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 cyclopropabbenzofurans in generally moderate to excellent yields. Furthermore, preliminary studies on asymmetric catalysis reveal that the desired chiral cyclopropabbenzofurans could be synthesized with good to excellent ee's.
Xu et al. (Tue,) studied this question.