[H-].[Na+].[CH2:3]([O:10][C:11]([N:13]1[CH2:17][C@H:16]([OH:18])[CH2:15][C@H:14]1[C:19]([OH:21])=[O:20])=[O:12])[C:4]1[CH:9]=[CH:8][CH:7]=[CH:6][CH:5]=1.I[CH3:23]>C1COCC1.C(=O)(O)[O-].[Na+]>[CH2:3]([O:10][C:11]([N:13]1[CH2:17][C@H:16]([O:18][CH3:23])[CH2:15][C@H:14]1[C:19]([OH:21])=[O:20])=[O:12])[C:4]1[CH:9]=[CH:8][CH:7]=[CH:6][CH:5]=1
Sodium hydride (543 mg, 22.6 mmol, 2.00 equiv) was carefully added to a solution of (2S,4R)-1-[(benzyloxy)carbonyl]-4-hydroxy-2-pyrrolidinecarboxylic acid (3-1, 3.00 g, 11.3 mmol, 1 equiv) in THF (100 mL) at 0° C., and resulting mixture was stirred for 20 minutes. Iodomethane (2.11 mL, 33.9 mmol, 3.00 equiv) was added, and the mixture was warmed to 23° C. and stirred for 20 h. The reaction mixture was then diluted with saturated sodium bicarbonate solution washed with ethyl acetate (2×100 mL). The aqueous layer was then acidified with 1 N HCl solution to pH 3 and extracted with ethyl acetate (100 ml). This organic layer was then dried over sodium sulfate and concentrated to provide (2S,4R)-1-[(benzyloxy)carbonyl]-4-methoxy-2-pyrrolidinecarboxylic acid (3-2) as a light yellow oil. 1H NMR (400 MHz, CDCl3) major rotamer: δ7.40-7.25 (br m, 5H), 5.20 (s, 2H), 4.52 (t, 1H, J=7.4 Hz), 4.00 (m, 1H), 3.67 (dd, 1H, J=11.4, 2.8 Hz), 3.57 (dd, 1H, J=11.4, 4.6 Hz), 3.32 (s, 3H), 2.34 (m, 2H).
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