Synthesis
5-Methoxyindole (1.5 g, 10.2 mmol) was dissolved in acetic acid (20 mL) at 25 °C, followed by the addition of sodium cyanoborohydride (0.77 g, 12.2 mmol) in batches. After the reaction lasted for 1 h, the pH of the reaction solution was adjusted to 9-10 with 20% sodium hydroxide solution for neutralization. The reaction mixture was extracted with ethyl acetate (50 mL) and the organic phase was separated and dried over anhydrous sodium sulfate. The dried organic phase was filtered and the filtrate was concentrated by rotary evaporation. Finally, 5-methoxyindoline was purified by column chromatography (eluent: petroleum ether/ethyl acetate, 10:1, v/v) to afford 5-methoxyindoline as a brown solid (1.46 g, 95.9% yield).
References
[1] Organic Letters, 2011, vol. 13, # 19, p. 5124 - 5127
[2] Chemical Communications, 2013, vol. 49, # 63, p. 7052 - 7054
[3] Patent: CN105367474, 2016, A. Location in patent: Paragraph 0194; 0195; 0196; 0197
[4] Journal of Medicinal Chemistry, 1997, vol. 40, # 4, p. 479 - 485
[5] Patent: EP1223170, 2002, A1
