To 3 mL of dichloromethane solution containing 70 mg of (2-oxoquinoxalin-1(2H)-yl)acetaldehyde, 98 mg of N-(piperidin-4-yl)-2,3-dihydro-1,4-benzodioxin-6-carboxamide and 21 μl of acetic acid were added and stirred at room temperature for 2 hours. To the reaction mixture, 0.12 g of sodium triacetoxyborohydride was added and stirred at the same temperature for 30 min. Chloroform and aqueous saturated sodium hydrogen carbonate solution were added, the organic layer was separated, and the aqueous layer was extracted with chloroform. The organic layer and extracts were combined, 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 [eluent; chloroform:methanol=20:1], and to the residue thus obtained, diethyl ether was added, and the resulting solid was filtered to give 0.12 g of N-(1-(2-(2-oxoquinoxalin-1(2H)-yl)ethyl)piperidin-4-yl)-2,3-dihydro-1,4-benzodioxin-6-carboxamide as a light brown solid.
