Enabling Cyclopropanation Reactions of Imidazole Heterocycles via Chemoselective Photochemical Carbene Transfer Reactions of NHC-Boranes

Herein we report a site-selective cyclopropanation of N-heterocyclic carbene (NHC)-borane complexes via photochemical carbene transfer reactions. By subtle changes to the reaction conditions, this approach can be further extended toward the difunctionalization of NHC-boranes via cyclopropanation and the B-H insertion reaction. Further investigations in photochemical continuous-flow applications and synthetic transformations proved the utility of the method. Theoretical calculations and control experiments were performed to explain the observed selectivity.

Automated summary

A site-selective cyclopropanation of N-heterocyclic carbene (NHC)-borane complexes via photochemical carbene transfer reactions is reported in this study. The approach can also be extended to the difunctionalization of NHC-boranes through cyclopropanation and the B-H insertion reaction. Further investigations on photochemical continuous-flow applications and synthetic transformations demonstrate the utility of the method. Theoretical calculations and control experiments were conducted to explain the observed selectivity.