Photoinduzierte 1, 3‐dipolare Cycloaddition von 3‐Phenyl‐2 H ‐azirinen an Azodicarbonsäure‐diäthylester. 32. Mitteilung über Photoreaktionen

Irradiation of 2, 2‐dimethyl‐3‐phenyl‐ ( 1a ), 2, 3‐diphenyl‐2 H ‐azirine ( 1b ) or the azirine‐precursors 1‐azido‐1‐phenyl‐propene ( 2a ) and 1‐azido‐1‐phenyl‐ethylene ( 2b ), respectively, in benzene in the presence of azodicarboxylic acid diethylester, yields the corresponding 1, 2‐carbethoxy‐3‐phenyl‐Δ 3 ‐1, 2, 4‐triazolines 4a–d ( Scheme 1 ). Refluxing 4 ( a, c or d ) in 0, 2–0, 4 M aqueous ethanolic potassium hydroxide leads to the formation of the 1‐carbethoxy‐3‐phenyl‐Δ 2 ‐1, 2, 4‐triazolines 6 ( a, c or d ). Under the same conditions 4b is converted to 3, 5‐diphenyl‐1, 2, 4‐triazole ( 7b , Scheme 2 ). In 10 M aqueous potassium hydroxide solution heating of either 4 ( c or d ) or 6 ( c or d ) yields the 3‐phenyl‐1, 2, 4‐triazoles 7 ( c or d ). Photolysis of 1‐carbethoxy‐5, 5‐dimethyl‐3‐phenyl‐Δ 2 ‐1, 2, 4‐triazoline ( 6a ) in benzene in the presence of oxygen and trifluoroacetic acid methylester gives the 5‐methoxy‐2, 2‐dimethyl‐4‐phenyl‐5‐trifluoromethyl‐3‐oxazoline ( 13 , Scheme 5 ). 5, 5‐Dimethyl‐3‐phenyl‐1, 2, 4‐triazole seems to be the intermediate, which on losing nitrogen gives the benzonitrile‐isopropylide ( 3a ).