Novel synthesis of pyridopyridazine, pyrrolopyridazine and some pyridazine derivatives

Ethyl-1-aryl-5-cyano-1,6-dihydro-4-methyl-6-oxopyridazin-3-carboxylates (1) react with hydrazine hydrate in ethanol to give the corresponding hydrazide (2). Compounds 2 gave the carboazides 3 upon treatment with nitrous acid. The carboazides (3) react with different alcohols, different amines and hydrazine hydrate to give the corresponding carbamate, substituted urea, and semicarbazide derivatives 5-7, respectively. Also compound 3 when refluxed in xylene gave pyrrolopyridazine (4). Compound 1 reacts with aromatic aldehydes to give styryl derivative 8 which upon refluxing with hydrazine hydrate gave the corresponding hydrazide (9) which undergoes cyclization to pyridopyridazine (10) upon treatment with Cu2Cl2.