The recent achievements of redox-neutral radical C-C cross-coupling enabled by visible-light

Visible-light photoredox catalysis has been esteemed as one sustainable and attractive synthetic tool. In the past four years, a new yet challenging trend, visible-light-driven redox-neutral radical C-C crosscoupling involving putative radical intermediates, has been booming rapidly. Its advent brings a powerful platform to achieve non-classical C-C connections, and should lead to fundamental changes in retrosynthetic analysis. In this tutorial review, we highlight the recent achievements of visible-light-mediated redox-neutral radical C(sp(3))-C(sp(2)), C(sp(3))-C(sp), and C(sp(3))-C(sp(3)) bond formation, opening a new window for C-C cross-coupling through the photoredox electron shuttling cycle between two coupling partners. While radical-radical coupling steered by the persistent radical effect was proposed as a rational explanation for the redox-neutral photoredox events, alternative kinetically driven chain propagation and radical addition pathways cannot be ruled out. This tutorial review aims to highlight the recent achievements of photoredox-neutral radical C-C coupling in synthetic chemistry.