Irradiation of 2,2-dimethyl-3-phenyl- (1a), 2,3-diphenyl-2H-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 diethylestcr, yields the corresponding 1,2-carbethoxy-3-phenyl-delta3-1,2,4-triazolines 4a-d (Scheme 1).
Refluxing 4 (a, c or d) in 0.2-0.4M aqueous ethanolic potassium hydroxide leads to the formation of the 1-carbethoxy-3-phenyl-delta2-1,2,4-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 10M 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-delta2-1,2,4-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).