An unusual regioselective anti-markovnikov hydration of alkenes with zinc borohydride on silica gel support

Tetrahedron Lcmrs, Vol. 34. No. 29. pp. 4659-4662.1993 Priitcd in Great Britain

An Unusual

0040-4039/93 $6.00 + MI Pcrgamon Rcss Lid

RBQiDSElECtiVB Anti-Markovnikov Hydration of Alkenes With Zinc Borohydride on Silica Gel Support

Brindaban

C.

Department Cultivation

Ranu*,

Rupak

of Organic Chemistry, of Science, Jadavpur,

Abstract : An efficient and Markovnikov hydration of alkenes achieved by a simple reaction borohydride in 1,2_dimethoxyethane.

Hydration synthesis. on

In

such

alcohol

of alkenes

principle,

reaction

can

depending

on

manner

demercurat addition

alkenes

ion’

of

is

the

As useful

a

in

anti -Markovni

kov

In

ml)

was

for

2h

a

added

to

reaction

was

reaction

mixture

filtered.

The pure

recently,

was

efficient

method

alkenes

produce

(1

at then was

a

solution

mmol) gel

room

g,

temperature

decomposed extracted

grade

with with

careful ether

product.

4659

and

reaction clean

in

been

till

dropwise

in

HF

addition was

of

mmol; at

254)

completion

extract

zinc

excellent

(2

(heated

binder,

for

of

regioselective

DME’

on activated

the

also

alcohols

borohydride

stirring

and

Me3SiCI-

reactions

the

furnished

without

under

anti-

acids

have

that

adsorbed

TLC

the

Lewis

surfacemediated

support

zinc

Markovnikov to

manner.

less-substituted of

uniformly (1

utilize

gel the

the

leads

CoC12-NaBH4,5

discovered

on silica

to

silica

to

have

regioselective oxymercuration-

for

of

bond

substituted

anti-Markovnikov

clean

general,

combinations

efforts we

procedure,

alkene

filtrate

In

in an anti-Markovnikov

continuing

in organic double

less

or

the

TiC14-PhCH2NC(Et)3-BH47

with

continued

for

importance.

very

the

Markovnikov

very

hydration

vacuum)

the

reactions

or

TiC14-NaBH4,4

our

general

under

the

DME

useful

carbinol

methods

various

of olefins

Saha

carbon-arbon

hydroboration-oxidation’

Recently,

transformations,*

borohydride

yields.

of

a

hand,

most

SnC14-NaBH4,3

hydration

part

synthetic

in of

synthetic

provides

and

to effect

substituted

hydration

great

other

e.g.

PhCH2N+(Et)3-6H46 reported

of

hydration.

borohydrides,

more

of

the

alkyl-substituted

realisation

alkenes

on

kov

mode

Thus,

of

and,

Markovni

leave

the

the

Manika

Indian Association for the Calcutta - 700 032, India.

is one of

unsymmetrical

produce

and

general procedure of regioselective antiproducing less-substituted alcohls has been of alkene on silica gel support with zinc

to alcohols

an

respectively.

hydration

Chakraborty

3

200°C

and

the

(TLC).

The

water,

and

evaporated

to

Hydration

Table 1

:

Entry

Alkene

of Alkenes

=CH2

Ph “>

0

5

=

Silica

Gel Supported

Zinc

Borohydride

Yield

Time(h)

Product a

0.5

CH3(CH2),CH20H

1

PhCH2CH20H

(80%Ic

PhCH(OH)CH3

(20%)

PhCH=CH2

;z>

with

(%Ib

95 85

+

1.5

PhCH(Me)CH20H

90

24

PhCH(OH)CH2Ph

70


H

0.5

I

85

Me 6

0.5

o”coMHe

21

a;;

+ a;

(70:30)’

80

h 7

(y;+

9

:I co ’

10

-aAll

’

70

a,”

mOH+

(55:45,cgo

&$5:251c

go

-_.- --

compounds

authentic and

+ a;(75:25)’

samples.

stereoisomers

identified

were b

All

was

yields estimated

by refer by

direct to ‘H

comparison

isolated

pure

NMR and

CC.

of

physical

products.

‘The

data

with

ratio

of

those regio-

of

4661

As

shown

regioselective

in

or

The

reactionsare

The

hydration

this

of

of

identical

and

of

zinc

and and

investigations

to

being

out.

carried

In

of

alcohols.

of

attractive borohydrides

sensitive

their

gel

side

and

is

does

is

other

also

produced

essential

whatever

be

clean

corresponding general,

is

other

than

the

regio-

clear

but

a

normal

observations

: (a]

and

reaction

to

Lewis

acids

will

find

high

an

and

will

make

methods

hydroborating

important

necessary

and

are

now

present for

less-substituted

reaction

this

condition,

reagent-system

and in

zinc

further

the

involving

agents2

of

methodology

mild

applications

sulfate,

Thus,

producing

neutral

yield

zinc

combination

efficient

other

hydration.

reaction-path,

alkenes

in

under

On the any

proceed.

are

provides of

existing or

to

of

borohydride

acetate,

A

alcohols.

6,7,8,9]

necessary

reaction.

zinc

process

is

promote

like

nature

gel

zinc

any

reaction

this

exact

the 3-7

to

(entries

agent

of

to

salts

simplicity,

and

lead

no

hydration

alternative

place

failed

this

silica

stereoselective

in

zinc

of

following

no oxidizing

not

for

the

procedural

strong

the in

very

the

not

(b)

with

mechanism

certainly,

give

products

yet

of

alone

the

the

combinations we believe,

systems

an of this

containing

functionalities.

We

Acknowledgement. Delhi

support

borohydride

borohydride

useful

methodology,

gel

anti-Markovnikov

any and

sodium

chloride

unravel

Moreover,

absence

system

borohydride

silica

zinc

not

use

borohydride

regioselective

is because

reagent

of

to

underwent

regioselectivity,

no side

process;

conclusion,

combination

and

excluded

this

zinc

zinc

borohydride

fast

alkenes

procedure

The

hydroboration

or

zinc

this-

yields.

reaction

be

on silica

gel

Replacement

the

(c)

condition silica

oxide

with

normal

by

varied

observed.

this

may

alkenes in

reaction;

hand,

were

mechanism

observed

high

reasonably

alcohols

hydroboration-oxidation

structurally

hydration in

alcohols

stereoisomeric

as

several

1,

anti-Merkovnikov

less-substituted excellent.

Table

[Grant

No.

are

02(355)]

pleased for

to

this

acknowledge

investigation.

financial R.C.

and

support M.S.

from

also

CUR,

thank

CSIR

fellowships.

References

and

Notes

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