Photoredox/copper-catalyzed formal cyclopropanation of olefins

Abstract

The construction of cyclopropanes via visible-light-driven transformations plays an important role in organic synthesis. Among these transformations, intermolecular atom transfer radical addition (ATRA) with alkenes followed by intramolecular nucleophilic substitution can be used to efficiently form cyclopropanes. However, electron-deficient aromatic rings are prone to being attacked by nucleophilic alkyl radicals in this transformation, which significantly limits the diversity of cyclopropanes. Herein, electron-rich copper catalysts as captors of alkyl radicals were introduced to regulate the regioselectivity of the reaction, avoiding this limitation. This transformation displays broad functional group tolerance, including substrates bearing ketones, esters, amides, sulfones, perfluoroalkanes, and especially aromatic groups that would be inaccessible with previous methods. Mechanism studies show that this transformation involves intermolecular atom transfer radical addition and intramolecular nucleophilic substitution, and the copper catalysts play a key role.