Studies on epoxides. Part I. α-Substituted epoxy-steroids

Abstract

The acid-catalysed opening of the epoxide ring in the eight stereoisomeric 5,6-epoxy-4-hydroxy- and 4,5-epoxy-6-hydroxy-cholestanes has been studied. Upon hydrobromic acid cleavage the 5α,6α-epoxides yielded diaxial bromohydrins, while the 5β,6β-epoxides gave a diequatorial bromohydrin or a mixture of diaxial and diequatorial bromohydrins, depending on the orientation of the substituent at C-4. With the exception of the cis-β-epoxy-alcohol, the remaining 4,5-epoxy-6-hydroxycholestanes yielded, under slightly acidic conditions, products resulting from cleavage of the C(4)–O bond. Both cis-epoxy-alcohols (5β,6β-epoxy-4β-hydroxy- and 4β,5β-epoxy-6β-hydroxy-cholestane) rearranged, to cholest-5-en-4-one and cholest-4-en-6-one, respectively. The implications of these reactions are discussed.