Synthesis
Step 1. 4-Bromoindole (5.00 mL, 39.9 mmol) was dissolved in a solvent mixture of acetic acid (5.00 mL, 87.9 mmol) and methanol (25.0 mL, 617 mmol) and the reaction system was cooled to 0°C. Sodium cyanoborohydride (7.52 g, 0.120 mol) was slowly added under stirring, followed by a slow warming of the reaction mixture to room temperature over 1 hour. After completion of the reaction, the mixture was concentrated and neutralized with saturated aqueous sodium bicarbonate solution. Extraction was carried out using ether and ethyl acetate, the organic phases were combined and washed with brine, dried over anhydrous sodium sulfate, filtered and concentrated to give 4.11 g (52% yield) of 4-bromo-2,3-dihydro-1H-indole.
References
[1] Journal of Medicinal Chemistry, 2014, vol. 57, # 6, p. 2462 - 2471
[2] Patent: US2007/265258, 2007, A1. Location in patent: Page/Page column 24
[3] Patent: WO2007/100880, 2007, A1. Location in patent: Page/Page column 81
[4] Journal of Medicinal Chemistry, 2011, vol. 54, # 1, p. 166 - 178
[5] Organic Letters, 2013, vol. 15, # 22, p. 5662 - 5665
