To a solution of 0.503 g (1.548 mmol) of 1-(5,7-dihydro-4H-thieno[2,3-c]pyridin-6-yl)-6-phenylhexan-1-one in 20 ml of acetic acid, 0.17 g (1.9 mmol) of 50% aqueous dimethylamine and 0.15 g (1.9 mmol) of 37% aqueous formaldehyde were added, followed by stirring at 100° C. for 3 hours. Additionally, 0.5 g (5.5 mmol) of 50% aqueous dimethylamine and 0.5 g (6.2 mmol) of 37% aqueous formaldehyde were added, followed by stirring at 100° C. for 6 hours. 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.
