Direct conversion of oxiranes to alkenes by chlorotrimethylsilane and sodium iodide

Tetrahedron Letters, Vo1.22, No.36, pp 3551 - 3552, 1951 Printed in Great Britain

DIRECT BY

Romualdo

CONVERSION

OF

Institute

Lorenzo

of Organic

AND

Mangoni,

TO

ALKENES

SODIUM

Orsola

and Biological

Via Mezzocannone, Abstract:

OXIRANES

CHLOROTRIMETHYLSILANE

Caputo,

0340~4OJ9/81/36j551-02$02.00/O @1981 Pergamon Press Ltd.

IODIDE

Nerl,

Chemistry

Giovanni

Palumbo

of the University

16 - Nap011 80134

(Italy)

Smooth and quantitative conversion of oxiranes to alkenes is achieved by treatment with in situ generated iodotrimethylsilane.

In connection that oxlranes

with other work concerning

can be very fast, smoothly

with chlorotnmethylsilane our experimental

and sodium

conditions,

hydroxylation

of steroidal

and quantitatively

converted

iodide in acetonitrile

2a,3a-epoxy-5a-cholestane

olefins,

to alkenes

we have found by treatment

at room temperature.

was quantitatively

Indeed, under

converted

to 5a-chole

stane in only half an hour. The reaction sly substituted

oxiranes

last two entries the startinq

seems to be quite general are reported.

oxirane

assumed

pathway

to follow

is concerned,

of fact, H.Sakurai,

iodotnmethylsllane

of silylated

iodohydrins.

from the iodohydrin

probably

owing to the better solubility

of

constant

by silylation

of oxiranes

to alkenes may be

.. 1

and A.Hosomi

in benzene

Under our experimental

of sodium

for by further

prepared

solution

that the reac-

leads to quantl-

the subsequent

attack of excess

eli-

iodide ion

as well as to the much

with benzene.

in an independent

known' lodohydrin. ’

3551

reported'

conditions,

iodide in acetonitnle

of the latter in comparison

of the already

have recently

with oxlranes

may be well accounted

In this view, we have therefore 5a-cholestane

to the

having the same conflguratlon

the conversion

LO%Me,

K.Sasakl

mination

higher dielectric

according

the scheme:

1

tion of in situ generated tative formation

is stereoselective

of variou-

is formed.

”

As a matter

gxygen elimination

in the table in both of which only the alkene

As far as the reaction confidently

as shown in the table were a few examples

way 26-iodo-3a-trimethylsilyloxy-

The crude product

(P.M.R. 6 3.81,

3552

Table.

Conversion

of oxiranes

to alkenes

Oxirane

by Me3SiCl

Timea

and sodium iodide.

Yieldb

Alkene

2a,3a-Epoxy-5a-cholestane

30'

96

5a-Cholest-2-ene

4a,5a-Epoxy-cholestane

20'

95

4e,56-Epoxy-cholestane 5a,6a-Epoxy-cholestane

20'

95 97 96 94

Cholest-4-ene Cholest-4-ene

20' 15'

2a,3a-Epoxy-38-methyl-5a-cholestane cis-1,2-Epoxy-4-tBu-cyclohexane

3-Methyl-5a-cholest-2-ene

93

4-tBu-Cyclohexene 4-tBu-Cyclohexene

30'

94

Cyclohexene

92 95

(Z)-2,2'-Dimethyl-3-hexene

20' 20'

trans-1,2-Epoxy-4-tBu-cyclohexane Cyclohexene oxide

Cholest-5-ene

(Z)-2,2'-Dimethyl-3-hexene

oxide

45'

(E)-2,2'-Dimethyl-3-hexene

oxide

45'

(E)-2,2'-Dimethyl-3-hexene

a TLC OP GLC monitored. b Yield of crystallized or distilled product. Purity : &? %. 4.43) was then directly

dissolved

lution at r.t. (see exoerimental consumed

(TLC) and workup

tion: 93% conversion A typical in anhydrous

tes, to the thus obtained mmol)

in anhydrous

red solution

turned

(TLC). Usual workup 20 ml) and washing

pale yellow

chloroform

- addition

iodohydrin),

suspension

to a red-brown

the starting

stirred

a solution

to convert

reliability

of such a procedure

halohydrins

directly

was entirely

(after crystalliza-

of sodium

iodide

(3.9 mmol)

under 112. After few minu-

of 2a,3a-epoxy-5a-cholestane

(1.3

(1 ml) was slowly added. The stir-

colour and after 30' the reaction was complete (20 ml), extraction

with Et20 (3 x

- then led to a crude crystalline

from hexane had m.p. 74-75",

be utilized

solution

when soluble)

layers with water

to note how the above results

material

thus proving our above assumption.

of 5 N aq sodium thiosulphate

of the ethereal

iodide being added to the so-

(1.9 mmol) was added dropwise

(or acetonitrile,

immediately

sodium

gave crude 5a-cholest-2-ene

To a magnetically

(5 ml) Me3SiCl

which after one crystallization It is worth

mixture

to the starting

follows.

acetonitrile

acetonitrile,

below). After few minutes

of the reaction

referred

procedure

in anhydrous

suggest

to alkenes,

IO/D +70" (1.8 mmol; Y. 94%).

that our experimental Work is already

and results will be reported

product

conditions

in progress

in a forthcoming

might

to check the

paper.

REFERENCES 1. H.Sakurai, reaction

of oxiranes

2. R.C.Cookson 3. O.Ceder

(“ecelved

K.Sasaki

and A.Hosomi,

Tetrahedron Letters, 2329 (1380). See also Ref. 3 for the

with chlorotrimethylsilane.

and J.!f.Coxon,

and a.Hansson,

in UK 25 June

J. Chem. Sot., 1466 (1971).

Acta Chem. Stand., B 30, 574 (1376). 1331)