Synthesis and antimicrobial activity of pyrazolo[3 ',4 ': 4,3]pyrido[6,5-c]pyridazine and thieno[2,3-c]pyridazine derivatives

4-Acetyl-5,6-diphenyl-2(H)pyridazin-3-one (1) was allowed to react with phe nyl hydrazine to afford the corresponding hydrazone 2. Hydrazone 2 upon tre atment with Vilsmeier's reagent gave pyrazolylpyridazine derivative 3, whic h was allowed to react with thiosemicarbazide and hydroxyl amine to give th e corresponding thiosemicarbazone and oxime 4 and 5, respectively. Treatmen t of oxime 5 with Ac2O gave the pyrazolylpyridazine carbonitrile derivative 6. Compound 5 reacts with POCl3 to give the corresponding chloro compound 7. The chloro compound 7 was reacted with hydrazine hydrate or aniline to a fford pyrazolopyridazodiazepine 9 or pyrazolopyridazopyridazine 10. When co mpound 1 was allowed to react with POCl3 the chloro derivative 11 resulted. This compound reacts with thiourea, piperidine or hydrazine hydrate to giv e compounds 12, 14 and 15, respectively. Compound 12 reacted with alpha-hal oester or alpha-haloketone to give the thienopyridazines 13a and b, respect ively. Most of the newly synthesized compounds were screened for fungicidal and bactericidal activity.