Efficient photoreduction and ring contraction of 3,5,6-triphenyl-1,2,4-triazine in neat triethylamine

Broad band u.v. irradiation of 3,5,6-triphenyl-1,2,4-triazine (1) in neat t riethylamine as solvent leads to rapid degradation of the starting material and N-dealkylation of the amine accompanied by build-up of the reduction p roduct 2,5-dihydro-3,5,6-triphenyl-1,2,4-triazine (5) as well as the produc ts of reductive ring contraction: 3,5-diphenyl-1,2,4-triazole (8) and 2,3-d i-(3,5-diphenyl-1,2,4-triazol-1-yl)butane (13), the latter as a mixture of rac- and meso- diastereomers. In addition, a hitherto unidentified labile p hoto reduction product gives rise to formation of benzil during chromatogra phic work-up. A rationale to explain all observations is presented.