Synthesis of 3-Hydroxycephems from Penicillin G through Cyclization of Chlorinated 4-(Phenylsulfonylthio)-2-azetidinones Promoted by a BiCl3/Sn or TiCl4/Sn Bimetal Redox System

Abstract

Abstract A novel access to 3-hydroxycephems was attained from penicillin G via the C=C bond cleavage of 1-(1-alkoxycarbonyl-2-chloromethyl-2-propenyl)-4-(phenylsulfonylthio)-2-azetidinones by successive treatment with RuCl3/HIO4 and HIO4/CuSO4 and reductive cyclization of 1-(1-alkoxycarbonyl-3-chloro-2-hydroxy-1-propenyl)-4-(phenylsulfonylthio)-2-azetidinones on treatment with a newly devised BiCl3/Sn or TiCl4/Sn bimetal redox couple in DMF containing pyridine.