Direct Conversion of Trimethylsilyl and Tetrahydropyranyl Ethers into Esters with Acid Chlorides in the Presence of Montmorillonite K-10

Article abstract of DOI:10.1081/SCC-120026313

A simple method is described for an efficient conversion of variety of trimethylsilyl (TMS) and tetrahydropyranyl (THP) ethers into their corresponding esters with acid chlorides in the presence of montmorillonite K-10.

Full text of DOI:10.1081/SCC-120026313

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Õ
SYNTHETIC COMMUNICATIONS
Vol. 33, No. 22, pp. 3907–3912, 2003
Direct Conversion of Trimethylsilyl and
Tetrahydropyranyl Ethers into Esters with
Acid Chlorides in the Presence of
Montmorillonite K-10
Barahman Movassagh* and Kobra Atrak
Department of Chemistry,
K. N. Toosi University of Technology, Tehran, Iran
ABSTRACT
A simple method is described for an efficient conversion of variety
of trimethylsilyl (TMS) and tetrahydropyranyl (THP) ethers into
their corresponding esters with acid chlorides in the presence of
montmorillonite K-10.
Esters are common intermediates in natural product chemistry due to
their stability and accessibility for easy interconversion. The traditional
[1]
preparations use acid and alcohol in the presence of classic acids
*
Correspondence: Barahman Movassagh, Department of Chemistry, K. N.
Toosi University of Technology, Tehran 15418, Iran; E-mail: movassagh@
kntu.ac.ir.
3
907
DOI: 10.1081/SCC-120026313
Copyright & 2003 by Marcel Dekker, Inc.
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908
Movassagh and Atrak
which are corrosive in nature. Further modifications use alcohols and acid
chlorides.
[
2–6]
[7]
Other routes such as transesterification, alkylation of car-
[8]
[9]
boxylate anions, and cleavage of ethers have also been used. However,
just a few reports are available dealing with the conversion of trimethylsilyl
and tetrahydropyranyl ethers into the corresponding esters. In a recent
report, a variety of TMS and THP ethers were converted to the corre-
sponding acetates and benzoates with acetic and benzoic anhydrides in
[
10]
[
10b]
the presence of Bi(III) salts in refluxing acetonitrile.
Montmorillonite clays, a class of inexpensive and noncorrosive solid
acids, have been used as efficient catalysts for a wide variety of organic
[
11]
reactions. Recently, we introduced two convenient one-step procedures
for the deprotection -acetylation of TMS ethers with acetic anhydride
[
10d]
using montmorillonite K-10.
In view of environmental, practical,
and economical demands and to explore the generality and scope of
montmorillonite K-10 catalyzed esterification, this article describes a
simple, efficient, and mild one-pot method to transform different classes
of TMS and THP ethers to the corresponding esters with acid chlorides at
room temperature using montmorillonite K-10 as a mild heterogeneous
catalyst (Sch. 1).
The reactions were performed with equimolar amounts of the ethers
and acid chlorides in the presence of the clay in chloroform at room
temperature. The representative examples illustrating the conversion of
TMS ethers into the corresponding esters are listed in Table 1. The results
clearly show the need for longer reaction times for silylated phenols,
giving the esters also with lower yield.
Table 2 shows the results obtained for THP ethers. The reaction
of the THP ether of benzyl alcohol with acetyl and propionyl chlorides
gave the corresponding esters in 0.5 h, whereas the reaction of the same
ether with benzoyl chloride was rather slow (3 h). THP ethers of primary
and secondary alcohols gave the esters with much better results than the
THP ether of tert-butanol (Table 2, Entry 14).
In summary, the present method describes a simple, mild, and efficient
procedure for one-pot transformation of TMS and THP ethers to the
corresponding esters in high yield. In addition, easy work-up, availability,
and nontoxicity of the catalyst are notable advantages of this method.
ROTMS
mont. K-10
+
R'COCl
ROCOR'
CHCl , r.t.
ROTHP
3
Scheme 1.

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Conversion of TMS and THP Ethers
3909

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2003 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
3
910
Movassagh and Atrak

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Conversion of TMS and THP Ethers
EXPERIMENTAL
3911
Infrared spectra were obtained using a Shimadzu IR-408 instrument.
H NMR spectra were recorded on a Jeol JNM-EX90A. Products were
1
characterized by comparison of their physical data, IR, and NMR
spectra with those reported in the literature.
General Procedure for the Conversion of TMS Ethers into
Their Corresponding Esters
To a stirred suspension of TMS ether (1 mmol), dry chloroform
6 mL), and montmorillonite K-10 (250 mg), acid chloride (1.2 mmol)
(
was added dropwise. The mixture was stirred at room temperature for
the length of time indicated in Table 1. The progress of the reaction was
monitored by TLC. After completion of the reaction, the catalyst was
removed by filteration and the filtrate was evaporated. The resulting
crude product was purified by preparative TLC (silica gel; eluent, dichlor-
omethane/petroleum ether, 5:1) to afford the ester.
General Procedure for the Conversion of THP Ethers into
Their Corresponding Esters
To a stirred solution of THP ether (1 mmol) in dry chloroform (6 mL),
montmorillonite K-10 (250 mg) was added. Acid chloride (1.2 mmol) was
added to the heterogeneous mixture and stirring at room temperature
continued for the appropriate time (Table 2). The contents were filtered
and the filtrate was evaporated. The resulting crude product was purified
by preparative TLC (silica gel; eluent, dichloromethane/petroleum ether,
5:1 or n-hexane/ethyl acetate, 5:1) to obtain the ester.
ACKNOWLEDGMENT
The authors are grateful to K. N. Toosi University of Technology
Research Council for financial assistance of this project.

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912
Movassagh and Atrak
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1
Received in the USA June 2, 2003

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