. Sot. O-l 1.

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House and and D. J.

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A.

II

Chemica,

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