Phototransformation of 1,2,4-Triazolopyridazine-1,3-dione to Pyrrolo-1,3,5-triazine-2,4-dione

Article abstract of DOI:10.1021/jo00178a002

5-(Methoxycarbonyl)-2-phenyl-1,2,4-triazolo<1,2-a>pyridazine-1,3-dione (3) was obtained by a Diels-Alder reaction of 3-(methoxycarbonyl)-2-pyrone (1) with 4-phenyl-1,2,4-triazoline-2,5-dione (2).The photolysis of 3 in methanol yielded the 6-methoxy-9-methoxycarbonyl and 6-methoxycarbonyl derivatives of 3-phenylpyrrolo<1,2-a>-1,3,5-triazine-2,4-dione (7 and 8, respectively) while photolysis in dichloromethane yielded the 8-methoxycarbonyl derivative 10.All the photoproducts were formed via a triazonine (5) which underwent either transannular addition of methanol to give 7, addition-elimination of methanol to 8, or further photolysis to 10.