Selective Para-Functionalization of Aromatic C(sp2)─H Bonds via Atomically Dispersed Photocatalysis.

Direct functionalization of aromatic C─H bonds is crucial in organic synthesis due to their wide applications in pharmaceutical chemistry and materials engineering, yet precise site selectivity remains challenging. Traditional methods often rely on electrophilic aromatic substitution or transition metal catalysis with directing group strategies, which can result in product mixtures or require pre-installed functional groups. In this respect, recent advances using single-atom catalysts (SACs) are promising due to their enhanced reactivity and selectivity. This study introduces a robust catalytic system for undirected para-C─H functionalization of electron-rich arenes by using an atomically dispersed copper-based photocatalyst. The method bypasses the requirement of pre-installed directing groups, achieving site-selective functionalization through an η2 interaction with arenes under mild conditions, with a broad substrate scope, and excellent catalyst recyclability. Furthermore, this approach offers a novel method for incorporating functional groups into complex drug molecules, which is crucial in the synthesis of pharmaceuticals and natural products.