Radical Reactivity of Aryl Thianthrenium Salts

Abstract

Functionalization of the C(sp2)–H bond is a challenging yet highly useful synthetic task due to its relative inertness and commonality among functional groups. Arene thianthrenation is an emerging C(sp2)–H bond activation strategy featuring high chemo- and regioselectivity in the modification of structurally diverse substrates. The resultant aryl thianthrenium (Ar–TT⁺) salts exhibit divergent single- and two-electron reactivity modes, which have enabled new C(sp2)–bond formation to the main group elements through mechanistically distinct routes. This review complements the existing literature on the two-electron behavior of Ar–TT⁺ salts by highlighting the enhanced control of radical reactivity achieved in the site-selective thianthrenation of arenes and subsequent C(sp2)–S bond homolysis to generate aryl radicals. Discussion of the structural and electronic properties of Ar–TT⁺ salts promoting single-electron reactivity under mild conditions, functional group tolerance, enhanced platform cross-compatibility, and increased potential for sustainability through catalysis is a thematic focus throughout. Identification of these prior methodological advancements culminates in a prospectus on the opportunities for future reaction development.