[I:1][C:2]1[CH:10]=[C:9]2[C:5]([C:6](=[O:12])[C:7](=[O:11])[NH:8]2)=[CH:4][CH:3]=1.[OH2:13]>C(O)(=O)C.C(OC(=O)C)(=O)C.[O-2].[O-2].[O-2].[Cr+6]>[I:1][C:2]1[CH:3]=[CH:4][C:5]2[C:6](=[O:12])[O:11][C:7](=[O:13])[NH:8][C:9]=2[CH:10]=1To a stirred warm (80° C.) solution of 6-iodo-1H-indole-2,3-dione (3.0 g, 11 mM) in acetic acid (10 mL) and acetic anhydride (10 mL) was added in small portions chromium trioxide (1.83 g, 18.3 mM) while maintaining the temperature of the reaction mixture at 80°-90° C. The reaction mixture was then heated at 80° C. for 10 min, cooled and poured into water. The resulting mixture was filtered and the collected solids dried to provide the title compound as a yellow solid (2.6 g, 81.8%); MS(CI): 290 (M+H).
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