Reduction of 1-oxo-steroids by sodium borohydride

Abstract

Reduction with sodium borohydride of steroidal 1-ones in the 5α-series affords the corresponding axial 1α-hydroxy-derivatives, whereas the isomeric ketones in the 5β-series give the equatorial 1α-hydroxy-derivatives. Conversely, reduction of 4β,5β- and of 5β,6β-epoxy-1-oxo-steroids takes place by rear-side attack to give the corresponding 1β-hydroxy-derivatives. All these reactions are stereospecific. The reduction of various 2-en-1-ones in the 5α-series proceeds by 1,2-attaek to give mixtures of 1α- and 1β-allylic alcohols, in contrast to the reduction of the isomeric enones in the 5β-series which proceeds by 1,4-attack to give the corresponding saturated ketones, in most instances further reduced to the saturated α-oriented alcohols. Similar saturation of the double bond was observed for 5β-2-en-4-one derivatives.