Mechanistic insight into thermal 1,3- and 1,5-sulfonyl migrations of N-arenesulfonylphenothiazines and N-arenesulfonylphenoxazines

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The substrate scope and mechanistic insight of the thermal-induced 1,3- and 1,5-sulfonyl migration reactions of various sulfonamides have been investigated. The results indicate that both N-arenesulfonylphenothiazines and N-arenesulfonylphenoxazines can undergo 1,3- and 1,5-sulfonyl migrations to afford the corresponding aryl sulfone derivatives in modest regioselectivities and yields under thermal and neutral conditions. The homolytic cleavage of the sulfonamide bond and intermolecular radical–radical coupling reaction mechanism was proposed for the 1,3- and 1,5-sulfonyl migrations on the basis of intercrossing and competitive capture experiments.