title: Synthesis of 3-hydroxy-, 3-chloro-, and 3-methoxy-3-cephems from penicillins via 4-dithio-2-azetidinone intermediates.
mesh_terms: D001384:Azetidines; D001385:Azetines; D002511:Cephalosporins / Q000138:chemical synthesis*; D002713:Chlorine; D006900:Hydroxylation; D008745:Methylation; D010406:Penicillins
chemical_list: D001384:Azetidines; D001385:Azetines; D002511:Cephalosporins; D010406:Penicillins; D002713:Chlorine