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Abstract:
Thianthrenation enables direct C-H functionalization of a variety of arenes and installs synthetically useful linchpins in a highly selective fashion.[1] The obtained aryl sulfonium salts possess a higher reduction potential than aryl bromides, a class of arenes commonly employed in conventional cross-coupling catalysis.[2] Thus, metallophotoredox catalysis has emerged as a powerful method for the activation of aryl sulfonium salts generating synthetically useful aryl radicals that can engage in a broad range of transformations otherwise not readily accessible by conventional redox catalysis.[1-2]
Based on the latest findings in the Ritter group, herein, a new mode of activation of aryl sulfonium salts is reported enabling access to (het)aryl radicals by using a robust methodology without any need for photocatalysts, intense irradiation and the requirement for complex reaction setups.[3] The activation of (het)aryl sulfonium salts proceeds by homolytic C-S bond cleavage induced by α-amino radicals generated in situ from simple abundant amines in the presence of inexpensive sodium persulfate. The experimental setup is operationally simple, easily scalable as well as moisture- and oxygen-insensitive.
The obtained (het)aryl radicals engage in late-stage heteroarylations resulting in the formation of desirable (bi)heteroaryl motifs. A broad scope of (het)aryl sulfonium salts including those of biologically active compounds such as bifonazole, boscalid, famoxadone and indometacin was functionalized with five- and six-membered hetarenes including pyrazine, pyrimidine, pyridine, N-methyl pyrrole, N-methyl pyrazole and N-methyl imidazole. Furthermore, the reaction between hetaryl dibenzothiophenium salts with N-methyl pyrrole afforded valuable biheteroaryl cores, which are otherwise difficult to access.
