1,3-dipolar cycloadditions of anhydro 1-phenylimino-2,4,5-triphenyl-1,2,3-triazolium hydroxide

Anhydro 1-phenylimino-2,4,5-triphenyl-1,2,3-triazolium hydroxide (3), the oxidation product of benzil bisphenylhydrazone (1) gave 1:1-cycloadducts with a wide variety of acetylenic and olefinic dipolarophiles, yielding pyrazolino[2,3-c] and dihydropyrazolino[2,3-c] [1,2,3]-triazoles. With phenyl isocyanate and phenyl isothiocyanate 3 gave 1,3,3a,4,6-pentaphenyl-1,2,4-triazolidono[1,5-c] [1,2,3] triazol-5-one and the corresponding thione, respectively. The initially formed cycloadduct in the case of carbon disulphide fragmented to give 2,4,5-triphenyl-1,2,3-triazole. The same triazole was obtained in the thermal decomposition of the cycloadducts obtained from the reaction of 3 with dimethyl maleate and dimethyl fumarate. Kinetic studies indicate that these addition reactions are examples of concerted 1,3-dipolar cycloadditions