1.0 g (3.47 mmol, 1.0 equivalent) of 4-[(4-dipropylaminobutyl)amino]methylbenzonitrile (2a), 10 ml of ethanol, and 684 mg (5.21 mmol, 1.5 equivalents) of 4-cyanobenzaldehyde were charged in a 100 ml three-necked flask. The mixture was cooled to −30° C. After the addition of 1.47 g (6.95 mmol, 2.0 equivalents) of sodium triacetoxyborohydride, the mixture was stirred for six hours and further stirred at room temperature for 12 hours. After confirming the disappearance of the raw material, the reaction solution was added into 50 ml of a saturated sodium bicarbonate aqueous solution, and extracted with 100 ml of chloroform. The chloroform layer was washed with 50 ml of a saturated sodium chloride aqueous solution, dried over anhydrous sodium sulfate, and concentrated, thereby obtaining 1.35 g of 4-[(4-dipropylaminobutyl)-4-cyanobenzylamino]methylbenzonitrile (12) as a colorless oily substance (yield: 97%, GC: 87%).
