Photochemical Studies. 16.¹ Irradiation Induced Transformations of 1, 2-Dihydrophthalimides and Related Compounds

Norbornen-7-one-5, 6-dicarboximides (6a-c) decarbonylate thermally and photochemically to the corresponding 1, 2-dihydrophthalimides (5). The latter undergo the following wavelength and substitution dependent photochemical transformations via singlet excited states; fragmentation to benzene and benzamides (7), electrocyclic closure to onfi-bicyclo[2.2.0]hex-2-ene-5, 6-dicarboximides (8), a 1, 2-acyl shift to bicyclo[3.1.0]hex-3-ene-2, 6-dicarboximides (10), and a degenerate 1, 5 shift which leaves 5 structurally unchanged. The triplet excited states, reached both by direct irradiation or sensitization, lead only to photodimers. A mechanism involving α cleavage via diradical intermediates is invoked for those photochemical processes in which the imide moiety takes active part.