Introduction
<P>Recently, indium tribromide has received increasing attention as a novel type of
water-tolerant green Lewis acid catalyst for organic synthesis with highly chemo-,
regio- and stereoselective results.
[
1]
Compared to conventional Lewis acids, it has advantages of water stability, recyclability,
operational simplicity, strong tolerance to oxygen- and nitrogen-containing reaction
substrates and functional groups, and it can often be used in just catalytic amounts.
This catalyst promotes various transformations including alknylation of aldehydes
and
N,O-acetals,
[
2]
Michael addition,
[
3]
synthesis of 1,3-dioxane derivatives,
[
4]
conversion of oxiranes to thiiranes,
[
5]
sulfonation of indoles,
[
6]
alkynylation of acid chorides
[
7]
and synthesis of 2-halo-1,3-dienes.
[
8]
</P><P>Indium tribromide is conveniently prepared by heating metallic indium in a
current of nitrogen and bromine,
[
9]
and is now also commercially available.</P>
