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NaOH solution (10 mL, 100 mmol) was added to a solution of 6- bromobenzo[b]thiophene-3-carboxamide (1.20 g, 4.67 mmol) in MeOH (80 mL). The mixture was heated at reflux overnight. After cooling, the mixture was acidified with 2N HCl. The resulting precipitate was filtered and dried to give 6-Bromobenzo[d]isothiazole-3-carboxylic acid (1.10 g, 91percent) as a solid.

[1] Patent: WO2009/89462, 2009, A1. Location in patent: Page/Page column 81
[2] Patent: WO2007/98169, 2007, A1. Location in patent: Page/Page column 66
[3] Patent: WO2007/100880, 2007, A1. Location in patent: Page/Page column 79