[2 + 2] Photochemical Cycloaddition/Ring Opening of 6-Alkenyl-2,3-dihydro-4-pyridones

During the course of a study aimed at constructing azaspirocycles from 2,3-dihydro-4-pyridones, an unexpected product was obtained in the SET ring-opening reaction of photocycloadduct 1. Differences in reactivity between homologues 1 and 2 were observed in the presence of SmI₂. Tricyclic ketone 2 afforded azaspiro[5.5]undecane 15 when treated with SmI₂; however, when ketone 1 was submitted to similar reaction conditions a double ring-opening/reduction sequence gave cis-piperidinol 10.