[OH:1][C@H:2]1[C@H:6]([CH3:7])[CH2:5][N:4]([C:8]([O:10][CH2:11][C:12]2[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=2)=[O:9])[CH2:3]1.[N+:18]([C:21]1[CH:29]=[CH:28][C:24]([C:25](O)=[O:26])=[CH:23][CH:22]=1)([O-:20])=[O:19].C1(P(C2C=CC=CC=2)C2C=CC=CC=2)C=CC=CC=1.CC(OC(/N=N/C(OC(C)C)=O)=O)C>C1COCC1>[CH3:7][C@H:6]1[C@@H:2]([O:1][C:25]([C:24]2[CH:23]=[CH:22][C:21]([N+:18]([O-:20])=[O:19])=[CH:29][CH:28]=2)=[O:26])[CH2:3][N:4]([C:8]([O:10][CH2:11][C:12]2[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=2)=[O:9])[CH2:5]1To a solution of enantiopure phenylmethyl (trans)-3-hydroxy-4-methyl-1-pyrrolidinecarboxylate (E1) (1 g, 4.25 mmol) in THF (21 mL) was added 4-nitrobenzoic acid (1.42 g, 8.5 mmol), triphenylphosphine (2.23 g, 8.5 mmol) and DIAD (1.7 mL, 8.5 mmol). The resulting solution was stirred overnight. Removal of the solvent under reduced pressure yielded the crude product which was purified by RP-HPLC yielding phenylmethyl (cis)-3-methyl-4-{[(4-nitrophenyl)carbonyl]oxy}-1-pyrrolidinecarboxylate (1.30 g, 79%). LCMS: (M+H)+: 385.0 (single unknown enantiomer).
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