To a solution of the compound (20.4 g) obtained in step 1 and N-(methoxymethyl)-N-(trimethylsilylmethyl)benzylamine (22.0 g) in toluene (180 mL) was added a solution of trifluoroacetic acid (1.31 mL) in toluene (18 mL) at 0° C., and the mixture was stirred at room temperature for 14 hr. To the reaction solution was added ethyl acetate (300 mL), and the mixture was washed with saturated aqueous sodium hydrogen carbonate solution, water and saturated brine and dried, and the solvent was evaporated under reduced pressure. The obtained residue was purified by silica gel column chromatography (solvent gradient; 10→25% ethyl acetate/hexane) to give methyl (3R*,4S*)-1-benzyl-4-(3,4-dichlorophenyl)pyrrolidine-3-carboxylate (33.4 g, 100%) as a pale-yellow oil.
