To 5 mL of a chloroform solution containing 301 mg of 1-(2-(4-aminopiperidin-1-yl)ethyl)-7-fluoroquinoxalin-2(1H)-one and 143 mg of 4-ethylbenzaldehyde, 60 μL of acetic acid were added, and stirred at room temperature for 1 hour. To the reaction mixture, 352 mg of sodium triacetoxyborohydride was added, and stirred for 1.5 hours. Aqueous saturated sodium hydrogen carbonate solution was added, the organic layer was separated. The organic layer was washed with aqueous saturated sodium chloride solution, dried over anhydrous magnesium sulfate, and the solvent was removed under reduced pressure. The residue thus obtained was purified by silica gel column chromatography [Silica Gel; Fuji Silysia Chemical Ltd., Chromatorex-NH, eluent; ethyl acetate:hexane=1:1], to give 1-(2-(4-(4-ethylbenzylamino)piperidin-1-yl)ethyl)-7-fluoroquinoxalin-2(1H)-one as pale yellow solid.
