(4R,5S)-(+)-4-Methyl-5-phenyl-2-oxazolidinone

To a solution of (1S,2R)-norephedrine (40 g, 0.26 mol) in toluene (400 mL) was added diethyl carbonate (37 mL, 0.32 mol). The mixture was heated to reflux (under Ar) while 40 mL of solvent was removed through the use of a Dean–Stark apparatus. The mixture was allowed to cool for 20 min, and then sodium methoxide (1 g) was added. Upon reheating, an EtOH/toluene azeotropic mixture was removed at 75–77 °C. After 3 h, the reaction was complete and the temperature of the mixture had increased to 125 °C. The mixture was left to stand at room temperature for 16 h, whereupon (4R,5S)-4-methyl-5-phenyloxazolidin-2-one (40.6 g) crystallized and could be collected. The solvent was removed from the filtrate in vacuo and the residue was redissolved in EtOAc (250 mL). This solution was washed with brine (50 mL) and a precipitate was removed by filtration. The solvent was then removed in vacuo and toluene (50 mL) was added to the residue. Removal of the toluene by distillation yielded oily crystals of the oxazolidinone, which were washed with Et2O to afford 4.5 g (total 45 g, 97%).