A solution of (R)-4-benzyl-3-(2-(3-chlorophenyl)acetyl)oxazolidin-2-one (0.975 g, 2.96 mmol) in dry DCM (125 mL) was cooled to −78° C., and TiCl4 (3.10 mL, 3.10 mmol) was added. DIEA (0.566 mL, 3.25 mmol) was added to this stirring cold solution for 15 minutes. A solution of tert-butyl 5-methoxy-2,2-dimethylpyrrolidine-1-carboxylate (0.881 g, 3.84 mmol) in DCM (20 mL) was added to the cold mixture. The reaction was stirred for 15 minutes at −78° C. and then warmed to −10° C. (ice/acetone) and stirred for 3 hours. The reaction was quenched with NH4Cl, diluted with DCM (50 mL), water (50 mL), and the layers were separated. The aqueous layer was extracted with DCM (25 mL), dried (MgSO4) and concentrated to an oil. TLC (10% ethyl acetate/hexanes) shows desired product at Rf˜0.2. Purification by flash chromatography (5% ethyl acetate/hexanes-10% ethyl acetate/hexanes) gave (S)-tert-butyl 5-((S)-2-((R)-4-benzyl-2-oxooxazolidin-3-yl)-1-(3-chlorophenyl)-2-oxoethyl)-2,2-dimethylpyrrolidine-1-carboxylate (0.98 g, 1.86 mmol, 62.9% yield). HPLC, 254 nm, 100% purity, retention time=3.86 minutes.
