Catalyst-Free C(sp2)-H Borylation through Aryl Radical Generation from Thiophenium Salts via Electron Donor-Acceptor Complex Formation.

Abstract

Aryl borates lie at the heart of carbon-carbon bond couplings, and they are widely applied to the synthesis of functional materials, pharmaceutical compounds, and natural products. Currently, synthetic methods for aryl borates are mostly limited to metal-catalyzed routes, and nonmetallic strategies remain comparatively underdeveloped. Herein, we report a mild, scalable, visible-light-induced cross-coupling between aryl dibenzothiophenium triflate salts and bis(catecholato)-diboron for the construction of C-B bonds in the absence of base, transition metal-ligand complex, or photoredox catalyst. Mechanistic studies reveal that this transformation is achieved through an electron donor-acceptor (EDA) complex activation in the absence of a catalyst. The mild reaction conditions allow the preparation of aromatic borates in good yields with excellent functional group tolerance. This photochemical protocol was also successfully applied to the late-stage modification of natural products and the synthesis of a drug intermediate, greatly demonstrating broadened utility.