A modified phase-transfer catalysed enantioselective epoxidation of estra-Δ5(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 α/β epoxide up to 7:1.
Keywords: Mifepristone, estra-Δ5(10),9(11)-diene, cinchona alkaloids, chiral ammonium salts
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