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.