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The Vilsmeier–Haack reaction has historically been a topic of significant interest to organic chemists, and it continues to attract considerable attention. The reaction itself provides a facile route towards a large number of aromatic and heteroaromatic systems. The Vilsmeier–Haack reagent, generated from amides and halides, is found to be very important in organic synthesis. This account highlights recent developments in the synthetic utility of the Vilsmeier–Haack reagent.1 Introduction2 Formylation3 Formylation and Chlorination4 Formylation and Acetylation5 Chlorination6 ortho-Formylation7 Miscellaneous8 Conclusions

α-Aryl-α,α-difluoroketones were synthesized via decarboxylative arylation using diaryliodonium salts under catalyst-free conditions without organometallic intermediates. The products can be transformed into various difluorinated functional groups.

Trimethoxyphenyliodonium(III) acetate [TMP-iodonium(III) acetate] functions as an efficient arylation reagent for N,O-protected hydroxylamines, generating aniline derivatives in the absence of transition metal catalysts. Various N-methoxysulfonamides participated in the amination reaction to produce the corresponding N-methoxysulfonylanilines. This amination reaction was compatible with several protecting groups, including Troc (2,2,2-trichloroethoxycarbonyl), Cbz (benzyloxycarbonyl), Boc (tert-butoxycarbonyl), benzyl, acetyl, and silyl groups. This method uses TMP-iodonium(III) acetate and efficiently synthesizes various aniline derivatives that are versatile synthetic intermediates for functional organic molecules.

Hypervalent iodine (HVI) reagents have gained much attention as versatile oxidants because of their low toxicity, mild reactivity, easy handling, and availability. Despite their unique reactivity and other advantageous properties, stoichiometric HVI reagents are associated with the disadvantage of generating non-recyclable iodoarenes as waste/co-products. To overcome these drawbacks, the syntheses and utilization of various recyclable hypervalent iodine reagents have been established in recent years. This review summarizes the development of various recyclable non-polymeric, polymer-supported, ionic-liquid-supported, and metal–organic framework (MOF)-hybridized HVI reagents.1 Introduction2 Polymer-Supported Hypervalent Iodine Reagents2.1 Polymer-Supported Hypervalent Iodine(III) Reagents2.2 Polymer-Supported Hypervalent Iodine(V) Reagents3 Non-Polymeric Recyclable Hypervalent Iodine Reagents3.1 Non-Polymeric Recyclable Hypervalent Iodine(III) Reagents3.2 Recyclable Non-Polymeric Hypervalent Iodine(V) Reagents3.3 Fluorous Hypervalent Iodine Reagents4 Ionic-Liquid/Ion-Supported Hypervalent Iodine Reagents5 Metal–Organic Framework (MOF)-Hybridized Hypervalent Iodine Reagents6 Conclusion

Benzolactams have unique biological activity and high utility in the synthesis of valuable compounds with direct applicability to oxindole alkaloids and antibacterial agents. Despite recent advances in organic chemistry and the growing number of reported methods for synthesizing benzolactams, their preparation still requires a multistep process. C-H amination reactions can convert aromatic C(sp

This review summarizes double functionalization strategies for diaryliodonium(iii) salts involving the C–IIII and ortho C–H bonds, which provide short-step access to highly functionalized molecules.

The synthesis of 2-oxygenated dihydrobenzofurans involving the [3 + 2] coupling of quinone monoacetals with vinyl ethers has been realized by tetrabutylammonium triflate catalysis. The reaction involves a new activation method of the acetal moiety in quinone monoacetals under acid-free conditions affording the highly oxygenated dihydrobenzofurans. This new activation mode was achieved by using the triflate anion catalyst for stabilization of the highly reactive cationic intermediate.

Functionalized nucleobases are utilized in a wide range of fields; therefore, the development of new synthesis methods is essential for their continued application. With respect to the C6-arylation of halopurines, which possess a substituent at the N7-position, only a small number of successful cases have been reported, which is predominately a result of large steric hinderance effects. Herein, we report efficient and metal-free C6-arylations and SNAr reactions of N7-substituted chloropurines in aromatic and heteroatom nucleophiles promoted by triflimide (Tf2NH) in fluoroalcohol.

C-H/N-H bond functionalization for direct intermolecular aryl C-N couplings is a useful synthetic process. In this study, we achieved metal-free cross-dehydrogenative coupling of phenols and anilines with phenothiazines using hypervalent iodine reagents. This method affords selective amination products under mild conditions. Electron-rich phenols and anilines could be employed, affording moderate-to-high yields of

This Special Issue would cover the hot topics on recent synthetic interest in iodine reagents and related chemistry as well as the unique characteristics of hypervalent iodine compounds. The excellent reviews by the experts and eminent researchers engaged in the recent advances, i.e., preparations, reactions, and mechanistic studies of hypervalent iodine compounds, and their utilizations as reagents and organocatalysts in controlled reactions for synthesizing useful organic molecules, such as pharmaceutical compounds and organic materials, are provided in this Special Issue.

A new method for haloketo acid methyl ester synthesis on the basis of the ring-opening of cyclic α,β-unsaturated ketones followed by halogenation under mild conditions is reported. Di- and tri-haloketo acid methyl esters are conveniently synthesized via the hydrolytic ring-opening reaction through this method. Halolactones were readily obtained from these haloketo acid methyl esters by reductive cyclization employing NaBH4 and trifluoroacetic acid. Derivatizations of the obtained halolactone utilizing the exo-halomethylene moiety were also demonstrated.

We have found that the combination of Oxone® with an organoiodine compound, i.e., 2-iodobenzoic acid (2-IB), selectively yields p-quinones from monomethoxyarenes under mild conditions. In this reaction system, an organoiodine compound is immediately oxidized by Oxone® to generate cyclic hypervalent iodine (III) species in situ, which serves as the specific mediator for the selective p-quinone synthesis, preventing o-quinone formation.

A remarkable growth in hypervalent iodine-mediated oxidative transformations as stoichiometric reagents as well as catalysts have been well-documented due to their excellent properties, such as, mildness, easy handling, high selectivity, environmentally friendly nature, and high stability. This review aims at highlighting the asymmetric oxidative dearomatization reactions involving hypervalent iodine compounds. The present article summarizes asymmetric intra- and intermolecular dearomatization reactions using chiral hypervalent iodine reagents/catalysts as well as hypervalent iodine-mediated dearomatization reactions followed by desymmetrization.

An efficient protocol for C–H condensation of hypervalent iodine compounds toward arenes in fluoroalcohols has been applied to the recyclable preparation of mesityl iodonium(III) salts. The electrophilicities of [hydroxy(tosyloxy)iodo]mesitylene (MesI(OH)OTs) and iodomesitylene diacetate (MesI(OAc)2) are suitably enhanced in 2,2,2-trifluoroethanol. A series of nucleophilic aromatic compounds react smoothly with MesI(OH)OTs and MesI(OAc)2 or in situ hypervalent iodine(III) species, generated from iodomesitylene, to provide the target mesityl iodonium(III) salts in good yields at room temperature with broad functional group tolerance. This C–H condensation strategy merits high para-regioselectivities during the diaryliodonium(III) salt formation, but the major limitation in the case of low-reactive aromatic substrates is byproduct formation resulting from the self-condensation of the nucleophilic mesitylene ring in MesI(OH)OTs and MesI(OAc)2.

It was determined that diaryliodonium(III) triflates bearing a trimethoxybenzene (TMP) auxiliary are more reactive than the reported selective aryl-transfer iodonium salts in the N-arylation of benzimidazoles and other types of azole compounds under catalytic conditions. The TMP-iodonium(III) salts can thus effectively facilitate the reaction at 50 °C or below, producing the corresponding N-arylated biaryls without the formation of TMP-derived coupling byproducts. Utilization of this TMP reagent under mild conditions would prevent the underlying problem of participation of the auxiliary group in the coupling reactions, which is observed while using the iodonium(III) salts that require elevated temperatures.

Oxidative coupling strategies that can directly convert the C–H group for chemical transformations are, in theory, ideal synthetic methods to reduce the number of synthetic steps and byproduct generation. Hypervalent iodine reagents have now become one of the most promising tools in developing oxidative couplings due to their unique reactivities that are replacing metal oxidants. As part of our continuous development of oxidative coupling reactions, we describe in this report highly efficient μ-oxo hypervalent iodine catalysts for the direct oxidative coupling of N-methoxyamides and related compounds with aromatic hydrocarbons. The excellent TONs, up to over 100 times, with a best catalyst loading of 0.5 mol% were determined for the oxidative C–H/N–H coupling method, which can provide the most straightforward route to obtaining these unique arylamide compounds.

Functionalized nucleobases are utilized in a wide range of fields; therefore, the development of new synthesis methods is essential for their continued application. With respect to the C

We report a convenient and practical method for the preparation of nonexplosive cyclic hypervalent iodine(III) oxidants as efficient organocatalysts and reagents for various reactions using Oxone® in aqueous solution under mild conditions at room temperature. The thus obtained 2-iodosobenzoic acids (IBAs) could be used as precursors of other cyclic organoiodine(III) derivatives by the solvolytic derivatization of the hydroxy group under mild conditions of 80 °C or lower temperature. These sequential procedures are highly reliable to selectively afford cyclic hypervalent iodine compounds in excellent yields without contamination by hazardous pentavalent iodine(III) compound.

Nucleophilic aromatic substitution (SNAr) reactions can provide metal-free access to synthesize monosubstituted aromatic compounds. We developed efficient SNAr conditions for p-selective substitution of polyfluoroarenes with phenothiazine in the presence of a mild base to afford the corresponding 10-phenylphenothiazine (PTH) derivatives. The resulting polyfluoroarene-bearing PTH derivatives were subjected to a second SNAr reaction to generate highly functionalized PTH derivatives with potential applicability as photocatalysts for the reduction of carbon–halogen bonds.

In organic synthesis, due to their high electrophilicity and leaving group properties, halogens play pivotal roles in the activation and structural derivations of organic compounds. Recently, cyclizations induced by halogen groups that allow the production of diverse targets and the structural reorganization of organic molecules have attracted significant attention from synthetic chemists. Electrophilic halogen atoms activate unsaturated and saturated hydrocarbon moieties by generating halonium intermediates, followed by the attack of carbon-containing, nitrogen-containing, oxygen-containing, and sulfur-containing nucleophiles to give highly functionalized carbocycles and heterocycles. New transformations of halogenated organic molecules that can control the formation and stereoselectivity of the products, according to the difference in the size and number of halogen atoms, have recently been discovered. These unique cyclizations may possibly be used as efficient synthetic strategies with future advances. In this review, innovative reactions controlled by halogen groups are discussed as a new concept in the field of organic synthesis.

An oxidation system comprising phenyliodine(III) diacetate (PIDA) and iodosobenzene with inorganic bromide, i.e., sodium bromide, in an organic solvent led to the direct introduction of carboxylic acids into benzylic C–H bonds under mild conditions. The unique radical species, generated by the homolytic cleavage of the labile I(III)–Br bond of the in situ-formed bromo-λ3-iodane, initiated benzylic carboxylation with a high degree of selectivity for the secondary benzylic position.