A formal [3 + 2]-cycloaddition reaction of 2Hazirines with nitrosoarenes has been achieved under irradiation by visible light with the assistance of organic dye photoredox catalyst. This method utilizes nitrosoarenes as efficient radical acceptors and provides a green and powerful method for a series of biologically important 1,2,4-oxadiazole derivatives in moderate to good yields.

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.

Cyclopropanes are one of the most important strained rings existing in various pharmaceutical products and secondary metabolites. They are also widely used in total synthesis of natural products, medicinal chemistry, and materials science. In the past years, photochemical cyclopropanation has been gradually developed as a robust and attractive synthetic method to prepare diverse cyclopropane backbones. In this review, we summarize recent advances in the visible light‐mediated cyclopropane synthesis, especially in photochemical cyclopropanation using carbene transfer strategy and photocatalytic radical cyclopropanation reactions.