[C:1]([O:5][C:6]([N:8]1[C:12](=[O:13])[CH2:11][CH2:10][C@H:9]1[C:14]([OH:16])=[O:15])=[O:7])([CH3:4])([CH3:3])[CH3:2].[CH2:17](Br)[C:18]1[CH:23]=[CH:22][CH:21]=[CH:20][CH:19]=1.C(=O)([O-])[O-].[K+].[K+]>CN(C=O)C>[C:1]([O:5][C:6]([N:8]1[C:12](=[O:13])[CH2:11][CH2:10][CH:9]1[C:14]([O:16][CH2:17][C:18]1[CH:23]=[CH:22][CH:21]=[CH:20][CH:19]=1)=[O:15])=[O:7])([CH3:4])([CH3:2])[CH3:3]A suspension containing (2S)5-oxo-pyrrolidine-1,2-dicarboxylic acid 1-tert-butyl ester (10.00 g, 0.044 mol, 1.0 equivalent), benzyl bromide (7.88 g, 0.046 mol, 1.05 equivalents), and potassium carbonate (15.20 g, 0.11 mol, 2.5 equivalents) in DMF (200 ml) was allowed to stir at 65° C. overnight. The reaction was allowed to cool to room temperature and the mixture was filtered through Celite. The solid was rinsed with ethyl acetate (100 ml) and the resulting filtrate was partitioned between ethyl acetate and saturated brine solution. The organic layer was washed with saturated brine (3×100 ml), dried over anhydrous Na2SO4 and concentrated in vacuo. The crude, colorless oil was chromatographed on silica to afford 5-oxo-pyrrolidine-1,2-dicarboxylic acid 2-benzyl ester 1-tert-butyl ester as a colorless oil (8.20 g, 0.026 mol, 59% yield). Analysis H1 NMR (400 MHz, CDCl3): 7.36 (5H, broad s), 5.20 (2H, d), 4.64 (1H, dd), 2.44–1.96 (4H, m), 1.41 (9H, s). MS (LC-MS): Calculated for C17H21NO5 319.14, found 320.19 (M+H)+.
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