D-alaninol (8.65 g, 0.12 mmol) was dissolved in a mixed solvent of toluene and KOH aqueous solution (124 mL, 12.5% aqueous solution, 0.28 mmol) at 0 °C. Phosgene (72.7 mL, 20% toluene solution, 0.14 mmol) was added slowly dropwise, and the dropwise acceleration was controlled to maintain the internal temperature of the reaction system below 5 °C. After the dropwise addition, the reaction was continued to be stirred at 0 °C for 40 min. After completion of the reaction, the reaction mixture was concentrated to dryness under reduced pressure. The crude product was dissolved with industrial methanol, filtered to remove insoluble matter, and the filtrate was concentrated under reduced pressure to obtain the crude product. The crude product was purified by silica gel fast column chromatography (eluent gradient: 40-100% cyclohexane solution of ethyl acetate), and 10.4 g (90% yield) of (R)-4-methyl-2-oxazolidinone was finally obtained as a white solid. The product was characterized by 1H NMR (400 MHz, CDCl3): δ 6.00 (broad single peak, 1H), 4.50 (triple peak, J=6.5 Hz, 1H), 4.07-3.97 (multiple peaks, 1H), 3.95 (double dichotomous peaks, J=7.8,6.2 Hz, 1H), and 1.30 (dichotomous peak, J=6.1 Hz, 3H).
