[H-].[Na+].[CH2:3]([O:10][C:11](=[O:20])[NH:12][C@@H:13]1[CH2:17][C:16](=[O:18])[NH:15][C:14]1=[O:19])[C:4]1[CH:9]=[CH:8][CH:7]=[CH:6][CH:5]=1.[CH2:21](Br)[C:22]1[CH:27]=[CH:26][CH:25]=[CH:24][CH:23]=1.CN(C=O)C>C1COCC1>[CH2:3]([O:10][C:11](=[O:20])[NH:12][C@@H:13]1[CH2:17][C:16](=[O:18])[N:15]([CH2:21][C:22]2[CH:27]=[CH:26][CH:25]=[CH:24][CH:23]=2)[C:14]1=[O:19])[C:4]1[CH:5]=[CH:6][CH:7]=[CH:8][CH:9]=11.2.2 (via two steps; 2nd step): A suspension of 48.4 mg of 60% NaH in 3 ml of THF was treated with 300 mg of (R)-(2,5-dioxo-pyrrolidin-3-yl)-carbamic acid benzyl ester at 0° C. followed by 161.3 μL of benzyl bromide. After 30 min the resulting precipitate was warmed to rt and treated with 3 ml of DMF to give after 15 min a solution which was stirred for 16 h at rt then quenched with 60 ml of H2O and extracted with 40 ml of toluene. The combined organic layers were dried over MgSO4 and concentrated to give 409 mg (74%) of the (R)-(2,5-dioxo-pyrrolidin-3-yl)-carbamic acid benzyl ester as white crystals; m.p. 145.1-145.5° C. Overall yield for the two step process: 78%.
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