Photoinduced metal-free borylation of aryl halides catalysed by an in situ formed donor-acceptor complex

Organoboron compounds are very important building blocks which can be applied in medicinal, biological and industrial fields. However, direct borylation in a metal free manner has been very rarely reported. Herein, we described the successful direct borylation of haloarenes under mild, operationally simple, catalyst-free conditions, promoted by irradiation with visible light. Mechanistic experiments and computational investigations indicate the formation of an excited donor-acceptor complex with a -3.12 V reduction potential, which is a highly active reductant and can facilitate single-electron-transfer (SET) with aryl halides to produce aryl radical intermediates. A two-step one-pot method was developed for site selective aromatic C-H bond borylation. The protocol's good functional group tolerance enables the functionalization of a variety of biologically relevant compounds, representing a new application of aryl radicals merged with photochemistry.

Automated summary

Organoboron compounds are valuable in medicinal, biological, and industrial fields. This study achieved direct borylation of haloarenes without the use of metal catalysts by irradiating with visible light. Mechanistic experiments and computational investigations revealed the formation of an excited donor-acceptor complex with a high reduction potential, enabling single-electron-transfer reactions with aryl halides.