Direct construction of 2,3-unsubstituted benzofurans and benzothiophenes via a metal-free catalyzed intramolecular Friedel-Crafts reaction

A highly effective and straightforward method for the construction of 2,3-unsubstituted benzofurans and benzothiophenes by the intramolecular Friedel-Crafts reaction has been developed. This phosphoric acid-catalyzed method exhibits good functional group tolerance for both electron-withdrawing groups and electron-donating groups. We have successfully obtained benzofuran and benzothiophene derivatives with various substituents, and the yield was up to 94%. The development of this reaction provides a simple and efficient strategy for the construction of benzofuran and benzothiophene skeleton compounds.