Aldol Condensation

Overview

Aldol condensation is a reaction where an enol or enolate ion reacts with a carbonyl compound to form a β-hydroxyaldehyde or β-hydroxyketone.
This is followed by dehydration to give a conjugated enone.
Important for forming carbon-carbon bonds, used in many organic syntheses.

Aldol Reaction: Nucleophilic addition of a ketone enolate to an aldehyde.
Dehydration: Eliminates water or alcohol, may involve decarboxylation.
Two mechanisms:
- Strong base (e.g., potassium t-butoxide) in enolate mechanism.
- Acid-catalyzed enol mechanism.
Control Conditions: Kinetic vs. Thermodynamic control depending on the desired product.

Claisen-Schmidt Condensation: Reaction with an aromatic carbonyl lacking an alpha-hydrogen.
Knoevenagel Condensation: Base is an amine with an activated hydrogen compound.
Perkin Reaction: Aromatic aldehyde with an anhydride.
Claisen Condensation: Involves two esters.
Dieckmann Condensation: Involves two ester groups in the same molecule, yielding a cyclic molecule.
Henry Reaction: Aldehyde with an aliphatic nitro compound.
Robinson Annulation: Involves Michael reaction prior to aldol condensation.
Guerbet Reaction: Self-condensation of aldehyde formed in situ from alcohol.
Japp-Maitland Condensation: Water removed by nucleophilic displacement, not elimination.

Aldol condensation is often confused with aldol reaction, especially in biochemistry, although they are distinct processes.
Named reactions like Claisen-Schmidt have unique historical backgrounds.