Copper-Catalyzed Dearomative Cyclopropanation of Benzofurans with Diynes via Vinyl Cations

Dearomative cyclopropanation of benzofurans is a powerful strategy for the assembly of valuable O-heterocycles. However, transition metal-catalyzed cyclopropanation of benzofurans is generally limited to diazo compounds. Herein, a copper-catalyzed dearomative cyclopropanation of benzofurans with diynes via vinyl cations is described, enabling the atom-economical and practical synthesis of various cyclopropa[<i>b</i>]benzofurans in generally moderate to excellent yields. Furthermore, preliminary studies on asymmetric catalysis reveal that the desired chiral cyclopropa[<i>b</i>]benzofurans could be synthesized with good to excellent ee's.