M.-S. Yang et al. / Tetrahedron Letters 49 (2008) 253–256
255
EtO
Normal University, and National University of Singa-
pore for partial financial support of the work.
TMSCl
InCl3
OEt
Cl
TMSOEt
R
Si(OEt)3
Si
R
CHO
OTMS
OEt
Supplementary data
Supplementary data associated with this article can be
Si
H
or ClMe3Si-InCl3
O
ClMe3Si-InCl3
O
References and notes
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R
OEt
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-
R = H, CH2=CH-CH2
´
2004, 60, 1959; (c) Auge, J.; Lubin-Germain, N.; Uziel, J.
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Scheme 1. Possible mechanistic pathway for allylation–etherification
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and reductive etherification of aldehyde with functional silane.
Although the present limitation that only unsymmetrical
ethyl ethers were obtained in this reaction existed, we
believe the perspective versatile ethers could be prepared
by using different trialkyloxysilanes.
For the above allylation–etherification and reductive
etherification of silane, we proposed that they carried
out similar mechanism. A likely mechanistic pathway
for these transformations is shown in Scheme 1. It is rea-
sonable to assume that in situ formed silyl ether and
chlorosilane via the exchange reaction of TMSCl with
allyltriethoxysilane or triethoxysilane. And the catalyst
system (InCl3 in the presence of TMSCl) activates the
aldehyde toward the nucleophilic attack by the silyl
ether to give an intermediate, which undergoes a frag-
mentation to give an oxonium species.22 The oxonium
species undergoes reduction or allylation with the corres-
ponding silane reagent leading to the formation of the
product, homoallylether or ether.
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In summary, the InCl3 in the presence of TMSCl was
efficient catalyst for the synthesis of unsymmetrical
ethers by allylation–etherification and reductive etherifi-
cation of aldehydes with functional silanes, allyltriethoxy-
silane, and triethoxysilane. The catalyst system offers
significant advantages in its ease of preparation and
handling, and most importantly, in its ability to catalyze
the formation of unsymmetrical ethers from aromatic
aldehydes in almost quantitative yields directly. It is also
notable that it is a first example by using low reactive tri-
ethoxysilane and allyltriethoxysilane in the preparation
of versatile ethers via catalytic allylation–etherification
and reductive etherification, which would open new
entries to the synthesis of ethers and related compounds
by using functional silanes.
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This study was supported by the National Natural Sci-
ence Foundation of China (No. 20572114), Hangzhou