Reduction of 6α-alkyl-6β-isocyanopenicillanates by tri-n-butyltin hydride. A stereoselective synthesis of 6β-alkylpenicillanates

Abstract

Summary 6β-Benzyl-, 6β-(1-hydroxy-1-methylethyl)-, 6β-methoxycarbonylmethyl-, and 6β-(2-methoxycarbonylethyl)-penicillanates (5)–(8) have been prepared stereoselectively, and in good yield, by tri-n-butyltin hydride reduction of the corresponding 6α-alkyl-6β-isocyanopenicillanates (1)–(4); similarly 6,6-dibromopenicillanate (12) has been reduced to give a mixture of 6β- and 6α-bromopenicillanates (13) and (14) in the ratio of 85 : 15, respectively.