To a solution of 0.393 g (1.093 mmol) of 1-(5,7-dihydro-4H-furo[2,3-c]pyridin-6-yl)-3-(3-phenethylphenyl) propan-1-one in 20 ml of acetic acid, 0.14 ml (1.3 mmol) of diethylamine and 0.11 g (1.3 mmol) of 37% aqueous formaldehyde were added, followed by stirring at 100° C. for 1 hour. 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=9/1) to yield the desired product.
