The catalytic action of metal salts on the borohydride reduction of α-bromoketone

Tetrahedron Letters in Great Britain.

No. 15, pp. 513-515,

1961.

Pergamon Press

Ltd.

Printed

THE CATALYTIC ACTION OF METALSALTS ON THE BOROHYiXiIDEREDUCTION OF a-BROMOKETONE Toshio Department

Goto and Yoshito

of Chemistry, Chikusa,

ALTROUGHsodium borohydride bromohydrins, Henbest

et al.2

borohydride they

treated

completely

debrominated

a debrominated

of

with

of

of

the bulky

acetate 1 2 3

in the reaction

(I)

mixture,

attack of

lead

an a-bromoketone

3

E.R.H.

Jones,

A.A.

alters and gives

methanol-dioxane,

(I)

gave exclusively

(II).

The front-side

obtained

Wagland,

steric

When added a trace

7aattack

hindrance of

lead

and T.I.

acetates,

Wrigley,

J.Chem.Soc.

“Chemically pure” methanol sometimes contains enough heavy metals Distillation of the solvents or addition catalyze debromination. EDTA to the solution is effective to avoid debromination. 513

of

was cholestane-3p,5a-

For reduction of 5a- and 7a-bromocholestane-3p-ol-6-one D.J. James and C.W. Shoppee, J.Chem.Soc. .$22l+ (1954). H.B. Henbest, 2477 ( 1955).

ion

atom.

a-bromohydrin.

groups.

the product

sodium

on bromine

would be due to a large

and Sa-acetoxyl

For example,

3$-acetoxyergostane-11-one;

in purified

3,5-diacetate

affords

with

a trace of

diacetate

on the bromoketone 7a-bromine

only

the expected

sodium borohydride

bromocholestane-3B,5a,6a-triol ion

usually

are obtained.

hydride

reduction

7a-bromocholestane-3b,Sa-diold-one

a hydride

compound,

that

borohydride

compound instead

When treated

products

initial

a new finding

the course

a debrominated

of a-bromoketones

a mechanism involving

We wish to report

1961)

3P-acetoxy+-bromoergostane-ll-one

and obtained

suggested

Japan

17 July

reduction

’ in some cases

Nagoya University

Nagoya,

(Received

Kishi

to of

Catalytic action of metal salts

514

No.15

4?*-.

AcO'

Br

AoO 0 I

diol-6-onediacetate (III),which is not further reduced in the condition employed. The effects of lead and some other substancesare summerizedin Table 1. Table 1 Substance added

Bromohydrin (II) (%)

Ketone (III) (%)

0.25mg Pb as Pb(OAc)2

0

100

0.25 mg Pb as Pb(N03)2

0

100

0.04 mg Pb as Pb(OAc)2

25

75

0.02 mg Pb as Pb(OAcj2

60

40

0.01 mg Pb as Pb(OAc)2

70

30

2.9

70

30

0.25 mg Ba as BalJ12

45

55

0.24 mg Ag as AgN03

55

0.26 mg Hg as H~(OAC)~

45 0

100

0.22 mg Ni as NI(OAC)~

0

100

mg Sn as SnC12

0.20 mg Bi as Bi03Na

70

30

0.20 mg Cu as CuSO4

35

65

2.5 ml H20

100

0

2.0 rng(C6H5C00)2

100

0

5.0 mg HCHO

100

0

5.0 mg (CH3)2C0

100

0

0 100 5.0 mg,HCOOH Condition -.Sodium borohydride(0.20 g) is added to a solution of the bromoketone(0.20 g) and a giGen weight of-metal salt (or other substance) in a mixture of methanol (20 ml) and dioxane (30 ml). After allowing to stand for 45 mir.at room temperature,the reactionmixture is acidifiedwith contd.

Catalytic

No.15

action

of metal

salts

515

acetic acid and diluted with water (50 ml) to give precipitates that collected and dried. The composition of the mixture is calculated from special bands of its 12. spectrum. Accuracy is about? 3%.

The possibility excluded

by the

the ketone

(III)

bromoketone

(I)

acetate

and is

fact

involving

that

with first

of

for

reactions

borohydride order

an excess is

an intermediate

the bromohydrin

in the reaction

presence both

of

with

borohydride. therefore

(II)

condition. is J& respect

(II)

is

is not dehydrobrominated The reaction

affected

rate

by the addition

to the bromoketone

An existence suggested.

bromohydrin

of

(I)

of the of

lead

in the

a common intermediate

to