Photoinduced Metal‐Free C–H Borylation via Thianthrenium Electron Donor–Acceptor Complexes

Herein, we report a photoinduced, metal- and photocatalyst-free protocol for site-selective C-H borylation via aryl thianthrenium (TT) salts, addressing key limitations of prior electron donor-acceptor (EDA)-based strategies. This approach leverages in situ-formed [Et₃N·B₂pin₂] adducts with TT salts to generate a photoactive EDA complex, circumventing the need for exogenous electron donors and activating reagents while enabling exceptional tolerance of sensitive groups (cyano, aldehyde, amide) and complex natural products, with yields up to 95%. Its synthetic utility was validated by late-stage modification of bioactive molecules, and mechanistic studies confirmed the unique role of the EDA complex in driving the transformation without additional additives. This strategy represents a paradigm shift in metal-free borylation, combining operational simplicity with an expanded substrate scope and superior functional group compatibility.