Introduction
<P>Sodium dithionite (also known as sodium hydrosulfite) is a versatile,
inexpensive, safe and readily available reagent, which has been
employed for more than 70 years. It has been used in biochemistry
for the reduction of a variety of coenzymes and enzymes, and in
organic synthesis to reduce several types of functional groups,
such as aldehydes, ketones, imines, pyrazine, vinyl sulfones, nitro
[
¹]
and azo groups,
[
²]
oximes,
[
³]
enones,
[
4]
quinones,
[
5]
and azides.
[
6]
It was also found to be an efficient
reagent for the reductive displacement of iodine
[
7]
and reductive coupling of benzylic
and allylic halides.
[
8]
It has been
also used as radical initiator to promote coupling of CF
3CHClBr
with 1,3,5-trimethoxybenzene,
[
9]
the
addition of 1-bromo-1-chloro-2,2,2-triuoroethane
to the terminal double bond of allylbenzenes,
[
¹0]
addition
reaction of peruoroalkyl iodides with allenes,
[
¹¹]
the reaction
of polyfluoroalkyl iodides with alkenes,
[
¹²]
addition
of dialkyl phosphonodifluoromethyl radical onto unsaturated ketones,
[
¹³]
fluoroalkylation
of porphyrins
[
¹4]
and vinyl
ethers.
[
¹5]
This reagent
is found to be a useful reagent in the intramolecular Marschalk cyclization
[
¹6]
and Claisen rearrangement.
[
¹7]
</P><P>Sodium dithionite is now commercially available, but can also
be prepared readily by the reaction of sodium bisulfite with zinc.
[
¹8]
It is obtained as a
white crystalline powder with a weak sulfurous odor. This compound
is stable under most conditions, but it will decompose in hot water
and in acid solutions.</P>
Scheme 1
