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[b]benzofurans in generally moderate to excellent yields. Furthermore, preliminary studies on asymmetric catalysis reveal that the desired chiral cyclopropa[b]benzofurans could be synthesized with good to excellent ee's.