Activation of mixed carboxylic α-bromotoluoyl anhydrides by silver tetraflouroborate. Synthesis of ester and thiol esters

Tetrahedron Letters,Vo1.28,No.40,pp Printed in Great Britain

ACTIVATION

OF MIXED CARBOXYLIC

TETRAFLUOROBORATE.

Satoshi Fukuoka,+ Department

4711-4712,1987

a-BROMOTOLUOYL

SYNTHESIS

Seiji Takimoto,

of Chemistry,

Faculty

ANHYDRIDES

BY SILVER

OF ESTERS AND THIOL ESTERS

Tsutomu

Katsuki,*

of Science,

Fukuoka

oo40-4039/87 $3.00 + .OO Perqamon Journals Ltd.

and Masaru Yamaguchi

Kyushu University

33, Higashi-ku,

812, Japan

Sumnary: Mixed carboxylic a-bromotoluoyl anhydrides were activated by silver tetrafluoroborate through intramolecular cyclization and reacted with alcohols or thiols giving the corresponding esters or thiol esters in good yileds with the elimination of phthalide. We previously

reported

and o-bromotoluoyl

bromide

a new type of mixed anhydrides (l),l) which on heating

(2) prepared

from carboxylic

acids

at 80-145

OC in benzene or --N,N,N',N'in good yields with the elimination of

’

tetramethylurea with alcohols gave carboxylic esters 2) phthalide. In this communication are described a new, non-thermal activation of this unique mixed anhydrides and its application to the synthesis of esters 31 and thiol esters. 41 In a search for effective as a general

additives

and strong acylating

which make the anhydrides

agents, a stoichiometric

has been found to be the most satisfactory dichloromethane or thiols

or acetonitrile

led to the formation

results obtained

at room temperature,

(DME) throughout

It is noteworthy

Activation

the activation

and esterification

Cyclized

active intermediates

and the facile

for the reaction

to promote

The experimental pentanethioate.

bromide

of alcohols

however,

processes

species

elimination

of methyl

(3) are postulated of phthalide

by the preparation

of alcohols was carried

as the

(41 from them is

of S-isopropyl

Z-methyl-

out in the same manner.

(1, 75 ~1, 0.5 mmol) was added to a stirred mixture of Zthrough

(70 ~1, 0.5 mnol),

Celite, concentrated,

AgBf4 R

and ether

(0.8 ml).

and diluted with acetonitrile (92 mg, 0.5 mmoll and, after

>

I

Br Et3N

>

COBr BF4) (1)

The

the use

gave the best

in the esterification

To this solution were added silver tetrafluoroborate

, ’ d ’

in

property.

is exemplified

was filtered

Br RCOOH +

cationic

acid (63 ~1, 0.5 mnol), triethylamine

After 1 h, the mixture (0.8 ml).

procedure

The acylation

cl-Bromo-o-toluoyl methylpentanoic

their acyl-transfer

addition

of benzenethiol,

was detected

hydrogen meso-2,4_dimethylglutarate.

considered

very rapidly

esters or thiol esters in good yields.

For the acylation

that no epimerization

of 2 occurred

and the subsequent

of the corresponding

are shown in Table 1.

of dimethoxyethane result.

one.

usable under mild conditions

amount of silver tetrafluoroborate

(21

(3)

4711

(4)

4712

Reaction

Table 1.

of Mixed Anhydrides

(2) Activated

by Silver Tetrafluoroborate

with Alcohols

and Thiols Time(min1

Yieldb' of Ester or Thiol Ester

a)

R in RCOOH

R'OH or R'SH'

Solvent

CH3CH2CH2

(CH312CHOH

CH2C12

8

84(67)

CH3CH2CH2tCH3)CH

CH3CH20H

CH2C12

10

81(721

CH3CH2CH2(CH3lCH

(CH312CHOH

CH2C12

30

85(75)

(CH3)3C

cycle-C6Hl,0H

CH2C12

15

94

(CH313C

C6H50H

CH2C12

1

77(69)

(CH312CHOH

CH2C12

3

(621

meso-CH30COCH(CH3)CH2(CH3)CH

(CH~)~CHOH

CH2C12

40

CH3CH2CH2

(CH313CSH

CH2C12

4

94(74)

CH3CH2CH2(CH3lCH

CH3CH2SH

CH3CN

5

(83)

CH3CH2CH2(CH31CH

(CH3)*CHSH

CH3CN

10

83(801

(CH3)3C

(CH313CSH

CH3CN

15

(81)

(CH313C

C6H5SH

DME

15

82d1

meso-CH30COCH(CH31CH2(CH31CH

(CH313CSH

CH2C12

5

72')

'gH5

a) Reaction

time required

GLPC by comparing parentheses. mens.

for alcoholysis

with appropriate

All the products

cl No epimerization

or thiolysis

internal

standards,

were identified

was detected

of 2.

84"

b) Yields were determined

by

Isolated yields were given in

by 'H-NMR by comparing

by GLPC analysis.

with authentic

speci-

d) The reaction were carried

out at -10 "C. 3 min, Z-propanethiol ture, diluted

(46 ~1, 0.5 mmol).

with pentane

(2 ml), and filtered.

aqueous sodium hydrogencarbonate and concentrated

The mixture

was stirred for 10 min at room tempera-

The filtrate

and water successively,

to a residue which was distilled

was washed with saturated

dried over anhydrous

to afford S-isopropyl

sodium sulfate,

2-methylpentanethioate

in 80% yield. Further

studies

on the application

of this type of anhydrides

are in progress.

References t Present

address;

Takamatsu

Goverment

Industrial

Research

Institute,

Shikoku,

Hananomiya

2-3-3,

761

1) W. Davies and W. H. Perkin,

Jr., J. Chem. Sot.,

21 H. Horimoto,

S. Takimoto,

T. Katsuki,

31 For a review

of esterification,

1922. 2202.

and M. Yamaguchi,

see E. Haslum,

Chem. Lett., 1979, 145.

Tetrahedron,

36, 2409 (19801 and references

cited therein. 41 Examples

of mild preparation

of thiol esters:

16, 244 (19771; bl Y. Kawanami,

Y. Dainobu,

a) H.-J. Gais, Angew. Chem.

J. Inanaga,

T. Katsuki,

Bull. Chem. Sot. Jpn., 54, 943 (1981); cl T. Imamoto, M. Kodera, Synthesis,

1982, 134. and references

cited therein.

(Received in Japan 13 June 1987)

Int. Ed. Engl.,

and M. Yamaguchi,

and M. Yokoyama,