To 5 mL of dichloromethane solution containing 0.15 g of (2-oxoquinolin-1(2H)-yl)acetaldehyde, 0.27 g of tert-butyl(2,3-dihydro-1,4-benzodioxin-6-ylmethyl)(piperidin-4-yl)carbamate, 45 μL of acetic acid and 0.25 g of sodium triacetoxyborohydride were added and stirred for 4 hours. To the reaction mixture, water and ethyl acetate were added, neutralized with aqueous saturated sodium hydrogen carbonate solution, thereafter the organic layer was separated, and the aqueous layer was extracted with ethyl acetate. 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=100:1], to give 0.13 g of tert-butyl(2,3-dihydro-1,4-benzodioxin-6-ylmethyl)(1-(2-(2-oxoquinolin-1(2H)-yl)ethyl)piperidin-4-yl)carbamate as a yellow oil.
