A new route for the synthesis of substituted pyridazines

Condensation of 4-acetyl-5,6-diphenyl-2,3-dihydropyridzin-3-one (1) with dimethylformamide dimethylacctal (DMFDMA) afforded the enaminone 2. This could be converted into the pyrazolylpyridazine derivative 4 on reaction with hydrazine hydrate and into pyridazinylpyridazinone 7a,b via coupling with aromatic diazonium salts and subsequent treatment with active methylene compounds. The reaction of 6 with dimethyl acetylenedicarboxylate in the presence of triphenylphosphine afforded the pyridazinylpyridazine derivative 8. Compound 1 converted into 9 upon reflux in acetic acid in the presence of ammonium acetate and afforded 10 on reflux in acetic acid.