Synthesis
To a round-bottomed flask was added 6-bromo-1H-indole (14.88 g, 76 mmol) and anhydrous THF (150 ml) and stirred until completely dissolved to give a dark maroon solution. The flask was cooled in an ice-water bath and sodium hydride (60 wt% mineral oil dispersion, 3.64 g, 91 mmol) was added in batches over 15 min. The reaction mixture was stirred under ice bath for 20 min and then iodomethane (5.94 ml, 95 mmol) was added slowly through a syringe. Exothermic phenomenon was observed during the addition. After continued stirring for 20 min, the reaction mixture was concentrated under reduced pressure to remove the solvent. The residue was dissolved with saturated aqueous sodium bicarbonate solution and subsequently extracted with dichloromethane (3 x 50 ml). The organic phases were combined, dried with anhydrous sodium sulfate, filtered and concentrated to give the crude product. The crude product was purified by silica gel column chromatography (elution gradient: 0 to 40% ethyl acetate/heptane) to afford 6-bromo-1-methyl-1H-indole (14.44 g, 68.7 mmol, 91% yield) as a light-colored oil. The structure of the product was confirmed by 1H NMR (400 MHz, CDCl3): δ=7.51-7.46 (m, 2H), 7.24-7.19 (m, 1H), 7.03 (d, J=3.1Hz, 1H), 6.47 (dd, J=0.9, 3.1Hz, 1H), 3.77 (s, 3H).
References
[1] European Journal of Organic Chemistry, 2011, # 20-21, p. 3781 - 3793
[2] Helvetica Chimica Acta, 2006, vol. 89, # 5, p. 936 - 946
[3] Patent: WO2013/25883, 2013, A1. Location in patent: Page/Page column 41-42
[4] Journal of the American Chemical Society, 2013, vol. 135, # 30, p. 10978 - 10981
[5] ACS Medicinal Chemistry Letters, 2016, vol. 7, # 12, p. 1062 - 1067
