To a dry Schlenk tube containing DMSO-d6 (1 mL) and cesium carbonate (33 mg, 0.1 mmol) was added (S)-1a (0.1114 mL, 1 mmol). The reaction mixture was frozen in a liquid nitrogen bath (-196 °C), followed by evacuation to remove air and replacement with CO2 gas. After thawing to 25 °C, a balloon (1 L) containing CO2 was connected to the reaction tube. The reaction system was stirred at 150°C for 24 hours. Upon completion of the reaction, the crude product was analyzed by 1H NMR and the yield was calculated using the internal standard N,N-dimethylformamide as reference. Subsequently, DMSO-d6 was removed by distillation under reduced pressure conditions (6 mmHg, 50 °C).The residue was purified by silica gel column chromatography (eluent: hexane/ethyl acetate, 3:1) to afford the target product (S)-4-isopropyloxazolidin-2-one ((S)-2a) as a white solid in 80% isolated yield (103.3 mg, 0.80 mmol).
