Free Radical Self-Immolative 1,2-Elimination and Reductive Desulfonylation of Aryl Sulfones Promoted by Intramolecular Reactions with Ortho-Attached Carbon-Centered Radicals¹

Aryl sulfones bearing an o-(bromomethyl)dimethylsilyl moiety (1), when heated with AIBN and tributyltin hydride, suffer radical elimination under mild conditions to give olefins and stannyl sulfinate 7 in high yield. The mechanism is shown to proceed via intramolecular beta-sulfonyl hydrogen abstraction by o-silylmethylene radical 2. This step also shows a large deuterium isotope effect of 12:1. In contrast, radical intermediate 24, generated by tris(trimethylsilyl)silane radical addition to o-allylsilane 23, undergoes intramolecular attack on the sulfone, resulting in homolytic sulfone cleavage to afford reduced products and cyclic sulfone byproduct 25.