Hydrochloric Acid → 6-Methoxybenzo[d]isothiazole-3-carboxylic acid

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Reaction Steps

To a solution of the amide (5.46 mmol) in methanol (100 mL) was added 10 N sodium hydroxide (12 mL). The mixture was heated at reflux for 12 h, cooled to rt, and was acidified to pH <2 by the slow addition of conc. hydrochloric acid. The organic layer was extracted with dichloromethane (2×) and was dried over sodium sulfate. The crude product was purified by chromatography (300/50/1 dichloromethane/methanol/formic acid) to provide 6-methoxy-1,2-benzisothiazole-3-carboxylic acid (89%) as a pink solid. The acid was coupled with 1,4-diazabicyclo[3.2.2]nonane according to procedure A.

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