To a solution of 5-indolecarboxaldehyde (1.0 g, 6.9 mmol) in N,N-dimethylformamide (DMF, 15 mL) was added sodium hydride (303 mg, 60% oil dispersion, 7.59 mmol) in one portion. The reaction mixture was stirred at room temperature for 30 minutes. Subsequently, iodomethane (1.96 g, 13.8 mmol) was added to the reaction system and the mixture was continued to stir overnight. Upon completion of the reaction, ethyl acetate (200 mL) was added to dilute the reaction mixture, and the organic phase was washed sequentially with water (3 x 20 mL) and saturated saline (25 mL). The organic phase was dried with anhydrous magnesium sulfate, filtered and concentrated to afford 1-methyl-1H-indole-5-carbaldehyde as an orange oil (1.0 g, 91% yield). The product was characterized by 1H NMR (200 MHz, CDCl3): δ 10.05 (s, 1H), 8.09 (s, 1H), 7.90-7.80 (m, 1H), 7.35-7.15 (m, 2H), 6.85-6.80 (m, 1H), 3.95 (s, 3H).
