Decarboxylation of a benzo[b] thiophene-2-carboxylic acid

5-Hydroxy-3-methylbenzob]thiophene-2-carboxylic acid can be decarboxylated by refluxing with 48% hydrobromic acid for 30 minutes. Yield and quality of the product are better than for the previously used copper-quinoline decarboxylation. The 5-methoxy analog of the above acid is stable to decarboxylation under these conditions; however, it demethylates readily under the reaction conditions, and the phenol thus afforded decarboxylates.