Lithium tert-butoxide (LiOtBu, 160 mg, 2.00 mmol) and 5-methylindole (23.4 mg, 0.4 mmol) were added to a dry two-necked reaction vessel. The reaction vessel was evacuated by placing it under high vacuum conditions, followed by the passage of carbon dioxide gas (CO2 balloon). After addition of N,N-dimethylformamide (DMF, 2 mL), the reaction mixture was stirred at 100 °C for 24 hours. After completion of the reaction, the mixture was cooled to room temperature and the reaction was carefully quenched with 2N hydrochloric acid (HCl) solution. The reaction mixture was extracted several times with ethyl acetate (EtOAc, 5 x 5 mL). The organic phases were combined, washed sequentially with water (2 × 5 mL) and saturated saline (1 × 5 mL), and dried over anhydrous magnesium sulfate (MgSO4). The dried organic phases were concentrated under reduced pressure and the resulting residue was purified by preparative thin layer chromatography (TLC, Spreading agent: hexane/acetone=1:1) to afford the target product 5-methyl-1H-indole-3-carboxylic acid (153.0 mg, 95% yield) as a white solid.
