Reaction of 3,4-Diaroyl-1,2,5-oxadiazole-2-oxide with Hydrazine Hydrate

Previously, 2,5-diphenylpyridines, which is annelated at 3 and 4 positions with a heteroaromatic ring such as 1,2,5-oxa-, 1,2,5-thia-, and 1,2,5-selena-diazole, thiophene, IV-methylpyrrole,•1,2,3-triazole, pyrazole, imidazole, pyridine, and pyrazine, were prepared. These compounds are fluorescent in a solid state and are of interest as a light emitting material for an electroluminescence devicei). Earlier, it was reported that the reaction of 3,4-dibenzoyl-1,2,5-oxadiazole-2-oxide (la) with hydrazine dihydrochloride in refluxing methanol gave 1,2,5-oxadiazolo[3,4-d]pyridazine-1-oxide 2a2). In the reaction with an excess amount of hydrazine, it was expected that the deoxygenation of 1-oxide 2 might occur to afford 1,2,5-oxadiazolo[3,4-d] pyridazine 3, which is an azaanalogue of strongly fluorescent 4,7-diaryl-1,2,5-oxadiazolo[3,4-d] pyridinei'.