Stereochemistry in the palladium-catalyzed rearrangement of some cyclohex-2-enyl acetoacetates

Tetrahedron Letters,Vo1.23,No.50,pp Printed in Great Britain

STEREOCHEMISTRY

5279-5282,1982

IN THE PALLADIUM-CATALYZED CYCLOHEX-Z-ENYL

J.C.Fiaud

0040-4039/82/505279-04$03.00/o 01982 Pergamon Press Ltd.

REARRANGEMENT

OF SOME

ACETOACETATES

and L.Aribi-Zouioueche

Laboratoire Universite

de Synthese Paris-Sud,

Asymetrique,

91405-Orsay,

associe

au CNRS LA 255

France.

Summary The palladium-catalyzed acetoacetates ration,

decarboxylation

and rearrangement

to give the corresponding

indicative

The reaction

of an enolate

addition

from the trans-isomer

We have recently

reported

tes by the pre-formed

methyl

of -cis-5-substituted-cyclohex-Z-enyl

ketone proceed mostly with retention

to the s-allylic

ligand

of configu-

trans to the palladium.

is not stereoselective.

that the palladium-catalyzed

lithium enolate

substitution

of acetone

occurred

of allylic

5-ketocarboxylates

of cyclohex-2-enyl

with overall

retention

aceta-

of configura-

tionl. The palladium-catalyzed

rearrangement

ceed under mild conditions, $&

from decarboxylation

tone (3

in moderate

To compare

palladium

(II) enolate intermediate

of the T-ally1

palladium

(II) B-ketocarboxylate (ZJ, to give the ke-

to good yields

the stereoselectivity

with -cis-5-phenylcyclohex-2-enol

of attack of the -~ in situ produced

were collected

by Kugelrhor

ti

enolate with the external-

out come of the palladium-catalyzed

acetoacetates

(3

prepared

by reaction

(5a)5 and c&-5-isopropylcyclohex-2-enol

in THF (20 ml) in the presence

for 12 h at 55OC. After aqueous

(A), produced

233.

ment of the 5-substituted-cyclohex-2-enyl

(4 mol)

has been shown to pro-

via a r-ally1

ly added one, we looked at the stereochemical

(2

(2

of 0.2 mm01 Pd(OAc)2

work up, the elimination

distillation

The results

5279

product

(5$6

rearrangeof diketene4 (Scheme 1).

and 0.8 mm01 PPh3 were heated (1,3-diene)

are shown in Table

1.

and ketone

(2

Pd(OAc),, f’phz

a:R=Ph b: R = iPr Scheme

Table

1

1

(Only one enantiomer

: Stereochemical acetoacetates

results

is shown)

in the palladium-catalyzed

made up from allylic

alcohols

rearrangement

0.

Ketone

cis/trans --

purity a

(cis/trans

(yl)

ratio) a

Yields

c&-(5.$)

95:5

($1

80:20

53

c&-(5b)

91:9

(2)

86:14

45

cis(-)-carve01

91:9

carveylacetoneC

a5:15

42

trans-(5a) -JvL

24:76

(3)

66:34

45

a) Determined

by g.1.c.

b) Isolated material

(capillary

column,

with satisfactory

of

(%) b

OVl, 15 m).

elemental

analysis.

c) Racemic.

-Cis and trans

(2)

were prepared

dium salt of t-butyl Scheme

acetoacetate

for comparison

by the palladium-catalyzed

with the corresponding

acetate

reaction

(8J7, according

of the so-

to the

: OAC

/

@~~02t-=u ‘COCH 3

toluene,

Pd(dba)2~dPPe,

g

At *v

THF R

CH.$OCH,

/

P-TsOH

R

R

5281

The reaction

was assumed

to proceed with overall

shown for the palladium-catalyzed The Table

indicates

retention

of configuration.

logy to the acetate that the enolate

reaction

Provided

group)

ion rather the n-allylic

previously

stereochemistry

described

xesll and to allylic

acetates

both -cis- and e-(z) loss of selectivity

allylic

acetates

12

of the acetoacetate

occurs with inversion

acetates'.

proceeds with major

10

group

rearrangement

attacks

of e-(7a)

than under-

stable

palladium

of (-)cis-carve01 -

of a a-ally1

palladium

comple-

led to

(II) complex.

As it was checked

in the conditions process,

acetoacetate,

with the

reaction'.

was not stereoselective.

to a competing

of the starting

to r-ally1

of the acetoacetate

the intermediacy

(in ana-

, these results suggest

ligand trans to the palladium

were stereochemically

epimerization

on cyclohexenyl

of %-(a

of attack of ketone enolates

can be attributed

as it has been

from the metal center. This is the agreement

confirming

the rearrangement

rearrangement

in the palladium-catalyzed

the palladium-catalyzed

racemic -cis-carveylacetone,

assisted

delivery

of configuration

enolates

that the displacement

by the Pd(0) complex

transfer

Nevertheless,

of stabilized

that the palladium-catalyzed

going intramolecular

Moreover,

retention

of the reaction,

that the

that could likely be a palladium-

in analogy

to the process described

with

.

ACKNOWLEDGEMENTS The authors Precieux"

thank Professor

H.B.Kagan

for a loan of palladium

On of us (L.A.Z.)

is indebted

for fruitful

chloride.

discussions

Financial

to the Ministere

support

Algerien

and "La Compagnie by the C.N.R.S.

de 1'Enseignement

des Metaux

is acknowledged

et de la Recherche

for a fellowship.

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5282

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showed different

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(7 upon refluxing .I$

chromatographic

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: 13C n.m.r.

led to the alkylation

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(3

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W-(7&) 127.16

saponification

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according

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(3

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