Synthesis
Step A: A solution of pyridinium bromide (10.99 g, 34.3 mmol) in pyridine (200 mL) was slowly added dropwise to a solution of pyridinium bromide (10.99 g, 34.3 mmol) in pyridine (200 mL) of 5-nitroindole (5.00 g, 30.8 mmol) at -40 °C and under nitrogen protection. After the dropwise addition was completed, the reaction mixture was continued to be stirred at 0°C for 5 minutes. Subsequently, the reaction mixture was diluted with water (200 mL) at 0 °C and extracted with ether (200 mL). The organic layer was washed sequentially with 6 M hydrochloric acid (300 mL), 5% sodium bicarbonate solution (300 mL) and saturated saline (300 mL). The organic phase was dried over anhydrous magnesium sulfate and concentrated under reduced pressure to remove the solvent to give 3-bromo-5-nitroindole as a yellow powder with 80% purity containing 20% 5-nitroindole (6.80 g, 74% yield).
References
[1] Tetrahedron Letters, 2003, vol. 44, # 20, p. 3927 - 3930
[2] Bioorganic and Medicinal Chemistry, 2007, vol. 15, # 17, p. 5965 - 5980
[3] RSC Advances, 2016, vol. 6, # 93, p. 90031 - 90034
[4] Tetrahedron Letters, 2015, vol. 56, # 9, p. 1096 - 1098
[5] Patent: WO2006/19831, 2006, A1. Location in patent: Page/Page column 415
