A study of the Henbest reduction: the preparation of 3α-hydroxy-5α- and 3β-hydroxy-5β-steroids

Abstract

The reduction of 3-oxo-steroids by a solution of chloroiridic acid and trimethyl phosphite in 90% aqueous propan-2-ol (Henbest reduction) gives axial alcohols in the 5α- or 5β-series and is selective for 3-oxo-groups. Oxo-functions at C-6, C-11, C-12, C-17, and C-20 do not react. This method of reduction has been used as the key step in the synthesis of the ‘allo-tetrahydro’ metabolites of several steroid hormones, and related compounds.