Photocatalytic Direct Borylation of Benzothiazole Heterocycles via a Triplet Activation Strategy.

Boron compounds are widely employed in organic chemistry, pharmaceuticals, and materials science. Among them, borylated heterocycles serve as versatile synthons for the construction of new C-C or C-heteroatom bonds via coupling or radical processes. Such methods for direct C-H borylation reactions are of high synthetic value to reduce the number of synthetic steps and the amount of waste and to improve efficiency. Despite significant advances, the borylation of heterocycles remains an ongoing challenge with great potential for applications in chemical synthesis. Herein, we describe a photocatalytic C-H borylation reaction of five-membered ring heterocycles by employing a stable N-heterocyclic carbene borane as the borylating reagent and a photoredox catalyst. Under green and mild conditions, C-H borylation was achieved on a series of benzo-fused five-membered heterocyclic compounds. Further studies demonstrate the utility of this approach for applications in pharmaceutical and agrochemical research.