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Hypervalent iodine(III) compounds have found wide application in modern organic chemistry as environmentally friendly reagents and catalysts. Hypervalent iodine reagents are commonly used in synthetically important halogenations, oxidations, aminations, heterocyclizations, and various oxidative functionalizations of organic substrates. Iodonium salts are important arylating reagents, while iodonium ylides and imides are excellent carbene and nitrene precursors. Various derivatives of benziodoxoles, such as azidobenziodoxoles, trifluoromethylbenziodoxoles, alkynylbenziodoxoles, and alkenylbenziodoxoles have found wide application as group transfer reagents in the presence of transition metal catalysts, under metal-free conditions, or using photocatalysts under photoirradiation conditions. Development of hypervalent iodine catalytic systems and discovery of highly enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important recent achievement in the field of hypervalent iodine chemistry. Chemical transformations promoted by hypervalent iodine in many cases are unique and cannot be performed by using any other common, non-iodine-based reagent. This review covers literature published mainly in the last 7-8 years, between 2016 and 2024.

This review summarizes the structural and synthetic aspects of heterocyclic molecules incorporating an atom of a hypervalent main-group element. The term "hypervalent" has been suggested for derivatives of main-group elements with more than eight valence electrons, and the concept of hypervalency is commonly used despite some criticism from theoretical chemists. The significantly higher thermal stability of hypervalent heterocycles compared to their acyclic analogs adds special features to their chemistry, particularly for bromine and iodine. Heterocyclic compounds of elements with double bonds are not categorized as hypervalent molecules owing to the zwitterionic nature of these bonds, resulting in the conventional 8-electron species. This review is focused on hypervalent heterocyclic derivatives of nonmetal main-group elements, such as boron, silicon, nitrogen, carbon, phosphorus, sulfur, selenium, bromine, chlorine, iodine(III) and iodine(V).

Pseudocyclic arylbenziodoxaboroles are unique aryne precursors under neutral aqueous conditions that selectively react with organic sulfides, forming the corresponding sulfonium salts. This reaction is compatible with various substituents (alkyl, halogen, CN, NO 2 , CHO, and cyclopropyl) in the aromatic ring or alkyl group of the sulfide. Similar reactions of sulfoxides afford o -hydroxy-substituted sulfonium salts. The structures of key products were confirmed by X-ray analysis.

We report a greener peptide coupling using bicyclic benziodazolone and triarylphosphine as coupling reagents. Bicyclic benziodazolone also works as a base and can be recovered as the corresponding iodine(I) compound after use, which can be converted to the original iodine(III) reagent by electrolytic oxidation.

Various five-membered cyclic dibenzobromolium salts (dibenzo[ b , d ]bromol-5-ium chloride, nitrate, hydrogen sulfate, dihydrogen phosphate, trifluoroacetate, and tetrafluoroborate) were prepared by diazotization-cyclization of 2'-bromo-[1,1'-biphenyl]-2-amine in solution of appropriate acids. The chlorolium analogues (iodide, trifluoroacetate, and tetrafluoroborate) were obtained by a similar procedure. Additional dibenzohalolium derivatives (dibenzo[ b , d ]bromol-5-ium and dibenzo[ b , d ]chlorol-5-ium azides, bis(trifluoromethanesulfonyl)imidates, thiocyanates, and trifluoromethanesulfonates) were prepared by anion exchange. Structures of ten of these dibenzohalolium derivatives were established by X-ray analysis. Bond distances and angles for the halogen atoms in different dibenzohalolium derivatives were summarized and discussed., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)