Synthesis
5-Nitro-1-benzothiophene-2-carboxylic acid (40 g, 179 mmol) was dissolved in quinoline (350 mL) under mechanical stirring followed by addition of copper powder (11.3 g, 179 mmol). The reaction mixture was heated to 190°C until complete gas release. After completion of the reaction, the mixture was cooled to room temperature and poured into crushed ice and acidified with concentrated hydrochloric acid. The resulting suspension was extracted with ethyl acetate and the organic layer was separated and washed sequentially with 2N hydrochloric acid, water and saturated brine. The organic layer was dried over anhydrous sodium sulfate and concentrated to give 5-nitrobenzothiophene (30.5 g, 95% yield). The structure of the product was confirmed by 1H NMR (DMSO-d6, 400 MHz) and LC-MS (electrospray): 1H NMR δ 8.85 (d, 1H), 8.31 (d, 1H), 8.18 (dd, 1H), 8.06 (d, 1H), 7.73 (d, 1H); LC-MS m/z = 180 [M + H]+.
References
[1] Bioorganic and Medicinal Chemistry, 2016, vol. 24, # 3, p. 403 - 427
[2] ACS Medicinal Chemistry Letters, 2016, vol. 7, # 8, p. 735 - 740
[3] ACS Medicinal Chemistry Letters, 2017, vol. 8, # 3, p. 338 - 343
[4] Patent: WO2006/66172, 2006, A1. Location in patent: Page/Page column 27
[5] Synthetic Communications, 1991, vol. 21, # 7, p. 959 - 964
