Knoevenagel condensation [SEP] named after
Knoevenagel condensation
The Knoevenagel condensation () reaction is an organic reaction named after Emil Knoevenagel. It is a modification of the aldol condensation.
A Knoevenagel condensation is a nucleophilic addition of an active hydrogen compound to a carbonyl group followed by a dehydration reaction in which a molecule of water is eliminated (hence "condensation"). The product is often an α,β-unsaturated ketone (a conjugated enone).
In this reaction the carbonyl group is an aldehyde or a ketone. The catalyst is usually a
Gewald reaction
The Gewald reaction is an organic reaction involving the condensation of a ketone (or aldehyde when R = H) with a α-cyanoester in the presence of elemental sulfur and base to give a poly-substituted 2-amino-thiophene.
The reaction is named after the German chemist Karl Gewald (born 1930).
Reaction mechanism.
The reaction mechanism of the Gewald reaction was elucidated 30 years after the reaction was discovered. The first step is a Knoevenagel condensation between the ketone (1) and the