A Synthesis of Cephamycins from Cephalosporins and Related Reactions

Abstract

The sulfinamides 3 were transformed to sulfenimines 4 by treatment with thionyl chloride and a weak base such as quinoline (or triethylamine). The sulfenimines 4 were methoxylated with lithium methoxide to give 7α-methoxysulfenamides 5, which were directly acylated with an acyl chloride to furnish cephamycin derivatives 6. There was a major difference between the acylation of 7α-methoxysulfenamides 5 and that of the 7α-H derivatives 7. Reduction of the imines 4a with metal hydrides gave 7β-sulfenaminocephalosporins 12 together with a small amount of the 7α-isomers 13. The synthetic sequence 4a→12→14 provides a useful method for the isomerization of 7α-aminocephalosporins 17 to the corresponding 7β-isomers 18.