Hunsdiecker condensation

What is Hunsdiecker condensation?

In 1942, Hunsdiecker reported a reaction that enables the synthesis of 2,3-disubstituted cyclopentenones. The reaction involves an intramolecular condensation of 1,4-diketone (or γ-dicarbonyl compounds) with a base.

Hunsdiecker condensation - general reaction scheme
Hunsdiecker condensation

When 2-acetyl ketone is treated with a base, it can form two possible cyclopentenones: 2-alkyl-3-methyl cyclopentenone and 3-alkyl cyclopentenone. However, only the former has been reported as the isolated product. This is because the intramolecular condensation occurs via a reversible aldol condensation, and the transition state leading to the formation of 2-alkyl-3-methyl cyclopentenone is more stable  compared to that needed to give 3-alkyl cyclopentenone.

This reaction has been modified to occur under milder conditions using K2CO3/methanol.