α‑C(sp<sup>3</sup>)–H (Hetero)Arylation\nof Thioethers Enabled by Photoexcited Triplet Ketone Catalysis

We report herein α-C(sp<sup>3</sup>)–H (hetero)arylation\nof thioethers enabled by dual nickel and photoexcited triplet ketone\ncatalysis. The mild reaction conditions of this protocol tolerate\na variety of functional groups and further facilitate the late-stage\nfunctionalization of biologically relevant molecules to afford corresponding\nproducts in moderate to good yields. Preliminary mechanistic studies\nsuggest that the generation of the α-thioalkyl radical takes\nplace through a hydrogen atom transfer (HAT) event, which is involved\nin the rate-limiting step and in the nickel cycle, the reaction of\nthe α-thioalkyl radical with Ni(0)L<sub><i>n</i></sub> catalyst followed by oxidative addition of aryl bromide is the dominating\npathway. Furthermore, the heteroaromatic benzylic thioethers can also\nbe achieved from the corresponding reduced 4-cyano pyridine derivatives\nin the presence of a ketone catalyst through a radical–radical\ncoupling reaction without metal. The increased yield of the products\nin the presence of DABCO might indicate a higher rate of α-thioalkyl\nradical formation from thioethers through the HAT event by DABCO radical\ncation.