To a solution of the compound obtained in Example 1 (157 mg, 0.53 mmol) in DMF (15 ml), potassium carbonate (80 mg, 0.58 mmol), 2,6-difluorobenzyl chloride (103 mg, 0.64 mmol) and potassium iodide (44 mg, 0.26 mmol) are added, followed by stirring at about 15 to 25° C. for 1 hour and stirring under heating at 80° C. for 1 hour. The brownish white crystalline substance obtained by concentration under reduced pressure of the reaction mixture is dispensed to ethyl acetate (30 ml) and water (30 ml). The water layer is extracted with ethyl acetate (10 ml), and the organic layers are combined and dried over sodium sulfate, after which the solvent is distilled off under reduced pressure to yield a crude brownish white crystalline product (204 mg), which is then purified by flush column chromatography to yield a white crystal (146 mg, 65%).
