Benzo[b] thiophene derivatives. XXII. Synthesis of the isomeric 5-methyl-6-methoxy- and 5-methoxy-6-methylbenzo[b] thiophene-2-carboxylic acids

The two isomeric benzob] thiophene-2-carboxylie acids having methyl and methoxy groups at positions 5 and 6 have been prepared and characterized. Both acids have been decarboxylated to the corresponding isomeric 5,6-disubstituted benzob]thophenes, and esterified to their methyl esters. The intermediate rhodanines, α-mercaptocinnamic acids and corresponding disulfides are described. An unusual by-product in the oxidative cyclization of β-3-methyl-4-methoxyphenyl-α-mercaptoacrylic acid with iodine is shown to be trans-3-methyl-4-methoxycinnamic acid, which can also be formed directly from the mercaptoacrylic acid by reduction with hydrogen iodide.