Single-Electron Reactivity of Thianthrene S-Oxide and Its Synthetic Application in Late-Stage Thiocyanation and Selenocyanation.

The electrophilic activation of sulfoxides allows for versatile chemical transformations usually via polar (2e-) bond-breaking and -forming. Herein, we report that activated thianthrene S-oxide (TTO) is capable of reacting with thio- and selenocyanate salts through a single-electron (1e-) pathway, driven by the particular persistence of the thianthrenium radical cation. 1,1,1,3,3,3-Hexafluoro-2-propanol (HFIP)-facilitated activation, in contrast to conventional acid activation, is crucial for selectively triggering 1e- reactivity. The activated TTO thereby enables efficient late-stage C-H thiocyanation and selenocyanation. This new strategy extends the scope to unactivated arenes as well as complex pharmaceuticals and allows for streamlined synthesis of (hybrid) p-phenylene chalcogenide oligomers. This study also reveals a direct C-H functionalization using thianthrene chemistry, yet moving beyond the well-established aryl thianthrenium intermediates.