AN IMPROVED SYNTHESIS OF SUBSTITUTED BENZO[B]THIOPHEN-2-CARBOXYLIC ACIDS AND RELATED ACIDS

The oxidative cyclization of β-Aryl-α-mercaptoacrylic acids with chlorine in dry carbon tetrachloride rapidly gives the corresponding benzo[b]thiophen-2-carboxylic acids in high yield. This process is a considerable improvement on processes previously reported. The purity of the crude β-aryl-α-mercaptoacrylic acids can be determined by titration with iodine in ethanol and thus the crude intermediates can be cyclized without further purification by use of the calculated amount of chlorine. © 1969.