Introduction
<P>Lewis acids are very useful reagents in organic synthesis. The
classical Lewis acids currently used include BF
3
·ΟEt
2, ZnCl
2,
SnCl
2, TiCl
4 and many others. Nickel chloride
can be also added to this list. NiCl
2 is a mild Lewis
acid that promotes a wide variety of organic transformations in
aqueous medium or organic solvent and may be used either catalytically
or stoichiometrically. NiCl
2 was also used in a key step
in the synthesis of bibenzopyran-4-ol,
[
1]
tetrahydrodicranenone
B
[
2]
and Allopumiliotoxins.
[
3]
NiCl
2 is a
selective reductive agent when used with hydrides such as LiAlH
4 and
NaBH
4. In fact, the mixture of NiCl
2 and NaBH
4 is
used to prepare nickel boride,
[
4]
a
reducing agent for many functional groups: azide,
[
5]
nitrile,
[
6]
NO
bond,
[
7]
alkene
[
8]
and
haloalkane.
[
9]
NiCl
2 was
used in the regioselective rearrangement of dienols,
[
10]
ring-opening of epoxide,
[
11]
nickel(II)/chromium(II)
chloride-mediated addition to aldehydes or ketones,
[
2]
[
3]
Suzuki cross-coupling,
[
12]
Biginelli reaction,
[
13]
reductive Heck-like reactions,
[
14]
nickel-catalyzed cross-coupling
reaction of Grignard reagents
[
15]
and
homo-coupling reactions.
[
16]
</P>
