Benzyl(methoxymethyl)((trimethylsilyl)methyl)amine → Benzyl (3RS,4SR)-1-benzyl-4-methylpyrrolidine-3-carboxylate

Benzyl (2E)-but-2-enoate obtained in Example 1e (20.5 g, 116 mmol) was dissolved in dichloromethane (5 ml), and the mixture was cooled in an ice bath with stirring. Trifluoroacetic acid (257 μl, 3.47 mmol) was added, and N-(methoxymethyl)-N-(trimethylsilylmethyl)benzylamine (33.1 g, 139 mmol) was added dropwise to the reaction liquid over 15 minutes so that the internal temperature did not exceed 62° C., while washing with dichloromethane (25 ml). The reaction liquid was left to stand until it reached mom temperature and was stirred for 15 hours. The reaction liquid was concentrated and purified by silica gel column chromatography (elution solvent: ethyl acetate/heptane) to give the title compound (38 g).