(R)-2-Methylpiperazine-1-carboxylic acid benzyl ester (4.42 g, 18.9 mmol), 1-benzyloxy-4-bromobenzene (5.95 g, 22.6 mmol), cesium carbonate (8.60 g, 26.4 mmol) and toluene (49 ml) were mixed, and the atmosphere was replaced with nitrogen. Palladium acetate (0.42 g, 1.9 mmol) and tri-tert-butylphosphine tetrafluoroborate (0.66 g, 2.3 mmol) were added thereto and stirred at 90 to 100° C. for 2 days. Water and ethyl acetate were added to the reaction mixture, the mixture was filtered through Celite to remove insoluble matter. The filtrate was separated into layers. The organic layer was washed with a saturated sodium chloride aqueous solution, dried over magnesium sulfate and concentrated. The residue was purified by silica gel column chromatography (hexane:ethyl acetate=100:0→70:30) to afford the title compound as a brown oil (6.18 g, 79%).
