To a solution of 0.331 g (0.921 mmol) of 1-(6,7-dihydro-4H-furo[3,2-c]pyridin-5-yl)-3-(3-phenethylphenyl) propan-1-one in 20 ml of acetic acid, 0.10 g (1.1 mmol) of 50% aqueous dimethylamine and 0.09 g (1.1 mmol) of 37% aqueous formaldehyde were added, followed by stirring at 100° C. for 15 minutes. After the solvent was distilled off under reduced pressure, the residual solution was alkalified with aqueous sodium hydroxide and extracted with dichloromethane 3 times. The combined organic layer was dried over anhydrous magnesium sulfate; the solvent was distilled off under reduced pressure. The resulting crude product was purified by silica gel column chromatography (ethyl acetate to ethyl acetate/methanol=4/1) to yield the desired product.
