Hypervalent Iodine Chemistry

Recently, hypervalent iodine reagents have been extensively used in organic synthesis. A variety of reactions available for natural product syntheses have been developed using phenyliodine(III) diacetate (PIDA), phenyliodine(III) bis(trifluoroacetate) (PIFA), and other iodine(III) and (V) reagents. These reactions are expected to have applications in pharmaceutical and agrochemical processes because of their safety, mild reaction conditions, and high yields of pure products. Under such considerations, this chapter focuses on the oxidative coupling reactions of hypervalent iodine reagents found in total syntheses of biologically active natural products and their related compounds.

This chapter highlights recent developments in phenol dearomatization using organoiodane reagents and a selection of applications in natural product synthesis.

Hypervalent iodine(III) reagents have been widely exploited in a diverse array of synthetic transformations. This chapter focuses on the general application of hypervalent iodine(III) reagents in the de novo synthesis and in the late stage functionalization of heterocyclic compounds.

Recent progress in the area of hypervalent iodine-mediated and catalyzed amination reaction of hydrocarbons is reviewed. These reactions comprise processes under both intra and intermolecular control and include the functionalization of aromatic C–H bonds as well as conversion of sp-, sp²-, and sp³-hybridized carbon atoms. These developments demonstrate that hypervalent iodine(III) methodology has reached a high level in amination chemistry. The individual reactions are discussed with a focus on mechanistic details and emphasis is made to the underlying hypervalent iodine reagents, for which structural information is available.

This chapter focuses on recent developments in metal-free and metal-catalyzed arylations with diaryliodonium salts (diaryl-λ³-iodanes). Synthetic routes to diaryliodonium salts are briefly described, and chemoselectivity trends with unsymmetric iodonium salts are discussed.

This chapter describes synthesis, structural properties, activation modes, and applications of hypervalent iodine reagents for trifluoromethylation, thereby focusing on recent advances.

Alkynes are among the most versatile functional groups in organic synthesis. They are also frequently used in chemical biology and materials science. Whereas alkynes are traditionally added as nucleophiles into organic molecules, hypervalent iodine reagents offer a unique opportunity for the development of electrophilic alkyne synthons. Since 1985, alkynyliodonium salts have been intensively used for the alkynylation of nucleophiles, in particular soft carbon nucleophiles and heteroatoms. They have made an especially strong impact in the synthesis of highly useful ynamides. Nevertheless, their use has been limited by their instability. Since 2009, more stable ethynylbenziodoxol(on)e (EBX) reagents have been identified as superior electrophilic alkyne synthons in many transformations. They can be used for the alkynylation of acidic C–H bonds with bases or aromatic C–H bonds using transition metal catalysts. They were also highly successful for the functionalization of radicals or transition metal-catalyzed domino processes. Finally, they allowed the alkynylation of a further range of heteroatom nucleophiles, especially thiols, under exceptionally mild conditions. With these recent developments, hypervalent iodine reagents have definitively demonstrated their utility for the efficient synthesis of alkynes based on non-classical disconnections.

This chapter describes recent developments in stereoselective synthesis using hypervalent iodine reagents.

This chapter overviews the roles of transition metal complexes having the organoiodine(III) reagents iodosylarenes (ArIO) and (imino)iodoarenes (ArINR) as ligands in catalysis. Mechanistic implications are discussed.

Halogen bonds occur when electrophilic halogens (Lewis acids) attractively interact with donors of electron density (Lewis bases). This term is commonly used for interactions undertaken by monovalent halogen derivatives. The aim of this chapter is to show that the geometric features of the bonding pattern around iodine in its hypervalent derivatives justify the understanding of some of the longer bonds as halogen bonds. We suggest that interactions directionality in ionic and neutral λ³-iodane derivatives is evidence that the electron density distribution around iodine atoms is anisotropic, a region of most positive electrostatic potential exists on the extensions of the covalent bonds formed by iodine, and these positive caps affect, or even determine, the crystal packing of these derivatives. For instance, the short cation–anion contacts in ionic λ³-iodane and λ⁵-iodane derivatives fully match the halogen bond definition and geometrical prerequisites. The same holds for the short contacts the cation of ionic λ³-iodanes forms with lone-pair donors or the short contacts given by neutral λ³-iodanes with incoming nucleophiles. The longer and weaker bonds formed by iodine in hypervalent compounds are usually called secondary bondings and we propose that the term halogen bond can also be used. Compared to the term secondary bond, halogen bond may possibly be more descriptive of some bonding features, e.g., its directionality and the relationships between structure of interacting groups and interaction strength.