A proof‐of‐concept study of hypervalent chalcogenonium⋅⋅⋅π bonding catalysis was performed. A new catalytic strategy using 1,2‐oxaselenolium salts as chalcogen bond donors and alkenes as chalcogen bond acceptors is described. The feasibility of this concept is demonstrated by the use of trisubstituted selenonium salts in the metal‐free catalytic hydrofunctionalization and polymerization of alkenes via unconventional seleniranium ion‐like intermediates. The results indicate that counter anions have a significant effect on the catalysis based on hypervalent chalcogenonium⋅⋅⋅π bonding interactions.

γ-Butenolides are useful structural motifs in many pharmaceutically relevant compounds. In particular, halogenated γ-butenolides are attractive building blocks because the halogen handles can readily be manipulated to give various functional molecules. In this study, a catalytic synthesis of halogenated γ-butenolides from cyclopropene carboxylic acids was developed using zwitterionic catalysts and N-haloamides as the halogen sources. The catalytic protocol could also be applied to the synthesis of halogenated pyrrolones by using cyclopropene amides as the starting materials.

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.