Synthesis, structure, and reactivity of secosteroids containing a medium-sized ring. Part 32. Conformations and photochemical reactivity of some unsaturated 5,10-secosteroidal ketones
UV irradiation of the unsaturated (E)-5,10-secosteroidal ketones 1 and 6 results, in addition to (E/Z)-isomeri-zation, in an intramolecular Pateino-Büchi reaction and, in the case of 1, in transannular cyclization (along with AcOH elimination). The stereochemistry of the observed intramolecular photoprocesses can be explained in terms of ground-state conformations of the (E)-seco-ketones 1 and 6 in