2,2-Dimethoxypropane → 3H,5H-Pyrrolo[1,2-c]oxazol-5-one, tetrahydro-3,3-dimethyl-, (R)-

To a mixture consisting of (R)-5-hydroxymethyl-2-pyrrolidinone (50.0 g, 434 mmol) in 2,2-dimethoxypropane (533 mL, 4300 mmol) was added camphorsulfonic acid (2.85 g, 10.8 mmol). The stirring mixture was brought to reflux at 88° C. for 1.5 hours, while removing methanol by distillation. The reaction mixture was subsequently heated to 95° C. for one hour, cooled to room temperature, treated with triethylamine (5 mL), and stirred for 5 minutes. The mixture was then diluted with hexanes-ethyl acetate (500 mL, 1:3 v/v) and washed sequentially with a 50% aqueous solution of sodium chloride and a saturated aqueous solution of sodium chloride. The organic phase was dried over sodium sulfate, filtered, and concentrated. The residue was purified by crystallization from hexanes to afford the title compound as white crystalline solid (30.48 g, 45%); TLC Rf 0.4 (solvent system: 5:95 v/v methanol:dichloromethane) MS (ESI+) m/z 156.1 (M+H)+, 178.1 (M+Na)+; 1H-NMR (CDCl3) δ 4.3-4.2 (m, 1H), 4.1 (dd, 1H), 3.5 (t, 1H), 2.9-2.7 (m, 1H), 2.6-2.5 (m, 1H), 2.2-2.1 (m, 1H), 1.9-1.7 (m, 1H), 1.7 (s, 3H), 1.5 (s, 3H).