Sodium hydride (60% in mineral oil, 32 mg, 1.75 mmol) was added to a solution of 4-chloro-3-iodo-5-phenyl-1H-pyrazolo[3,4-c]pyridazine (400 mg, 1.12 mmol) and 2-chloro-1-(pyrrolidin-1-yl)ethanone (54 mg, 1.8 mmol) in dry DMF (7.5 mL) at room temperature. After 1.5 h at room temperature further sodium hydride (60% in mineral oil, 27 mg) was added and the suspension stirred for 2 h. 4% LiCl aq. solution and ethyl acetate was added. The layers were separated and the aqueous was extracted with ethyl acetate. The combined organics were dried (MgSO4), filtered and concentrated in vacuo. The residue was partially purified by column chromatography (silica gel, isohexane/ethyl acetate 1:0 to 0:1). The resulting solid was dissolved in minimum CH2Cl2 and diethyl ether was added until a solid precipitated. The solid was collected by filtration to provide 2-(4-chloro-3-iodo-5-phenyl-1H-pyrazolo[3,4-c]pyridazin-1-yl)-1-(pyrrolidin-1-yl)ethanone (246 mg).
