Enolstannanes as electrofugal groups in allylic alkylation

Tetrahedron Letters Vol. 21, PP 2591 - 2594 @Pergamon Press Ltd. 1980. Printed in Great Britain

ENOLSTANNANES

AS ELECTROFUGAL

Barry M. Trost" McElvain Laboratories of Organic Department of Chemistry University of Wisconsin Madison, Wisconsin 53706

0040-4Oj9/80/0701-259ljbO2.00/0

GROUPS

Chemistry

IN ALLYLIC

Ehud Keinan Weizmann Institute of Science Department of Organic Chemistry Rehovot, Israel

12

ABSTRACT: Enolstannanes serve as nucleophiles the influence of palladium(O) catalyst. Nucleophilic generally

substitution

requires 1

ketosulfides,

etc.

ally1

in the presence

acetate

but gave

Simple

the dialkylated

in 34% yield. variation

silyl

ally1

acetate

ally1

acetates. Switching

ether

carbanions enolates

such

the

to enol

as that

the reaction

stannanes

from

alkylate (1) product

for monoalkylation

by

failed.

the monoalkylated

not be extended

Use of

product

with

to substituted

as 2 2,3 led to a remarkably

OAc

& /

rapid

and

Cph3p14pd \

6mozoalkylation

Several

aspects

for alkylation

are quite

(4, 6 6.14 5.44,

The

temperature

noteworthy.

differs

and

6.40,

J = 14.8

based

upon

J = 16 Hz;

Hz).

The

as summarized

a high

from

olefins

the reactions

such

the coupling 6, 6 5.27

and

stereochemistry

2591

in the Table.

regioselectivity

end of the ally1

of the trisubstituted

of the disubstituted

is assigned

in THF First,

substituted

latter

stereochemistry

In the case chemistry

at room

at the less

of the E isomer. the

)W

&

2

and

B-

0 \

where

of

acetophenone

conditions

(C$-&SnU

clean

under

by palladium anions

and the monoalkylated

only

could

such

catalyzed

acetates

(triphenylphosphine)palladium

reaction

gave

allylic

as malonates,

selectivity

or other

of acetophenone

(59%), but

acetates

in 65% yield

to improve solvent,

towards

such

of tetrakis

product

Attempts

of catalyst,

the enol

of allylic

stabilized

ALKYLATION

double

is seen

moiety4

with

with

anions retained. 4,5

bond

formation

stabilized was

as 4, -- 6, and 8, the stereoconstants of the vinyl protons 5.43,

3 = 15.3

HZ;

of the trisubstituted

f, 6 5.32 olefins

is

2592

Alkylation of Enol Stannane 2

Table. Entry

Ally1 Acetatea

1

_OAc

2

Ph.+_OAc

b (hr)

Time

uOAc=

4

LOAc

% Yieldd

1.1;1

90-95

24

1.2:l

82

2.3:1

89

1.8:1

78

1.4:1

96

0.5 OAc 19

5 Br*

ProductC

1

42

3

Ratio 2:Acetate

1.5:1

&

Br 89 I

6

;“;Lv,

3

2.2:1

91 W

OAc 7

8

10

OCZHS 4f OAc

8 OCzHs f

41

1.3:1

42

l.l:l

22

3.8:1

24

2.2:1

+

72

24

85

a) All reactions were carried out at room temperature in dry THF using approximately 5 mol 8 of catalyst 2. For example, 287 gm (1.46 mmol) of a mixture of geranyl and neryl acetate and 1.08 g (2.69 mmol) of 2 in 6 mL of dry THF were stirred for 42 hr at room temperature in the presence of 73 mg (4.3 mol %) of 1 After preparative tic (1:9 ether:hexane), the colorless oil was distilled & a Kugelrohr apparatus at 110-130' (pot temperature) @0.2 mm to give 238 mg (78%) of 5. b) In most cases, monitoring the reaction by tic showed disappearance ally1 acetate in less time than the time allotted.

of the

c) All new products have been fully characterized by spectral means and for elemental composition.

d) Yield

after

e) Nixture

distillation

of neryl

f) Prepared

unless

and geranyl

by Dr. Dennis

otherwise

noted.

acetate.

Curran

and will

be reported

g) Prepared by Dr. Michael Miller from the aldehyde Michael Rosenberger of the Hoffman-LaRoche Co. h) In this

assigned from

case,

mainly

the product

mixtures

thermodynamic

methyl

groups

The ester

(6 1.59,

ether

9 and (entry

cyclopentanone

a

that

For

6H and

3H) supported

101,

a ketone

7).

The utility

(entry

sequenceas

tic.

isomer

which

by Dr.

is produced

should

re-

shifts

of the vinylic 6 assignment.

this

6), an alkyl

of the sequence shownbythe

(even

therefore

by the compatibility bromide

of an

(entry

is illustrated

51, and by the

7 of 9 to 13 *"+

facile conversion

1)5%

HCl/H,O &

OCzHs OSnIC4Hg)3

2

HOC4Hgq

2

can be obtained

isolating

any

lx?

in 84% overall

yield

from

the enol

stannane

without

intermediates.

The regioselectivity generation with

a single

materials)

as evidenced

I

which

only

provided

by preparative

5, the chemical

1.66,

is high

annulation

only

of starting

stability.

chemoselectivity

(entries

an enol

purified

on the observation

stereoisomeric

flect

was

separately. kindly

of the enol

appears stannane

tri-n-butylstannylchoride3) -

to depend

on the reactants.

For

example,

14 in situ (by treatment of the lithium enolate -_ and cinnamyl acetate led only to the desired

26% overall product 15 E,Z mixture in a 1:1.2 ratio, separable by _-_ as a -On the other (15E, 6 1.04, d, J = 7 Hz, 3H; 152, fi 1.10, d, J = 7 Hz). ___ -_-+ hand, reaction with the much more sluggish' 2-ethoxyallyl acetate led only to 2,6-disubstituted

tic

9, the product acetates

from

the more

equilibration

stable

of the enol

enol

stannane.

stannane

Thus,

appears

with

to occur

sluggish

faster

ally1

than

alkylation. Two mechanisms to transfer complexes

may

the alkyl have

been

be envisioned.

group

formed

The

to palladium from enol

fact

that

organostannanes

appear

very well' and that oxa-n-ally1 10 makes path “a' quite silyl ethers

2594

Pd

c

product

&"

direct attack at C

quite

reasonable.

fined

for other

tion

occurs

stabilized

Path

stabilized tion

net retention anions 4,ll strongly of the

nucleophiles

enolate

for a generous most

We wish

support

generous

of our

supply gift

supports

scope

the

a much

than

to thank

of several

latter

acetates

enol

for

to the

stannanes

less

of this might

reacbe more

them.

Science Drs. and

found

pathway.

applicability

accorded

thank

10) as also

alkylation

that

the National We also

ally1

(entry

broader

suggests

presently

programs,

of methyl

type of reaction that has been de4,ll . The fact that substitu-

of the allylic

and also

equivalents

the

as malonates

of configuration

suggests

synthesis

Acknowledgement. generous

such

with

in organic

useful

"b" represents

nucleophiles

The expansion

product

Foundation

M. Miller

for their

and D, Curran

Dr. M. Rosenberger

for a

8-oxo-3,7-dimethylocta-2,4,6-triene. References

1. 2. 3.

For a review see B. M. Trost, Tetrahedron, 3, 2615 (1977). Y. Odii and M. Pereyre, J. Organomet. Chem., 55, 273 (1973). For alkylations with halides see Ref. 2 and P. A. Tardella, Tetrahedron Lett., 1117 (1969). 4. B. M. Trost and T. R. Verhoeven, J. Org. Chem., 41, 3215 (1976); J. Am. for publication. Chem. Sot., accepted 5. With amines as nucleophiles, high stereoselectivity for the E isomer was also seen. B. M. Trost and E. Keinan, J. Org. Chem., 44, 3451 (1979). 6. J. W. K. Burrell, R. F. Garwood, L. M. Jackman, E. Oskay, and B. C. L. Weedon, J. Chem. Sot., C, 2144 (1966). 7. R. Fraisse-Jullien and C. Frejaville, Bull. Sot. Chim, Fr., 4449 (1968). 8. Cf. B. M. Trost and F. Gowland, J. Org. Chem., 44, 3488 (1979). 9. Chem., 129, C36 (1977): M. Kosugi, Y. Shimizu and T. Migita, J. Organomet. D. Milstein and J. K. Stille, J. Org. Chem., 44, 1613 (1979): R. F. Heck, J. Am. Chem, Sot., 91, 6707 (1969). 10. Y. Ito, H. Aoyami, T. Hirao, A. Mochizuki and T. Saegusa, J. Am. Chem. 494 (1979) and earlier references cited therein. sot., E, 11. B. M. Trost, T. R. Verhoeven, and J. Fortunak, Tetrahedron Lett., 2301 (1979). 12. Work performed in these laboratories. (Received in USA 13 February 1980)