CO[C:3]([O:6][CH3:7])([CH3:5])[CH3:4].OC[C@@H:10]1[NH:14][C:13](=[O:15])[CH2:12][CH2:11]1>C1(C)C=CC=CC=1.O.C1(C)C=CC(S(O)(=O)=O)=CC=1>[CH3:5][C:3]1([CH3:4])[N:14]2[C:13](=[O:15])[CH2:12][CH2:11][C@@H:10]2[CH2:7][O:6]1The reaction was equipped with a Dean-Stark then 2,2-dimethoxypropane (17.09 mL, 139 mmol) was added to a stirred mixture of (R)-(−)-5-(hydroxymethyl)-2-pyrrolidinone (5.353 g, 46.5 mmol) and p-toluenesulfonic acid monohydrate (0.126 g, 0.662 mmol) in toluene (100 mL). The reaction mixture was refluxed for 1.5 h and allowed to stir at room temperature overnight. Solvent was evaporated to afford (R)-3,3-dimethyltetrahydropyrrolo[1,2-c]oxazol-5(3H)-one (7.22 g, 100% yield) as a light yellow solid. 1H NMR (400 MHz, DMSO-d6) δ 4.18 (tt, J=8.8, 6.2 Hz, 1H), 4.00 (dd, J=8.1, 5.8 Hz, 1H), 3.40 (t, J=8.6 Hz, 1H), 2.69 (ddd, J=16.4, 12.1, 8.6 Hz, 1H), 2.33 (dd, J=16.3, 9.1 Hz, 1H), 2.02-2.11 (m, 1H), 1.73 (tt, J=12.1, 8.9 Hz, 1H), 1.53 (s, 3H), 1.33 (s, 3H). m/z (ESI, +ve) 156 (M+H).
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