Photo-induced molecular transformations. Part 87. Regiospecific photo-Beckmann rearrangement of steroidal α,β-unsaturated ketone oximes: synthesis of some steroidal enamino lactams

Abstract

While it is well known that the Beckmann rearrangement of steroidal cyclic α,β-unsaturated ketone oximes lead to the exclusive formation of enone-type lactams regardless of the initial geometry of their hydroxyimino group, the photolysis of three isomeric cholestenone oximes, (E)- and (Z)-cholest-4-en-3-one oximes, (E)-2,2-dimethylcholest-4-en-3-one oxime, and (E)-cholest-5-en-7-one oxime in protic solvents has shown that in each case an enamine-type lactam is the sole product (yield ⩽33%), no enone-type lactam being formed. This regiospecific photo-rearrangement may be of value for the preparation of these enamine-type lactams which cannot be achieved by the Beckmann rearrangement.