Regioselective synthesis of 3,3-bis(indolyl)propanoic acid derivatives by iron(III)-catalyzed hydroarylation of propynoic acid derivatives with indoles

Intermolecular hydroarylation of propynoic acid and its esters with indoles proceeded efficiently in acetic acid under a catalytic system of FeCl3/3AgOTf and afforded the corresponding 3,3-bis(indol-3yl)propanoic acids and their esters in high yields. In the case of 2-methylindole, 3-indolylacrylic acid and its ethyl ester were obtained in high yields. This iron-catalyzed hydroarylation showed a high regioselectivity at the 3-position of indoles and a high utility for the synthesis of bis(indol-3-yl) compounds, which are important for biological and pharmaceutical fields.