Sulfones as Radical Progenitors:  An Unprecedented Example of Homolytic Sulfone Cleavage Facilitated by o-Stannyl Substitution of Aryl Sulfones¹

Allylic aryl sulfones bearing an o-allyldialkylstannyl moiety (1b), when converted to stannyl radical 1a, suffer homolytic cleavage via intramolecular attack of the stannyl radical on the sulfone. Allyl radicals generated in this manner can be utilized for further intramolecular radical cyclizations; thus the overall transformation can be viewed as an alkylative desulfonylation reaction. Previously unknown sulfonyl stannane polymer 5 is generated as a byproduct. The o-dibutylstannyl radical derived from nonallylic aryl sulfone 15 does not suffer homolysis but instead forms 9-membered macrocycle 19 via an intramolecular reaction with the phenylacetylene group.