Mild and metal-free Birch-type hydrogenation of (hetero)arenes with boron carbonitride in water

The direct reduction of inert planar arenes and heteroarenes with visible light remains rarely explored, as the energy of one visible-light photon is unable to overcome the stabilization of aromatics. Here we report a system based on boron carbonitride semiconductor, which can reduce arenes and heteroarenes in water under blue light irradiation. The system features the advantage of low-cost, high-efficiency, facile separation, benign environmental profile and broad substituent tolerance. The methodology can be extended to late-stage functionalization and/or deuteration of drugs, hormones and axially chiral compounds with conserved chirality. Moreover, gram-scale synthesis is successfully implemented with catalyst recycling. Mechanistic investigations support a consecutive blue-light-induced energy and electron transfer process, which accumulates sufficient energy to reduce arenes to arene anions by absorbing two photons successively. The metal-free system introduces a simple and sustainable reactivity mode for semiconductor photocatalysts and enriches the chemical toolkit for a class of demanding and valuable organic transformations.