Everything about The Gewald Reaction totally explained
The
Gewald reaction is an
organic reaction involving the
condensation of a
ketone (or
aldehyde when R
2 = H) with a α-cyanoester in the presence of elemental
sulfur and base to give a poly-substituted 2-amino-
thiophene.
Reaction mechanism
The reaction mechanism of the Gewald reaction has only recently been elucidated. The first step is a
Knoevenagel condensation between the ketone (
1) and the α-cyanoester (
2) to produce the stable intermediate
3. The mechanism of the addition of the elemental sulfur is unknown. It is postulated to proceed through intermediate
4. Cyclization and
tautomerization will produce the desired product (
6).
Variations
In one variation of the Gewald reaction a
3-Acetyl-2-aminothiophene is synthesized starting from a
dithiane (an adduct of sulfur and
acetone) and the sodium salt of
cyanoacetone which in itself is very unstable :
Further Information
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