To a solution of 0.230 g (0.748 mmol) of 1-(5,7-dihydro-4H-furo[2,3-c]pyridin-6-yl)-2-(2-naphthoxy)ethan-1-one in 20 ml of acetic acid, 0.10 ml (1.1 mmol) of 50% aqueous dimethylamine and 0.092 ml (1.1 mmol) of 37% aqueous formaldehyde were added, followed by stirring at 100° C. for 45 minutes. After the solvent was distilled off under reduced pressure, the residual solution was alkalified with aqueous sodium hydroxide and extracted with dichloromethane 2 times. The combined organic layer was washed with water and dried over anhydrous sodium sulfate; the solvent was distilled off under reduced pressure. The resulting crude product was purified by silica gel column chromatography (ethyl acetate/methanol=9/1 to 6/1) to yield the desired product.
