Rhodium-Catalyzed Asymmetric Cyclopropanation of Indoles with N-Triftosylhydrazones.

Herein we report a general rhodium-catalyzed asymmetric intermolecular dearomative cyclopropanation of indoles using trifluoromethyl N-triftosylhydrazones as carbene precursors. The reaction enables the rapid construction of diverse cyclopropane-fused indolines bearing a trifluoromethylated quaternary stereocenter with high enantioselectivity (up to 99 % ee). This mild method exhibits broad substrate scope, tolerating various functional groups, and can even be utilized for the late-stage diversification of complex bioactive molecules. DFT calculations suggest that the formation of a key zwitterionic intermediate is responsible for the chiral induction. Overall, this approach opens up new possibilities for asymmetric cyclopropanation of challenging aromatic heterocyclic compounds.