AbstractIrradiation at 2537 Å eliminates carbon dioxide from 3‐phenyl‐ Δ2‐oxadiazol‐5‐one in either methanol or dioxane. A migration of phenyl from carbon to nitrogen leads to phenylcarbodiimide (8) which tautomerizes into phenylcyanamide (10). Benzamidine (11) and the0‐methyl ether (12) of benzamidoxime apparently result from hydrogen abstraction and insertion reactions of an intermediate unrearranged azomethine nitrene (9). More extensive fragmentation produces benzonitrile (7), which is isolated, and presumably phenylcarbene (20) to account for benzyl methyl ether (15). Generation of the carbene is discussed. The formation of 3,5‐diphenyltriazole (6), triphenyltriazine (16) andN‐cyanobenzamidine (15) re