Study and Applications of Tetrasubstituted Hypervalent Selenium-Halogen Species in Catalytic Electrophilic Halogenations

Abstract

Electrophilic halogenation reactions are highly useful in various areas. N-Haloamides are commonly used as halogen sources because of high stability and commercial availability. In order to activate N-haloamides, Lewis basic chalcogens are commonly used as catalysts to site-isolate the strongly coordinating amide moieties. However, the corresponding trisubstituted chalcogenonium-halogen cationic intermediate is sensitive to moisture and nucleophiles, leading to poor compatibility in some reactions. Herein, we report an efficient catalytic halogenation protocol using phenyl selenium with ortho-substituted carboxylic acid as the catalyst. Mechanistic study suggests that a tetrasubstituted neutral hypervalent Se-halogen species is responsible for the high reactivity. This active intermediate was found to be moisture-stable, and the catalytic system is applicable to a wide range of electrophilic functionalization reactions including haloamidation, intermolecular haloesterification, halocycloetherification, halolactonization, aromatic halogenation, halopolyene cyclization, and selenylation reactions.