[Br:1][C:2]1[CH:3]=[C:4]2[C:8](=[C:9]([C:11]([O:13][CH3:14])=[O:12])[CH:10]=1)[NH:7][CH2:6][CH2:5]2>O1CCCC1.[O-2].[O-2].[Mn+4]>[Br:1][C:2]1[CH:3]=[C:4]2[C:8](=[C:9]([C:11]([O:13][CH3:14])=[O:12])[CH:10]=1)[NH:7][CH:6]=[CH:5]2Methyl 5-bromo-2,3-dihydro-1H-indole-7-carboxylate (6.5 g, 25 mmol) was dissolved in tetrahydrofuran (100 mL). Activated manganese dioxide (5 μm particle size, 22 g, 250 mmol) was added and the mixture stirred at room temperature for 16 hours. A further 22 g of activated manganese dioxide was added and the reaction stirred for 96 hours. The reaction was then filtered through celite and concentrated in vacuo to give 5.1 g (80%) of the title compound as a beige solid.
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