Synthesis, structure, and reactivity of secosteroids containing a medium‐sized ring. Part 32. Conformations and photochemical reactivity of some unsaturated 5,10‐secosteroidal ketones

Abstract

UV irradiation of the unsaturated (E)‐5,10‐secosteroidal ketones 1 and 6 results, in addition to (E/Z)‐isomerization, 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 solution.