Photo-induced transformations. Part 44. Formation of lactams in the photolysis of some steroidal acetylhydrazones in the presence of oxygen

Abstract

Irradiation of 3α-acetoxy-5α-androstan-17-one acetylhydrazone (3) or 3β-acetoxyandrost-5-en-17-one acetylhydrazone (5) in dioxan in the presence of oxygen afforded 17-oxo-17a-aza-D-homosteroid [(6) or (11)] and its 13α-isomer [(7) or (12)], while when oxygen was excluded none of these lactams were formed under otherwise similar conditions. 5α-Cholestan-6-one acetylhydrazone (20) under similar conditions also afforded very low yields of 6-aza-D-homo-5α-cholestan-7-one (21) and 7-aza-B-homo-5α-cholestan-6-one (22) upon photolysis. In contrast with the acetylhydrazones, the corresponding hydrazone (2), upon photolysis in dioxan without the exclusion of oxygen, afforded the corresponding azine (13) without any accompanying lactams [(6) and (7)]. There is a distinct difference in behaviour between the hydrazones and the N-acetyl derivatives towards oxygen under irradiation. Although as yet no definite conclusion can be drawn on the mechanism of lactam formation, some plausible paths are discussed.