Visible-Light Photocatalytic Functionalization of Aryl Chlorides and Fluorides

Aryl chlorides and fluorides are inexpensive and readily available feedstocks; however, the high bond dissociation energies and low polarizability of C_Ar─X (Cl, F) bonds have long posed significant challenges to classical thermal activation, which is often harsh and poorly compatible with functional groups. Visible-light photocatalysis has emerged as a powerful strategy that overcomes these limitations by leveraging single-electron transfer to highly reactive radical intermediates under mild conditions. This review provides a mechanistically guided overview of recent advances in photocatalytic functionalization of aryl chlorides and fluorides, encompassing oxidative and reductive radical activation, radical-polar crossover, homolytic aromatic substitution, and synergistic photoredox/transition-metal catalysis.