Irradiation of 5-phenyl-1, 2, 4-thiadiazole (6) resulted in the formation of benzonitrile (5), 3- phenyl-1, 2, 4-thiadiazole (4), phenyl-and diphenyl-1, 3, 5-triazines (7 and 8), and a trace quantity of diphenyl-1, 2, 4-thiadiazole (9). The formation of 4, 5, 7, and 8 can be explained in terms of photoinduced electrocyclic ring closure resulting in the formation of an intermediate 4-phenyl-1, 3-diaza-5-thiabicyclo [2.1. 0] pentene. 15N-labeling experiments ...
