Synthesis
Step 1: Synthesis of 6-bromo-2,3-dihydro-1H-indole
To a mixed solution of 6-bromo-1H-indole (11.0 g, 56.1 mmol) in dichloromethane (180 mL) and trifluoroacetic acid (60 mL) was added triethylsilane (22.6 mL, 2.5 equiv). The reaction mixture was stirred at room temperature for 16 hours. Subsequently, additional dichloromethane (180 mL), concentrated ammonium hydroxide solution (about 50 mL) and water (200 mL) were added. The mixture was extracted with dichloromethane, the organic layers were combined, dried over anhydrous sodium sulfate and concentrated under reduced pressure. The residue was redissolved in a solvent mixture of ether and hexane (1:1, 100 mL), and a dioxane solution of 4N HCl (14 mL) was slowly added, and a precipitate was immediately observed to form. The precipitate was collected by filtration and the resulting solid was treated with saturated sodium bicarbonate solution. The mixture was again extracted with dichloromethane, the organic phases were combined, dried over anhydrous sodium sulfate, and concentrated under reduced pressure to afford 6-bromo-2,3-dihydro-1H-indole as a brown oil (ca. 10.0 g), which was used directly in the subsequent reaction without further purification.LC-MS analysis: m/z 195.9/197.9 [M-H]+, retention time 0.98 min.
References
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[2] ACS Medicinal Chemistry Letters, 2012, vol. 3, # 5, p. 373 - 377
[3] Patent: WO2016/25932, 2016, A1. Location in patent: Page/Page column 144
[4] Journal of Organic Chemistry, 2018, vol. 83, # 4, p. 2425 - 2437
[5] Organic and Biomolecular Chemistry, 2018, vol. 16, # 32, p. 5889 - 5898
