Iodine-catalysed allylation of aldehydes with allyltrimethylsilane

Article abstract of DOI:10.1016/S0040-4039(02)00439-2

Iodine efficiently catalyses the allylation of both aromatic and aliphatic aldehydes with allyltrimethylsilane in acetonitrile at 0°C to afford the corresponding homoallyl alcohols in high yields in a short reaction time.

Full text of DOI:10.1016/S0040-4039(02)00439-2

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 3783–3784
†
Iodine-catalysed allylation of aldehydes with allyltrimethylsilane
J. S. Yadav,* Pratap K. Chand and S. Anjaneyulu
Indian Institute of Chemical Technology, Hyderabad 500 007, India
Received 22 August 2001; revised 18 February 2002; accepted 28 February 2002
Abstract—Iodine efficiently catalyses the allylation of both aromatic and aliphatic aldehydes with allyltrimethylsilane in
acetonitrile at 0°C to afford the corresponding homoallyl alcohols in high yields in a short reaction time. © 2002 Elsevier Science
Ltd. All rights reserved.
Allylation of aldehydes with allyltrialkylsilanes is one of
The reactions proceeded smoothly at 0°C with high
selectivity. The products were isolated in high yields
after a short reaction time (1 min). The generality of
this reaction is evident from the results summarised in
Table 1 which shows that a variety of aromatic and
aliphatic aldehydes are converted into the correspond-
ing homoallyl alcohols in high yields. The method does
not involve anhydrous solvents or stringent reaction
conditions and no additives or acidic promoters are
required. Acetonitrile is the solvent of choice giving the
best results. The method has the advantages of using
inexpensive reagents, greater selectivity, operational
simplicity, improved yields, enhanced rates and simple
experimental work up procedures.
the most powerful CꢀC bond forming reactions in
1
organic synthesis. Generally, strong Lewis acids such
as TiCl , BF –OEt , NbCl and SnCl were known to
4
3
2
5
4
catalyse these reactions. Recently, several metal
2
triflates such as Sc(OTf) , Yb(OTf) , Zr(OTf) and
3
3
4
Hf(OTf) were found to be effective for this transfor-
4
mation. But in most of the cases either a long reaction
time or drastic reaction conditions were employed.
However, many of these Lewis acids are moisture sensi-
tive and metal triflates are highly expensive. Therefore,
the development of new reagents with greater efficiency,
convenient procedures and delivering better yields is of
interest.
In continuation of our interest in the applications of
iodine for various transformations, we herein report a
As to the role of iodine, it could be reacting with the
formation of trimethylsilyl iodide, indeed this process is
3
mild convenient and rapid method using iodine as an
efficient catalyst for allylation of both aromatic and
aliphatic aldehydes with allyltrimethylsilane using a
catalytic amount of elemental iodine (Scheme 1). The
treatment of benzaldehyde with allyltrimethylsilane in
the presence of 0.2 equiv. of iodine in acetonitrile
afforded the corresponding homoallyl alcohol in 90%
yield. Similarly several aliphatic and aromatic alde-
hydes reacted well at 0°C in acetonitrile to give the
corresponding homoallyl alcohols in excellent yields.
4a
known, and it may be that it is the trimethylsilyl
iodide which catalyses these reactions. To test this
hypothesis, we carried out the reaction with various
aliphatic and aromatic aldehydes and allyltrimethyl-
silane in the presence of trimethylsilyl iodide (0.2
equiv.) under otherwise identical conditions. The prod-
ucts obtained were identical to those obtained when
iodine was employed. A comparable catalysis of the
reaction between allylsilanes and acetals by trimethyl-
4b
silyl iodide has been reported.
In conclusion, iodine is found to be a superior, efficient
catalyst for the allylation of various aldehydes with
allyltrimethylsilane under very mild and convenient
conditions. The present procedure provides a novel,
efficient and general methodology for the preparation
of homoallyl alcohols in high yields. The procedure is
very simple, quick and is one which may find use in
organic synthesis.
Scheme 1.
*
Corresponding author.
†
IICT Communication No. 4617.
0
040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)00439-2

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784
J. S. Yada6 et al. / Tetrahedron Letters 43 (2002) 3783–3784
Table 1. Conversion of aldehydes into homoallyl alcohols
Typical procedure: To a stirred mixture of aldehyde (a,
.106 g, 1 equiv.) and allyltrimethylsilane (0.19 ml, 1.2
0
equiv.) in dry acetonitrile at 0°C, iodine (0.05 g, 0.2
equiv.) was added. After 50 s the resulting mixture was
quenched with aqueous sodium thiosulphate and
extracted with diethyl ether (3×10 ml). The combined
organic layers were dried over anhydrous sodium sul-
phate, and the solvent was evaporated under reduced
pressure. The residue was purified by flash chromato-
graphy on silica gel (Merck, finer than 200-mesh, hex-
ane/ethyl acetate, 4:1) to afford pure product, charac-
1
terised by H NMR and mass spectroscopy.
Acknowledgements
P.K.C. and S.A. thank CSIR, New Delhi for the award
of fellowships.
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