Sodium hydride (60% dispersion in oil, 1.59 g) was added to a DMF solution (100 ml) of ethyl 3-(2-nitrobenzyl)-2-oxo-3-piperidinecarboxylate (11.0 g) and propyl iodide (5.79 ml) under ice-cooling. The reaction mixture was stirred at room temperature for 30 minutes. The reaction mixture was diluted with water and extracted with a mixture of ethyl acetate and diethyl ether. The residue was purified by silica gel column chromatography (eluent: ethyl acetate/hexane=1/4 to 1/2) to obtain the entitled compound (10.6 g).
