Site-selective and versatile aromatic C−H functionalization by thianthrenation

Direct C–H functionalization can quickly increase useful structural and functional molecular complexity1–3. Site selectivity can sometimes be achieved through appropriate directing groups or substitution patterns1–4—in the absence of such functionality, most aromatic C–H functionalization reactions provide more than one product isomer for most substrates1,4,5. Development of a C–H functionalization reaction that proceeds with high positional selectivity and installs a functional group that can serve as a synthetic linchpin for further functionalization would provide access to a large variety of well-defined arene derivatives. Here we report a highly selective aromatic C–H functionalization reaction that does not require a particular directing group or substitution pattern to achieve selectivity, and provides functionalized arenes that can participate in various transformations. We introduce a persistent sulfur-based radical to functionalize complex arenes with high selectivity and obtain thianthrenium salts that are ready to engage in different transformations, via both transition-metal and photoredox catalysis. This transformation differs fundamentally from all previous aromatic C–H functionalization reactions in that it provides direct access to a large number of derivatives of complex small molecules, quickly generating functional diversity with selectivity that is not achievable by other methods.