Triethylamine (1.3 mL, 9.1 mmol) was added to (S)-3-phenylbutyric acid (1.0 g, 6.1 mmol) in anhydrous tetrahydrofuran (60 mL) at −78° C. followed by the dropwise addition of pivaloyl chloride (0.83 ml, 6.7 mmol) to give a white solid. The reaction was allowed to warm to room temperature for 10 minutes then cooled back down to −78° C. In a separate flask, n-butyllithium (4.6 mL, 11.6 mmol, 2.5 M F in hexanes) was added to (S)-(+)-4-phenyl-2-oxazolidinone (2.0 g, 12.2 mmol) in anhydrous tetrahydrofuran at −78° C. and allowed to stir for 10 minutes. The lithiated oxazolidinone was transfered via cannula to the mixed anhydride at −78° C. and stirring continued for 2 hours. The reaction was quenched with water (25 mL) and extracted with ethyl acetate. The combined extracts were washed with water, brine and dried over sodium sulfate. The crude product was purified by chromatography over silica gel eluted with 2:3 ethyl acetate/hexanes and the resulting solid was recrystallized from ethyl acetate/hexanes to afford (S)-4-phenyl-3-((S)-3-phenyl-butyryl)-oxazolidin-2-one (1.63 g, 88% yield).
