C[O:2][C:3]1[CH:11]=[CH:10][CH:9]=[C:8]2[C:4]=1[CH:5]=[C:6]([C:13]([OH:15])=[O:14])[N:7]2[CH3:12].B(Br)(Br)Br.[OH-].[Na+]>ClCCl>[OH:2][C:3]1[CH:11]=[CH:10][CH:9]=[C:8]2[C:4]=1[CH:5]=[C:6]([C:13]([OH:15])=[O:14])[N:7]2[CH3:12]To 4-methoxy-1-methyl-1H-indole-2-carboxylic acid (2.92 mmol, 600 mg) in dichloromethane (30 ml) under a nitrogen atmosphere was added boron tribromide (6.96 mmol, 671 μl, 1745 mg) keeping the temperature at 0 to 5° C. After stirring the reaction mixture at room temperature for three hours it was treated with 2N aqueous sodium hydroxide (to give a pH of 9) and stirred for additional 10 minutes. The aqueous phase was separated and neutralized with 2 N hydrochloric acid at 0° C. (pH between 6 and 7). The precipitate thus obtained was collected by filtration and coevaporated with toluene twice to yield 4-hydroxy-1-methyl-1H-indole-2-carboxylic acid (223 mg).
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