A New Protocol for a Regioselective Aldol Condensation as an Alternative Convenient Synthesis of β-Ketols and α,β-Unsaturated Ketones

Abstract

A general and convenient synthesis of β-ketols and α,β-alkenones has been achieved by a Knoevenagel condensation of a β-ketoacid with an aldehyde in aqueous medium. Saponification of a β-ketoester by an aqueous KOH 10% solution gives the potassium salt of the β-ketoacid, which is condensed in situ with an aldehyde at pH 7.8−8.0, at 60 °C for 5−6 h. The intermediate β-ketocarboxylate is smoothly decarboxylated in the reaction medium, giving the β-ketol in high yield (75−90%). Acidification of the reaction mixture at pH 1 and heating at 70 °C under vigorous stirring for 6 h, leads directly to the corresponding α,β-unsaturated ketone in good yield (65−75%).