To 1 mL of a chloroform solution containing 0.20 g of tert-butyl (2,3-dihydro-1,4-benzodioxin-6-ylmethyl)(piperidin-4-yl)carbamate, 0.14 g of (5-nitro-2-oxoquinolin-1(2H)-yl)acetaldehyde, 10 μL of acetic acid and 0.18 g of sodium triacetoxyborohydride were added and stirred at room temperature for 2 nights. Aqueous saturated sodium hydrogen carbonate solution was 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[Silica Gel; Kanto Chemical Co., Inc., Silica Gel 60, eluent; ethyl acetate], to give 0.24 g of tert-butyl (2,3-dihydro-1,4-benzodioxin-6-ylmethyl)(1-(2-(5-nitro-2-oxoquinolin-1(2H)-yl)ethyl)piperidin-4-yl)carbamate as a yellow foam.
