Photochemical and Beckmann rearrangement of (Z)-cholest-4-en-6-one oxime

Beckmann rearrangement of (Z)-cholest-4-en-6-one oxime (4) (prepared in 4 steps starting from cholest-5-en-3?-ol ?1)) with thionyl chloride in dioxane solution afforded an enamide-type lactam, i.e. 7-aza-B-homocholest-4-en-6-one (6) as a single product. Photoreaction of the same compound in methanol or benzene-acetic acid solution gave a mixture of products, with the formation of the parent ketone 3 and the occurrence of Z/E isomerization, while the lactam 6 was obtained only when the reaction was performed in methanol and then in very low yield (7%).