To 5 mL of dichloromethane solution containing 0.18 g of tert-butyl(2,3-dihydro-1,4-benzodioxin-6-ylmethyl)(piperidin-4-yl)carbamate, 0.15 g of (5-bromo-7-methoxy-2-oxoquinolin-1(2H)-yl)acetaldehyde and 29 μl of acetic acid were added and stirred at room temperature for 1 hour. To the reaction mixture, 0.16 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 sequentially with water and 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; ethyl acetate] to give 0.17 g of tert-butyl(1-(2-(5-bromo-7-methoxy-2-oxoquinolin-1(2H)-yl)ethyl)piperidin-4-yl)(2,3-dihydro-1,4-benzodioxin-6-ylmethyl)carbamate as a light brown foam.
