Imidazole → tert-butyl(3S)-3-{[tert-butyl(dimethyl)silyloxy]methyl}-5-oxo-1-[(1R)-1-phenylethyl]pyrrolidine-3-carboxylate

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To a solution of tert-butyl(3S)-3-hydroxymethyl-5-oxo-1-[(1R)-1-phenylethyl]pyrrolidine-3-carboxylate (8.23 g, 25.8 mmol) and imidazole (2.63 g, 38.7 mmol) in N,N-dimethylformamide (150 mL), tert-butyl dimethylsilyl chloride (4.66 g, 31.0 mmol) was added in an ice bath, and the mixture was stirred at room temperature for 4 hours. To the reaction mixture, saturated aqueous solution of ammonium chloride (300 mL) was added in an ice bath, and the mixture was extracted with diethylether (300 mL×2). The organic layer was washed with water (300 mL×2) and saturated aqueous solution of sodium chloride (200 mL), and dried with anhydrous magnesium sulfate. After filtration, the filtrate was concentrated under reduced pressure, and the residue was purified by silica gel column chromatography (elusion by hexane:ethyl acetate, 10:1→1:1) to obtain 7.98 g (71%) of the title compound as a colorless oily substance.

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