S-Oxide peri-Annulated Blatter Radicals: A Paradigm for Chiral Radicals

Selective oxidation of the sulfur atom in two S-peri-annulated Blatter radicals with Oxone gives racemic sulfoxides, one of which was resolved into enantiomers and characterized by electronic circular dichroism (ECD). They are the first examples of a potentially broad class of centrally chiral radicals, in which the endocyclic chirality center in the π polycyclic radical skeleton represents a new paradigm in the structural chemistry of radicals. A higher ratio of Oxone gives analogous endocyclic sulfones. The resulting stable radicals were characterized by spectroscopic (UV-vis, ECD, EPR), electrochemical, XRD, and DFT methods.