Regioselective and Versatile Synthesis of Indoles via Intramolecular Friedel–Crafts Heteroannulation of Enaminones

Abstract

A new approach is described for the synthesis of substituted indoles 5, through an intramolecular and regioselective Friedel–Crafts cyclization of enaminones 6a–h catalyzed by Lewis acids. Compounds 6 were prepared from the 2-anilinocarbonyl compounds 7, by treatment with DMFDMA under thermal or microwave (MW) irradiation conditions. An alternative and shorter one-pot two-step synthesis of indoles 5 was achieved starting from compounds 7 and promoted by MW radiation, including the elusive 2-acetylindoles 5i–m.