The preparation, structure, and chemistry of hypervalent iodine compounds are reviewed with emphasis on their synthetic application. Compounds of iodine possess reactivity similar to that of transition metals, but have the advantage of environmental sustainability and efficient utilization of natural resources. These compounds are widely used in organic synthesis as selective oxidants and environmentally friendly reagents. Synthetic uses of hypervalent iodine reagents in halogenation reactions, various oxidations, rearrangements, aminations, C−C bond-forming reactions, and transition metal-catalyzed reactions are summarized and discussed. Recent discovery of hypervalent catalytic systems and recyclable reagents, and the development of new enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important achievement in the field of hypervalent iodine chemistry. One of the goals of this Review is to attract the attention of the scientific community as to the benefits of using hypervalent iodine compounds as an environmentally sustainable alternative to heavy metals.

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Azidoiodinanes 2 and 4a,b can be prepared from the appropriate benziodoxoles 1 and 3a,b and trimethylsilyl azide in the form of stable, crystalline compounds. A single-crystal X-ray analysis for azide 4b revealed the expected hypervalent iodine distorted T-shaped geometry with the N1−I−O bond angle of 169.5 (2) degrees. The lengths of the bonds to the iodine atom, I−N (2.18 Å), I−O (2.13 Å), and I−C (2.11 Å), are within the range of typical single covalent bonds in organic derivatives of polyvalent iodine, while the previously reported benziodoxoles generally have an elongated I−O bond. The geometry of the I(III)NNN fragment in 4b is similar to the literature electron diffraction data on monomeric iodine azide, IN3, in gas phase. Azidobenziodoxoles 2,4 are potentially useful reagents for direct azidation of organic substrates, such as dimethylanilines, alkanes, and alkenes. Reaction of 2 with dimethylanilines proceeds under mild conditions to afford the respective N-azidomethyl-N-methylanilines in excellent yield. Alkanes, cycloalkanes, and adamantanes react with azidobenziodoxoles 2 or 4b in the presence of radical initiators at 80−132 °C with the formation of tertiary alkylazides, while reaction of norbornane leads to exo-2-azidonorbornane. Under similar conditions cyclohexene is selectively azidated at the allylic position.

Organohypervalent iodine reagents have attracted significant recent interest as versatile and environmentally benign oxidants with numerous applications in organic synthesis. This Perspective summarizes synthetic applications of hypervalent iodine(V) reagents: 2-iodoxybenzoic acid (IBX), Dess-Martin periodinane (DMP), pseudocyclic iodylarenes, and their recyclable polymer-supported analogues. Recent advances in the development of new catalytic systems based on the generation of hypervalent iodine species in situ are also overviewed.

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