A DMI (20 ml) suspension of tert-butyl 4-{3-[(methylsulfonyl)oxy]propyl}piperidine-1-carboxylate (1.00 g), 1-piperazin-1-yl-isoquinoline dihydrochloride (980 mg), cesium carbonate (1.02 g) and sodium iodide (467 mg) was stirred at 140° C. for 1 hour. EtOAc was added to the reaction liquid, washed with water and aqueous saturated sodium hydrogencarbonate solution in that order, then dried over anhydrous magnesium sulfate, and the solvent was evaporated. The residue was purified by silica gel column chromatography (eluent: hexane:EtOAc=1:1 (v/v)) to obtain tert-butyl 4-[3-(4-isoquinolin-1-ylpiperazin-1-yl)propyl]piperidine-1-carboxylate (1.07 g) as a pale yellow oil.
