Borylation of Aryl Halides Induced by Visible Light Under Open-To-Air Environment

Aryl boronate esters play a key role in organic chemistry, making them suitable reagents for subsequent derivatizations, such as preparation of bioactive molecules. The search for novel and sustainable procedures for their synthesis still endeavors the organic community. In this investigation, we developed a new methodology to obtain aryl boronate esters that involved the employment of visible light as energy source, the absence of photocatalyst, and the utilization of purely organic confined media, allowing the reaction to proceed under an open-to-air environment. The gel network provided an adequate stabilizing microenvironment to support wide substrate scope for the borylation of commercially available aryl halides containing different functional groups, such as carbonyl, alcohol, esters, amines, and trifluoromethyl, giving in some cases quantitative product yields. Mechanistic evidence from both absorptivity measurements and NMR experiments revealed not only the formation of a ground-state complex but also the nature of this complex via hydrogen bonding. These findings were further explained by DFT calculations to assess the complex formation and the specific photoreactivity induced.