2-(Trichloromethyl)-1H-benzimidazole (19 g) and 1-tert-butyl 3-methyl (3R,5S)-5-[(2-methylpropyl)amino]piperidine-1,3-dicarboxylate (25 g) were dissolved in THF (1200 ml), sodium hydrogen carbonate (67 g) and water (600 ml) were added, and the mixture was stirred at room temperature for 1 hr and at 50° C. for 1 hr. After evaporation of the solvent, the residue was extracted 3 times with ethyl acetate (700 ml). The extract was washed successively with 10%-aqueous citric acid solution (500 ml) and brine, and dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure. The residue was dissolved in ethyl acetate (1000 ml), subjected to basic silica gel column chromatography, and a fraction eluted with ethyl acetate was concentrated under reduced pressure to give the object product (30.6 g).
