Knoevenagel condensation

Knoevenagel condensation
Named after	Emil Knoevenagel
Reaction type	Coupling reaction
Identifiers
Organic Chemistry Portal	knoevenagel-condensation
RSC ontology ID	RXNO:0000044

The Knoevenagel condensation (pronounced [ˈknøːvənaːɡl̩]) 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 αβ-unsaturated ketone (a conjugated enone).

In this reaction the carbonyl group is an aldehyde or a ketone. The catalyst is usually a weakly basic amine. The active hydrogen component has the form

where Z is an electron withdrawing functional group. Z must be powerful enough to facilitate deprotonation to the enolate ion even with a mild base. Using a strong base in this reaction would induce self-condensation of the aldehyde or ketone.

The Hantzsch pyridine synthesis, the Gewald reaction and the Feist–Benary furan synthesis all contain a Knoevenagel reaction step. The reaction also led to the discovery of CS gas.

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