Enantioselective Protonation of Enol Esters with Bifunctional Phosphonium/Thiourea Catalysts.

Bifunctional phosphonium/thioureas derived from tert-leucine behaved as highly selective catalysts for enantioselective protonation of enol esters, providing α-chiral ketones in yields of up to 99% with high enantioselectivities (up to 98.5:1.5 er).