Acid-catalyzed and photolytic reactivity of some unsaturated B-nor-5,10-secosteroidal ketones

The acid-catalyzed reaction of (Z)- and (E)-B-nor-5,10-seco-ketones 2 and 3 resulted in an intramolecular cyclization to give the 5-hydroxy-A-nor-1b,5b-10(19)-methylidene derivative 8, the 5b-hydroxy-A-nor-1(10)-unsaturated compound 9 and the 5b,10a-dihydroxy-A-nor-product 10, from the (Z)-isomer and the 5-hydroxy-A-nor-1a,5b-10(19)-methylidene product 11, from the (E)-isomer. Upon UV-irradiation, the (Z)- and (E)-seco-ketones 2 and 3 underwent a reversible (Z)/(E) and (E)/(Z)-isomerization and in addition to a transannular photocyclization to afford the 10(19)-methylidene derivatives 8 and 11, respectively, while photolysis of the 10(19)-methylidene-B-nor-5,10-seco-ketone 4 gave the oxetane derivative 12.