No abstract

The pyrolysis of 1‐aroylamino‐4,5‐diphenyl‐1,2,3‐triazoles 1 yields, pressumably via the 4,5‐diphenyl‐1,2,3‐triazolyl radical (2a), 2,3‐diphenyl‐2H‐azirine (11a) and 2‐aryl‐4,5‐diphenylimidazoles 14 as the major products. Upon irradiation 1‐benzoylamino‐4,5‐diphenyl‐1,2,3‐triazole (1a) gives 4,5‐diphenyl‐1 (2)H‐1,2,3‐triazole (4a) via the 1,2,3‐triazolyl radical 2a, together with benzamide (5a) and 1,2‐bisbenzoylhydrazine (6a). Products 5a and 6a result from the benzoylamino radical 3a by hydrogen atom abstraction and dimerization respectively.

The synthesis and lead tetraacetate oxidation of the title mono‐ and bis‐arylhydrazones to the corresponding 5‐acyl‐4‐aryl(alkyl)‐2‐aryl‐1,2,3‐triazole 1‐oxides is described.

The title compounds 3a-h were synthesized by condensation of ( E )-benzil monoxime 2 with the appropriate substituted aniline, 1 followed by oxidative cyclization to the corresponding 2,3-diphenylquinoxaline 1-oxides 4a-h using lead tetraacetate.Quinoxaline 1-oxides are usually prepared from the parent heterocycle by use of oxidants such as peracetic acid, 3 -chloroperoxybenzoic acid, permaleic acid, etc. 8 Excluding the unusual, albeit existent, danger of an explosion, 1 the main disadvantages of the procedure involving the oxidation of the parent heterocycle are the lack of regioselectivity in those cases where nonsymmetric substrates are used, and the frequent isolation of mixtures of mono-and di-N -oxides. 2, 8 Contrary to this in our procedure the milder oxidant lead tetraacetate was used in the place of peracids and the mono-N -oxides 4 were the only products of the reaction. Moreover, with the exception of the oxidative cyclization of m-substituted α -arylimino oxime 3a where a small amount (6%) of a second isomer 4e' was isolated (Table), in all cases the outcome of the reaction was a single product in fair to good yields.

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