5194-37-6

Step 3: (0367) To a 500 mL single neck flask was added ethyl 4-bromo-1-benzothiophene-2-carboxylate (20 g, 70.4 mmol), tetrahydrofuran (120 mL) and water (100 mL). Aqueous 4 N sodium hydroxide (40 mL) was added slowly with stirring, followed by heating the reaction mixture to 70 °C with continuous stirring for 1 hour. After completion of the reaction, the reaction mixture was extracted with ethyl acetate (70 mL x 2). The pH of the aqueous phase was adjusted to 12 with concentrated hydrochloric acid and the precipitated solid was filtered and dried to give 4-bromobenzo[b]thiophene-2-carboxylic acid (16 g, yield: 88%).

[1] Indian Journal of Chemistry, Section B: Organic Chemistry Including Medicinal Chemistry, 1984, vol. 23, # 1, p. 38 - 41
[2] Patent: US2017/158680, 2017, A1. Location in patent: Paragraph 0361; 0366; 0367