Feist–Benary synthesis

The first step in the ring synthesis is related to the Knoevenagel condensation.

In the second step the enolate displaces an alkyl halogen in a nucleophilic aliphatic substitution.

In place of α-haloketones, propargyl sulfonium salts can be used to alkylate the diketone.

[2] Another modification is the enantioselective interrupted Feist-Benary reaction[3] with a chiral auxiliary based on the cinchona alkaloid quinine based in the presence of proton sponge to the hydroxydihydrofuran.

The alkaloid is protonated throughout the reaction and transfers its chirality by interaction of the acidic ammonium hydrogen with the dicarbonyl group of ethyl bromopyruvate in a 5-membered transition state.