[NH:1]1[C:9]2[C:4](=[CH:5][CH:6]=[C:7]([C:10]([OH:12])=[O:11])[CH:8]=2)[CH:3]=[CH:2]1.[H-].[Na+].[CH3:15]I.[OH-].[K+]>CN(C=O)C.O>[CH3:15][N:1]1[C:9]2[C:4](=[CH:5][CH:6]=[C:7]([C:10]([OH:12])=[O:11])[CH:8]=2)[CH:3]=[CH:2]1In a similar manner to Step 1 of Reference Example 12, indole-6-carboxylic acid (200 mg, 1.24 mmol) was dissolved in DMF (2 mL), and the solution was treated with 60% sodium hydride-mineral oil dispersant (109 mg, 2.71 mmol), methyl iodide (0.258 mL, 0.410 mmol) and 4 mol/L aqueous potassium hydroxide solution (2 mL). The reaction mixture was added with water and separated into aqueous layer and organic layer, and the organic layer was removed. The aqueous layer was added with 1 mol/L hydrochloric acid to adjust the pH to 1, followed by stirring at room temperature for 1 hour. The obtained solid was collected by filtration and dried under reduced pressure to obtain 1-methylindole-6-carboxylic acid (154 mg, yield 71%).
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