Scheme 1. General Procedure for the Synthesis of Compounds Containing the Pyrazolo[3,4-d]pyridazin-7-one Moiety.

(i) Conc. HCl/H₂O (1:1), NaNO₂/H₂O, 0 °C, 1 h; (ii) EtOH, NaOAc, 0 °C, 1 h; (iii) NaOEt, EtOH, rt, 1 h; (iv) hydrazine hydrate, EtOH, reflux, 1 h; (v) DMF, NaH, 0 °C, 30 min; (vi) SnCl₂·H₂O, EtOH, reflux, 1 h; (vii) MC, TEA, 0 °C, 1 h; (viii) CuI, K₂CO₃, DMSO, microwave, 150 °C; (ix) LiOH 1 M, rt, overnight; (x) DMF, HOBT, EDC·HCl, rt, −50 °C, overnight.