[C:1]([O:4][C:5]1[CH:13]=[CH:12][CH:11]=[C:10]2[C:6]=1[CH2:7][C:8](=[O:14])[NH:9]2)(=[O:3])[CH3:2].C(=O)([O-])[O-].[Na+].[Na+].[C:21](OC(=O)C)(=[O:23])[CH3:22]>O1CCCC1>[C:21]([N:9]1[C:10]2[C:6](=[C:5]([O:4][C:1](=[O:3])[CH3:2])[CH:13]=[CH:12][CH:11]=2)[CH2:7][C:8]1=[O:14])(=[O:23])[CH3:22]To a mixture of 4-(acetyloxy)-1,3-dihydro-2H-indol-2-one (J. Med. Chem., 38:2802–2808, 1995; 1.44 g, 7.5 mmol) and sodium carbonate (5.3 g, 50 mmol) in tetrahydrofuran (50 mL) is added acetic anhydride (4.3 mL, 45 mmol). The mixture is stirred at ambient temperature for 18 hours, and partitioned between ethyl acetate and water. After drying (magnesium sulfate), the solvent is removed in vacuo. The crude material is preadsorbed on silica gel (10 g), and purified by flash chromtography (90 g SiO2, 10% ethyl acetate:hexane to 70% ethyl acetate:hexane, linear gradient over 30 minutes) to provide 480 mg (27%) of acetic acid 1-acetyl-2-oxo-2,3-dihydro-1H-indol-4-yl ester as a white solid.
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