Phototransformations of C-benzoylaziridines. Dipolarophilic trapping of photogenerated azomethine ylides

The phototransformations of a few 2,3-diaroylaziridines and 2-aryl-3-aroylaziridines have been studied by steady-state photolysis and product analysis. The formation of various photoproducts could be substantiated by ring opening via C-C bond cleavage (leading to azomethine ylides), intramolecular hydrogen abstraction, and C-N bond cleavage. Isolation of stereospecific 3-pyrroline derivatives from the photoreaction of benzoylaziridines in the presence of DMAD confirms our previous results concerning the azomethine ylides as major transient intermediates, produced under laser pulse photoexcitation. Dimethyl 1-cyclohexyl-2-benzoylpyrrole-3,4-dicarboxylate (25), one of the photoadducts derived from the reaction of 1a and 1b with DMAD undergoes a novel and unusual photorearrangement to give dimethyl 2-(1-benzoylcyclohexyl)pyrrole-3,4-dicarboxylate (27), the structure of which was confirmed through X-ray crystallographic analysis.