Facial selectivity in the hydroboration of androst-4-enes

Abstract

In the absence of an allylic hydroxy group, the stereochemistry of hydroboration of an androst-4-ene is determined by the presence and stereochemistry of the C-10 methyl group. Allylic hydroxy groups at C-3 direct the hydroboration/oxidation to the anti-face. In the case of the 3α-alcohol, this effect is in opposition to the normal hydration from the α-face of the steroid and leads to the 4β-alcohol. The stereochemistry of 4β,17β-diacetoxy-19-nor-5β-androstane was established by X-ray crystallography.