Photoinduced Borylation of Aryl Halides, Including Aryl Chlorides, Under Photocatalyst‐Free Conditions

ABSTRACT

A photocatalyst‐free photoinduced borylation of activated aryl chlorides has been developed using a simple base/additive system. Under 365 nm LED irradiation, electron‐deficient aryl chlorides underwent borylation with bis(pinacolato)diboron in MeCN in the presence of aqueous TBAOH and CsF, affording arylboronates under transition‐metal‐free conditions. Optimization revealed that both base and fluoride additive are essential, with TBAOH/CsF effectively promoting activation of electron‐deficient aryl chlorides. The method tolerated activated aryl chlorides bearing electron‐withdrawing substituents, including cyano and amide groups, whereas electron‐neutral and electron‐rich substrates showed markedly lower reactivity. Aryl bromides and iodides also participated under related conditions, indicating strong dependence on the halogen substituent. Control experiments confirmed that light irradiation is required and that the reaction is not thermally initiated. Radical‐quenching and deuterium‐labeling experiments support aryl radical intermediates. Accordingly, a mechanism involving photoinduced single‐electron transfer to the aryl halide followed by C─X bond cleavage is proposed.