D-Homo-steroids. Part II. A study of the mechanism of base-catalysed D-homoannulation of 3β-17α-dihydroxy-5α-pregnan-20-one

Abstract

D-Homoannulation of 3β,17α-dihydroxy-5α-pregnan-20-one (I) with five different base–solvent systems afforded wide variations in rates of reaction. The products were the epimeric 17a-hydroxy-17a-methyl-17-ketones (II) and (IV), derived exclusively from migration of the C(13)–C(17) bond. Each mixture tended eventually towards an equilibrated mixture of (II) and (IV), but the order in which these products were formed initially depended upon the particular base and solvent employed. Earlier theories concerning the mechanisms of these reactions are discussed and elaborated with some modification in the light of the new results.