[CH3:1][C:2]1[CH:10]=[C:9]([CH3:11])[CH:8]=[C:7]2[C:3]=1[C:4](=[O:13])[C:5](=[O:12])[NH:6]2.[OH2:14]>C(O)(=O)C.[O-2].[O-2].[O-2].[Cr+6]>[CH3:1][C:2]1[C:3]2[C:4](=[O:13])[O:12][C:5](=[O:14])[NH:6][C:7]=2[CH:8]=[C:9]([CH3:11])[CH:10]=1To a stirred warm (60° C.) solution of 4,6-dimethyl-1H-indole-2,3-dione (2.0 g, 11.4 mM) in acetic acid (20 mL) was added in small portions chromium trioxide (6.6 g, 66 mM) while maintaining the temperature of the reaction mixture at 65°-70° C. The reaction mixture was then heated at 80° C. for one hour, cooled, poured into water (150 mL) and filtered to obtain the the title compound (0.67 g, 31%) as a light yellow solid; MS(CI): 192 (M+H).
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