[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-alkenylcarbox amido-2-cycloalken-1-ones led regio- and stereospecifically to a faster [22] intramolecular reaction and therefore to the corresponding cyclobutanes. However, photorearrangements involving three different intramolecular H-ab straction processes, compete with the observed cycloaddition. To explain th e results, we propose that different deactivation pathways are available to the excited state, depending on the conformers present in the starting mat erial. (C) 2000 Elsevier Science Ltd. All rights reserved.