Sulfur dioxide hydroxy radical reaction

Motherwell s group developed an original approach to the synthesis of biaryls based on the intramolecular free-radical zjo o-substitution reaction. This includes the reaction of ortho-io o (or bromo) phenols, A -methylanilines or 7V-methylbenzamides with various arylsulfonyl chlorides to give the respective sulfonates XXX, Ai-methyl sulfonamides XXXI, or Y-acylsulfonamides XXXII. The latter are reacted with tri- -butyltin hydride in the presence of azobisisobutyronitrile (AIBN) in refluxing benzene to produce spirocyclic intermediate XXXIII, which, upon extrusion of sulfur dioxide, afforded the ort/jo-hydroxy- XXXIV, methyamino- XXXV, or iV-methyl carboxamido-substituted biphenyls XXXVI in moderate to good yields [1-4], Scheme 1. 

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