Copper‐Catalyzed Cyclopropanation Reaction of Indoles through Diyne Cyclization

Comprehensive Summary Transition metal‐catalyzed cyclopropanation reactions of indoles are generally limited to diazo compounds. Herein, an efficient copper‐catalyzed cyclopropanation reaction of indoles with N ‐propargyl ynamides is demonstrated, allowing for practical and atom‐economic construction of valuable cyclopropa[ b ]indolines in generally moderate to excellent yields under mild reaction conditions. Thus, this reaction constitutes a new way for cyclopropanation of indoles involving vinyl cations generated from diyne cyclization as key intermediates. Moreover, such an asymmetric cyclopropanation of indoles via chiral copper catalysis has also been realized. In addition, the formal C(sp 2 )–H functionalization of indoles is achieved by a one‐pot copper‐catalyzed diyne cyclization followed by proton acid‐mediated ring‐opening of cyclopropanes.