To a slightly heterogeneous solution of piperidine (99.7 mg, 1.17 mmol) and toluene (8 mL) cooled to −78° C. was slowly added dropwise an n-BuLi solution (0.235 mL, 0.59 mmol, 2.5 M in hexanes). After stirring at −78° C. for 10 minutes, the cooling bath was removed and the mixture stirred an additional 1 hour at 23° C. The 2-(4-fluorophenyl)-4-methoxy-5-[4-(methylthio)phenyl]-3(2H)-pyridazinone (400 mg, 1.17 mmol) was dissolved in portions in toluene (3×6-7 mL aliquots) with a heat gun and cooled to 0° C. prior to transfer via syringe to the lithium amide solution (cooled to −78° C.). The addition was made slowly along the interior wall of the reaction vessel. This reaction mixture was stirred overnight, slowly warming to 23° C. as the cooling bath evaporated. The reaction was quenched with water and diluted with a large excess of ethyl acetate. The layers were separated, and the ethyl acetate layer washed with additional water and brine and dried over MgSO4, filtered, and concentrated in vacuo. The residue was chromatographed (flash silica gel, ethyl acetate/hexanes 1:2) to provide 440 mg (95%) of 2-(4-fluorophenyl)-5-[4-(methylthio)phenyl]4-piperidino-3(2H)-pyridazinone.
