Synthesis
Under nitrogen protection, 5-methoxybenzo[b]thiophene (Example 20a, 1.5 g, 9.14 mmol, 1.0 eq.) was dissolved in dichloromethane (20 mL) and cooled to -10 °C. Boron tribromide (1M in DCM, 36.6mL, 36.6mmol, 4.0 equiv) was added slowly and dropwise. The reaction was kept at this temperature and stirred for 30 minutes and then slowly warmed to room temperature to continue the reaction for 1 hour. After completion of the reaction, the reaction was quenched with methanol at -5 °C. Extraction was carried out with dichloromethane (50 mL) and water, the organic layer was washed with saturated aqueous sodium bisulfite, dried over anhydrous sodium sulfate and concentrated. The residue was purified by fast column chromatography (petroleum ether: ethyl acetate = 4:1) to afford the target product benzo[b]thiophen-5-ol (Example 20b, 1 g, 73% yield, yellow solid). Mass spectrometry analysis showed [M + 1] + = 151.0.
References
[1] Bioorganic and Medicinal Chemistry Letters, 2012, vol. 22, # 8, p. 2948 - 2950
[2] Patent: WO2017/218960, 2017, A1. Location in patent: Paragraph 00463; 00466
[3] Journal of Heterocyclic Chemistry, 2001, vol. 38, # 5, p. 1025 - 1030
[4] Journal of the American Chemical Society, 2013, vol. 135, # 20, p. 7450 - 7453
[5] Patent: US2010/279983, 2010, A1. Location in patent: Page/Page column 24
