A green and facile photochemical thiolate-catalyzed strategy for borylation of aryl fluorides with NHC-borane

Direct C-F bond borylation of polyfluoroarenes is a straightforward way to obtain poly-fluorinated organoboron compounds, valuable building blocks for bioactive and material molecules. However, the high BDE of C-F bonds makes the direct borylation of aromatic C-F bonds very challenging. Here, we demonstrated an efficient visible-light-induced protocol of radical-type borylation of polyfluoroarenes with a readily available aryl thiol as a catalyst and pyridine as a base. The reaction doesn't need an expensive photocatalyst and has a good substrate scope. Key mechanistic insights include: (1) boryl sulfide was formed during the reaction and affords boryl & thiyl radicals under visible light; (2) aryl thiolate worked as the single-electron reductant to generate the key delocalized anion intermediate, which then releases the fluorine anion and yields the final product. Mild conditions, no photocatalyst, broad substrate scope.