A novel base-promoted intramolecular cyclization approach for the synthesis of benzofurans, benzothiophenes and indoles

A facile transition-metal-free method for the synthesis of benzofuran was developed via potassium t-butoxide promoted intramolecular cyclization of o-bromobenzylketones. This method showed a wide range of substrate tolerability affording substituted benzofurans in moderate to good isolated yields. In addition, thio-ketones and imines could also be converted to corresponding benzothiophenes and indoles applying this approach. The practicability of this method is further proved by a four-step total synthesis of natural product coumestrol.