D-Proline → (2R)-1-Methacryloylpyrrolidin-2-carboxylic Acid

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D-Proline, 14.93 g, 0.13 mol) was dissolved in 71 mL of 2 N NaOH and cooled in an ice bath; the resulting alkaline solution was diluted with acetone (71 mL). An acetone solution (71 mL) of methacryloyl chloride (13.56 g, 0.13 mol) and 2N NaOH solution (71 mL) were simultaneously added over 40 min to the aqueous solution of D-proline in an ice bath. The pH of the mixture was kept at 10-11° C. during the addition of the methacryloyl chloride. After stirring (3 h, room temperature), the mixture was evaporated in vacuo at a temperature at 35-45° C. to remove acetone. The resulting solution was washed with ethyl ether and was acidified to pH 2 with concentrated HCl. The acidic mixture was saturated with NaCl and was extracted with EtOAc (100 mL×3). The combined extracts were dried over Na2SO4, filtered through Celite, and evaporated in vacuo to give the crude product as a colorless oil. Recrystallization of the oil from ethyl ether and hexanes afforded 16.2 g (68%) of the desired compound as colorless crystals: mp 102-103° C. (lit. [214] mp 102.5-103.5° C.); the NMR spectrum of this compound demonstrated the existence of two rotamers of the title compound. 1H NMR (300 MHz, DMSO-d6) δ 5.28 (s) and 5.15 (s) for the first rotamer, 5.15 (s) and 5.03 (s) for the second rotamer (totally 2H for both rotamers, vinyl CH2), 4.48-4.44 for the first rotamer, 4.24-4.20 (m) for the second rotamer (totally 1H for both rotamers, CH at the chiral canter), 3.57-3.38 (m, 2H, CH2), 2.27-2.12 (1H, CH), 1.97-1.72 (m, 6H, CH2, CH, Me); 13C NMR (75 MHz, DMSO-d6) δ for major rotamer 173.3, 169.1, 140.9, 116.4, 58.3, 48.7, 28.9, 24.7, 19.5: for minor rotamer 174.0, 170.0, 141.6, 115.2, 60.3, 45.9, 31.0, 22.3, 19.7; IR (KBr) 3437 (OH), 1737 (C═O), 1647 (CO, COOH), 1584, 1508, 1459, 1369, 1348, 1178 cm−1; [α]D26+80.8° (c=1, MeOH); Anal. Calcd. for C9H13NO3: C, 59.00; H, 7.15; N, 7.65. Found: C, 59.13; H, 7.19; N, 7.61.

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