TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 5309–5311
One-step conversion of silyl/THP ethers into the
corresponding acetates
Kusum L. Chandra, P. Saravanan and Vinod K. Singh*
Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India
Received 25 September 2000; revised 22 May 2001; accepted 1 June 2001
Abstract—A variety of silyl and THP ethers were directly converted into the corresponding acetates using acetic anhydride in the
presence of a catalytic amount of Cu(OTf)2 in CH2Cl2. It was observed that MEM ethers could also be cleaved under the same
conditions. The reaction was also studied with other Lewis acids. © 2001 Elsevier Science Ltd. All rights reserved.
The acylation of alcohols is a useful transformation in
day-to-day synthetic organic chemistry. Although there
are several methods for conversion of alcohols into
acetates under acidic and basic conditions,1 methods
for direct conversion of silyl/THP ethers into acetates
are limited, and even those suffer from serious draw-
backs. For example, the acetyl bromide/tin(II) bromide
combination has been used for direct conversion of silyl
ethers into acetates, but benzyl ethers are also cleaved
under these conditions.2 The FeCl3/Ac2O method also
suffers from similar drawbacks where benzyl, methyl,
and other ethers are also acylated.3 Similarly, conver-
sion of tetrahydropyranyl (THP) ethers directly into
acetates using AcOH/AcCl4 and TiCl4/Ac2O5 is known.
These conditions are harsh and sensitive groups such as
acetonides are also acylated under the reaction condi-
tions. While working on the synthesis of (−)-carbovir,6
we observed that a t-butyldimethylsilyl (TBDMS) ether
was directly converted into an acetate with Ac2O in the
presence of a catalytic amount of Cu(OTf)2.7 We also
observed that the method is mild and simple and that
several silyl ethers were selectively acylated. The reac-
tion was also extended to the conversion of THP ethers
into acetates, and details are described in this paper.
respectively. Other Lewis acids were not satisfactory at
all. For example, ZnCl2 and BF3·OEt2, even in stoichio-
metric amounts, gave lower yields (56 and 12% yield,
respectively) of the acetate. FeCl3 and SnCl4 did not
give a clean reaction. The conversion of the above
TBDMS ether into the acetate in the presence of
Cu(OTf)2 was also studied in several solvents such as
CH2Cl2 (2.5 h, 75% yield), ether (24 h, 25% yield),
MeCN (3 h, 51% yield), MeNO2 (2.5 h, 64% yield),
benzene (3.5 h, 40% yield). From these results, it was
concluded that CH2Cl2 was the best solvent for this
reaction. It was further observed that the trimethylsilyl
(TMS) and tetrahydropyranyl (THP) ethers of a-
methylbenzyl alcohol could also be converted into
acetates by using acetic anhydride in the presence of 5
mol% of Cu(OTf)2 at room temperature (entries 2 and
3). In order to extend the scope of this reaction, a
variety of silyl and THP ethers were prepared and used
for their conversion into acetates (Table 1).
It was observed that methyl and benzyl ethers, which
are cleaved with FeCl3/Ac2O,3 are unaffected under the
present conditions (entries 12 and 21). The other inter-
esting part of the reaction was that the acetonide group
remained intact during the conversion of the TBDMS
ether into an acetate group (entry 21). Allylic silyl
ethers (entries 7 and 29) gave clean acetate products
only when the reaction was carried out in the absence
of solvent at lower temperature. It was observed that a
primary TBDMS ether can be deprotected in preference
to a secondary TBDMS ether with reasonable success
(entry 24). The phenolic TBDMS ether remains un-
affected under the above conditions (entry 25). It was
also observed that a TBDMS ether can be converted
into an acetate in the presence of a t-butyldiphenylsilyl
At the outset, a-methylbenzyl alcohol was protected as
the TBDMS ether and its conversion into an acetate
(entry 1) was studied with Lewis acids such as
Cu(OTf)2, Sn(OTf)2, ZnCl2, BF3·OEt2, FeCl3, and
SnCl4 in CH2Cl2 at room temperature (rt). It was
observed that a catalytic amount (5 mol%) of Cu(OTf)2
or Sn(OTf)2 efficiently converted the TBDMS ether into
the corresponding acetate in 2–3 h in 75 and 70% yield,
* Corresponding author. E-mail: vinodks@iitk.ac.in
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