Studies using (E)-6-oxo-1-aryl-4-(2-N-piperidinyl)vinyl-1,6-dihydropyridazine-5-carbonitrile

Condensing 1-aryl-4-methyl-1,6-dihydropyridazine-5carbonitrile with triethyl orthoformate and piperidine afforded the trans-enamine 2. This could be converted into pyrido[3,4-d]pyridazine 3 upon treatment with primary aromatic amines. Reacting 2 with hydrazonoyl chlorides 5 afforded 7 rather than 6. Compound 2 gives also pyrido[3,4-d]pyridazine 10 upon treatment with acetic acid and ammonium acetate. Compound 2 afforded N-aminopyrido[3,4-dlpyridazine 11 upon treatment with hydrazine hydrate. Compound 11 reacted with triethyl orthoformate to give [1,2,4]triazolo[2',3':1,2]pyrido[4,3-d]pyridazin-10-one 12 and can be acetylated to 13. Compound 2 could be coupled with p-chlorobenzenediazonium chloride to give the pyridazino[4,5-d]pyridazine 17.