Synthesis and reactivity of some pyridazine derivatives

Ethyl 3-hydroxy-5,6-diphenyl pyridazine-4-carboxylate ((1) under bar) undergoes hydrazinolysis by hydrazine hydrate to give corresponding carbohydrazide (2) under bar. The reacton of (2) under bar with HNO2, CS2/NaOH, and PhNCS followed by treatment with NaOH gives compounds (3) under bar,(7) under bar, and <(10)under bar> respectively. Acyl azide (3) under bar undergoes Curtius rearrangement when heated with alcohols, amines, or when heated in an inert solvent to give compounds (4) under bar-(6) under bar, When compound (1) under bar is heated with POCl3, ethyl (3) under bar-chloro-5,6-diphenyl-4-carboxylate <(11)under bar> is formed. This compound is converted into the corresponding mercapto derivative <(12)under bar>, upon treatement with thiourea, NaOH and posteuer acidification with HCl. Compound <(12)under bar> was alkylated to give the s-alkylated derivative <(14)under bar>. Both compounds <(11)under bar> and <(12)under bar>, when treated with hydrazine hydrate gave the pyrazolopyridazine derivative <(13)under bar>.