The Knoevenagel condensation reaction involves the nucleophilic addition of an active hydrogen compound to a carbonyl group, followed by a dehydration reaction to form an α,β-unsaturated enone. It is a modification of the aldol condensation and uses an active methylene compound and an aldehyde or ketone in the presence of a weak base such as pyridine. With malonic acid derivatives, the reaction product can undergo decarboxylation to form trans-2,4-pentadienoic acid. The Knoevenagel reaction is widely used in the synthesis of conjugated enones for various reactions.

2.  Knoevenagel condensation is 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
alpha, beta conjugated enone.
 Knoevenagel reaction is a modification of Aldol condensation
reaction.
 The active hydrogen compound used should be of the form
Z-CH2-Z or Z-CHR-Z where Z is an electron withdrawing
group.

3.  Eg: Diethyl malonate, Malonic acid and ethyl acetoacetate
H5C2OOC-CH2-COOC2H5
Diethyl malonate
HOOC-CH2-COOH
Malonic acid
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.

4.  The carbonyl group is an aldehyde or a ketone.
 Eg: Acetaldehyde (CH3CHO), Acetone (CH3CO CH3)
 The catalyst is usually a weakly basic amine.
 Eg: Pyridine (C5H 5N)

5. Knoevenagel condensation is 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
alpha, beta conjugated enone.

6. The condensation of carbon acid compounds with aldehydes to
afford α,β-unsaturated compounds.
The Doebner Modification, which is possible in the presence of
carboxylic acid groups, includes a pyridine-induced
decarboxylation

7.  Step:1: An enol intermediate is formed initially.

8.  Step:2: The enol formed reacts with aldehyde, and the
resulting aldol undergoes based induced elimination.

9.  With malonic compounds the reaction product can lose
a molecule of carbon dioxide in a subsequent step. The
base is pyridine. For example, the reaction product of
acrolein (allyl aldehyde) and malonic acid in pyridine is
trans-2,4-Pentadienoic acid with one carboxylic acid
group and not two.
Acrolein
Malonic acid
trans-2,4-Pentadienoic acid

10.  The Knoevenagel condensation is a key step in the
commercial production of the antimalarial drug
lumefantrine.
 Knoevenagal reaction is used in the synthesis of conjugated
enones which serve as key intermediates in various
reactions.
 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.