[2+2] Photocycloadditions and Photorearrangements of 2-Alkenylcarboxamido-2-cycloalken-1-ones

While intermolecular photocycloaddition of alkenes with 2-carboxamidocyclo-2-pent-1-enones was not an efficient process, photolysis of 2-alkenylcarboxamido-2-cycloalken-1-ones led regio- and stereospecifically to a faster [2+2] intramolecular reaction and therefore to the corresponding cyclobutanes. However, photorearrangements involving three different intramolecular H-abstraction processes, compete with the observed cycloaddition. To explain the results, we propose that different deactivation pathways are available to the excited state, depending on the conformers present in the starting material.