L. C. Wieland et al. / Tetrahedron Letters 43 (2002) 4597–4600
4599
1
carbonyl compound was detected by H NMR spec-
troscopy of the crude product. This observation sug-
gests that bismuth triflate catalyzed allylation is
significantly faster than deprotection of acetal by any
water present in the solvent. This is a significant advan-
tage over other methods that require the use of strictly
anhydrous conditions. When the allylation of benzalde-
hyde dimethyl acetal (entry 1) was done neat, in addi-
tion to the desired product, considerable amounts of
impurities were formed. The procedure works well with
a wide variety of acetals including acetals derived from
conjugated aldehydes (entry 6). It has been reported
that with TiCl4 as the activator, the reaction of cin-
namaldehyde dimethyl acetal with allyltrimethylsilane
gave only the diallylated product.2 Even at low temper-
atures (−78°C), the monoallylated product was not
formed. Similar results were obtained when allylation
of cinnamaldehyde dimethylacetal was carried out
using allyl bromide in the presence of AlBr3.5 In con-
trast, we did not observe any diallylated product using
bismuth triflate as the catalyst and the monoallylated
product was obtained in good yields in all cases.
In summary, this work demonstrates a new method for
high-yielding allylation of acetals using catalytic
amounts of Bi(OTf)3. Advantages of this method
include fast reaction rates and the use of a Lewis acid
that is highly catalytic in nature, is relatively inexpen-
sive, non-toxic and insensitive to small amounts of air
and moisture.
Acknowledgements
The authors wish to acknowledge funding by the
National Science Foundation (RUI grant). R.M. would
also like to acknowledge The Camille and Henry Drey-
fus Foundation for a research award. We would also
like to thank Professor Jacques Dubac, Universite Paul-
Sabatier, France for useful discussions.
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1
SM was present after 5 h. However H NMR analysis
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