[C:1]([O:5][C:6]([N:8]1[CH2:12][CH2:11][C@H:10]([CH:13](C(O)=O)[C:14]([OH:16])=[O:15])[CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2]>C1(C)C=CC=CC=1.CS(C)=O.CC(OC)(C)C>[C:1]([O:5][C:6]([N:8]1[CH2:12][CH2:11][C@H:10]([CH2:13][C:14]([OH:16])=[O:15])[CH2:9]1)=[O:7])([CH3:4])([CH3:2])[CH3:3]A suspension of (R)-2-(1-(tert-butoxycarbonyl)pyrrolidin-3-yl)malonic acid (15 g, 55 mmol) in toluene (150 mL) and dimethylsulfoxide (2 mL) was heated to reflux for a period of 2 h. The mixture was allowed to reach ambient and diluted with MTBE (150 mL). The organic solution was washed with 10% aqueous citric acid (2×200 mL), and the solvent was removed under vacuum to afford 11.6 g of (R)-2-(1-(tert-butoxycarbonyl)-pyrrolidin-3-yl)acetic acid as an off-white solid (92% yield). 1H NMR (DMSO-d6, 400 MHz): δ 12.1 (s, 1H); 3.36-3.48 (m, 1H); 3.20-3.34 (m, 1H); 3.05-3.19 (m, 1H, 2.72-2.84 (m, 1H); 2.30-2.42 (m, 1H), 2.22-2.30 (m, 2H); 1.85-2.00 (m, 1H); 1.38-1.54 (m, 1H), 1.35 (2, 9H).
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