Alkylated steroids. Part 4. An unusual Favorskii rearrangement

Abstract

Favorskii rearrangement of the mixed 17ξ-bromo-16α-methyl-20-oxo-5α-pregn-9(11)-en-3β-yl acetates (5) and (6)(9 : 1) gives methyl 3β-hydroxy-16α,17α-dimethyl-5α-androst-9(11)-ene-17-carboxylate (7) and methyl 3β-hydroxy-16α-methyl-5α-pregn-9(11)-en-21-oate (9) as the major components. Only a small amount of the isomeric 16α,17β-dimethyl-17-carboxylate (8) is formed. The structures of the esters (7) and (9) are confirmed by synthesis, and an explanation for the unexpected formation of (9) is advanced.