Under a nitrogen atmosphere, anti-isomers of 2-benzylidenehydrazinopyrimidines underwent isomerization easily to their syn-isomers by irradiation with ultraviolet light in a benzene solution, but in the presence of oxygen, photosensitized auto-oxidation occurred to afford 3-aryl-1, 2, 4-triazolo [4, 3-a] pyrimidines. When irradiated in the same manner, 2-benzylidenehydrazino-1, 3, 5-triazine derivatives decomposed into benzaldehydes and 2-hydroxy-1, 3, 5-triazines.
