To a solution of 2-benzyl-5-chloro-4-methoxypyridazin-3(2H)-one (20 g, 80 mmol) and 4-chlorophenylboronic acid (15.6 g, 100 mmol) in toluene/EtOH (2:1, 600 mL) at RT under argon was added (Ph3P)4Pd (1.85 g, 1.8 mmol) and 2 M aqueous Na2CO3 solution (160 mL, 320 mmol). The resulting suspension was heated at 90° C. for 16 h with stirring. HPLC/MS indicated about 4% of the 2-benzyl-5-chloro-4-methoxypyridazin-3(2H)-one still remained. After cooling the reaction mixture to RT, the solution was extracted with CH2Cl2 (2×150 mL). The combined organic layers were dried (Na2SO4), filtered and concentrated under vacuum. The crude product was purified by silica gel column chromatography (ISCO) eluting with hexanes/EtOAc to obtain pure title compound, 2-Benzyl-5-(4-chlorophenyl)-4-methoxypyridazin-3(2H)-one, (21.7 g, 83%) as a white solid. MS [M+H]+ 327; HPLC retention time=3.85 min.
