Phase-Transfer Catalysed Enantioselective Epoxidation of Estra-Δ5(10),9(11)-diene Using Chiral Ammonium Salts Derived from Cinchona Alkaloids

A modified phase-transfer catalysed enantioselective epoxidation of estra-Delta(5(10),9(11))-diene, an important intermediate of anti-early pregnancy drug mifepristone 1, have been determined and investigated. Eight chiral ammonium salts (PTC A-H), used as phase-transfer catalysts, have been synthesized from cinchona alkaloids. Among them, PTC G and PTC H have exhibited satisfying catalytic activity to improve the ratio of alpha/beta epoxide up to 7:1.