Novel azaandrostane derivatives for the synthesis of 17β‐( N ‐ tert ‐butyl carbamoyl)‐4‐aza‐5α‐androst‐1‐ene‐3‐one

A new industrially viable process for the preparation of 1β‐( N ‐ tert ‐butyl carbamoyl)‐4‐aza‐5α‐androst‐1‐ene‐3‐one, also known by the generic name finasteride ( 6 ) from the new azaandrostane derivatives such as 1β‐( N ‐ tert ‐butyl carbamoyl)‐4‐benzoyl‐4‐aza‐5α‐androstane‐3‐one ( 4 ), 1β‐( N ‐ tert ‐butyl carbamoyl)‐4‐benzoyl‐4‐aza‐5α‐androst‐1‐ene‐3‐one ( 5 ) is reported. In this process, benzoyl group is demonstrated as a novel protecting group for lactamic NH group. The structures of newly prepared compounds were established on the basis of spectral data (IR, 1 H‐NMR, and MS).