Tetrabutylammonium Fluoride → tert-Butyl(3S)-3-hydroxymethyl-4-methyl-5-oxo-1-[(1R)-1-phenylethyl]pyrrolidine-3-carboxylate

Tert-butyl(3S)-3-{[tert-butyl(dimethyl)silyloxy]methyl}-4-methyl-5-oxo-1-[(1R)-1-phenylethyl]pyrrolidine-3-carboxylate (3.72 g, 8.31 mmol) was dissolved in tetrahydrofuran (70 mL), and tetrabutylammonium fluoride (12.5 mL, 1.0 mol/l solution in tetrahydrofuran, 12.5 mmol) was added dropwise in an ice bath. The mixture was stirred at the same temperature for 1 hour. After concentrating the mixture, saturated aqueous solution of ammonium chloride (200 mL) was added, and the mixture was extracted with ethyl acetate (200 mL×2). The organic layer was washed with saturated aqueous solution of sodium chloride (100 mL), and dried with anhydrous sodium sulfate. After filtration, the filtrate was concentrated under reduced pressure. The concentrate was purified by silica gel column chromatography (elusion by hexane:ethyl acetate=3:1→1:2) to obtain 1.87 g (67%) of the title compound as a white solid.