New Findings in Photochemistry of p-Nitrophenyl Azide in the Presence of an Amine: Generation and Trapping of Enamines

4,5-Dihydro-5-diethylamino-l-(p-nitrophenyl)-l, 2,3-triazole (3) was obtained in the photolysis of p-nitrophenyl azide (1) in triethylamine (TEA), for which the structure was determined by X-ray crystallographic analysis. The formation of the triazoline 3 is reasonably explained in terms of trapping of N,N-diethylvinylamine (5) generated in situ with the starting azide 1. The reaction sequence involving a single electron transfer from TEA to the electronically excited azide is proposed for the formation of the enamine 5.