Copper-Catalyzed Chemoselective O-Arylation of Oxindoles: Access to Cyclic Aryl Carboxyimidates

We have developed a highly efficient base- and additive-free chemoselective CuO-catalyzed strategy for the O-arylation of 2-oxindoles to synthesize 2-phenoxy-3H-indole and 2-phenoxy-1H-indole derivatives in the presence of diaryl iodonium salts. This method offers a variety of O-arylated oxindoles in good to excellent yields under relatively milder reaction conditions. Furthermore, this methodology was extended for the O-arylation of 2-pyridinone and isoindoline-1-one derivatives as well.

Diaryliodonium Salts Enabled Arylation, Arylocyclization, and Aryl-Migration

Our research interest focusing on synthetic methodology with diaryliodonium salts, is summarized in this account. Besides employing a dual activation strategy of C-I and ortho C-H bonds, we have introduced vicinal functional groups at ortho-positions of diaryliodonium salts, in which their unique reactivities have been explored in various processes, including arylation, diarylation, cascade annulation, benzocyclization, arylocyclization, and intramolecular aryl migration. The variety of mechanisms of these reactions that involves either transition metals, especially palladium in organometallic catalysis, or transition-metal free conditions, were discussed in the context.

Diaryliodonium(III) Salts in One-Pot Double Functionalization of C–IIII and ortho C–H Bonds

Since the 1950s, diaryliodonium(III) salts have been demonstrated to participate in various arylation reactions, forming aryl–heteroatom and aryl–carbon bonds. Incorporating the arylation step into sequential transformations would provide access to...

Diaryliodonium Salt-Based Synthesis of N-Alkoxyindolines and Further Insights into the Ishikawa Indole Synthesis

A diaryliodonium salt-based strategy enabled the first systematic synthesis of rarely accessible N-alkoxyindolines. Mechanistic analyses suggested that the reaction likely involves reductive elimination of iodobenzene from iodaoxazepine via a four-membered transition state, followed by Meisenheimer rearrangement. Substrates with N-carbamate protection afforded indole in a manner similar to that of the Ishikawa indole synthesis. Preinstallation of a stannyl group as an iodonium salt precursor greatly expanded the substrate scope, and further mechanistic insights are discussed.

O-Cyclopropyl hydroxylamines: gram-scale synthesis and utility as precursors for N-heterocycles

O-Cyclopropyl hydroxylamines, now accessible via a novel and scalable synthetic route, have been demonstrated to be bench-stable and practical precursors for the synthesis of N-heterocycles via a di-heteroatom [3,3]-sigmatropic rearrangement. In order to study the reactivity of these compounds in depth, a robust synthesis of both ring-substituted and ring-unsubstituted O-cyclopropyl hydroxylamines has been developed. Metal-free conditions for the facile N-arylation of these precursors were also identified. It was found that the N-arylated O-cyclopropyl hydroxamates can efficiently undergo a one-pot [3,3]-sigmatropic rearrangement/cyclization/rearomatization cascade under base-mediated conditions to furnish a structurally diverse set of substituted tetrahydroquinolines.

Efficient solvent- and temperature-tuned access to aldoxime ethers and phenolic functions by Pd-catalyzed C–O cross-coupling of aldoximes with aryl bromides and bromo-chalcones

A single method with a functionality switching option, to access oxime ethers and phenols, was developed for the first time for the Pd-catalyzed C–O cross-coupling of aryl bromides and bromo-chalcones with aldoximes.

Generation and Rearrangement of N,O-Dialkenylhydroxylamines for the Synthesis of 2-Aminotetrahydrofurans

A new diastereoselective route to 2-aminotetrahydrofurans has been developed from N,O-dialkenylhydroxylamines. These intermediates undergo a spontaneous C-C bond-forming [3,3]-sigmatropic rearrangement followed by a C-O bond-forming cyclization. A copper-catalyzed N-alkenylation of an N-Boc-hydroxylamine with alkenyl iodides, and a base-promoted addition of the resulting N-hydroxyenamines to an electron-deficient allene, provide modular access to these novel rearrangement precursors. The scope of this de novo synthesis of simple nucleoside analogues has been explored to reveal trends in diastereoselectivity and reactivity. In addition, a base-promoted ring-opening and Mannich reaction has been discovered to covert 2-aminotetrahydrofurans to cyclopentyl β-aminoacid derivatives or cyclopentenones.

Metal-Involving Synthesis and Reactions of Oximes

This review classifies and summarizes the past 10-15 years of advancements in the field of metal-involving (i.e., metal-mediated and metal-catalyzed) reactions of oximes. These reactions are diverse in nature and have been employed for syntheses of oxime-based metal complexes and cage-compounds, oxime functionalizations, and the preparation of new classes of organic species, in particular, a wide variety of heterocyclic systems spanning small 3-membered ring systems to macroheterocycles. This consideration gives a general outlook of reaction routes, mechanisms, and driving forces and underlines the potential of metal-involving conversions of oxime species for application in various fields of chemistry and draws attention to the emerging putative targets.

Aryl Transfer Selectivity in Metal-Free Reactions of Unsymmetrical Diaryliodonium Salts

Aromatic rings are found in a wide variety of products, including pharmaceuticals, agrochemicals, and functional materials. Diaryliodonium salts are new reagents used to transfer aryl groups under both metal-free and metal-catalyzed reactions and thereby synthesize arene-containing compounds. This minireview focuses on recent studies in selective aryl transfer reactions from unsymmetrical diaryliodonium salts under metal-free conditions. Reactions reported from 2007 to 2017, which represents a period of significant growth in diaryliodonium salt chemistry, are presented and organized by the type of reactive intermediate formed in the reaction. Specifically, reactions involving λ³ -iodane, λ³ -iodane radical anions, aryl radicals, and arynes are discussed. Chemoselectivity trends in aryl transfer are compared and contrasted across reaction intermediates and translation to potential auxiliaries are posited.

Metal-free Synthesis of Aryl Amines: Beyond Nucleophilic Aromatic Substitution

A mild and metal-free approach to C-N coupling is described that employs diaryliodonium salt electrophiles and secondary aliphatic amine nucleophiles. This reaction results in direct ipso-substitution of the iodonium moiety and unsymmetrical aryl(TMP)iodonium salts are primarily employed. Moreover, arene substituents and substitution patterns that currently pose a challenge to classical metal-free methods are accommodated and the alicyclic amine nucleophiles used here are unprecedented in other contemporary metal-free C-N coupling reactions.

Advances in Synthetic Applications of Hypervalent Iodine Compounds

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.

Review of the synthesis of acyclic and cyclic oxime ethers

Oxime ethers have attracted much attention due to their potential biological activities and wide variety of synthetic applications.

A Mild and General One-Pot Synthesis of Densely Functionalized Diaryliodonium Salts

Diaryliodonium salts are powerful and widely used arylating agents in organic chemistry. Here we report a scalable, synthesis of densely functionalized diaryliodonium salts from aryl iodides under mild conditions. This two-step, one-pot process has remarkable functional group tolerance, is compatible with commonly employed acid-labile protective group strategies, avoids heavy metal and transition metal reagents, and provides a direct route to stable precursors to PET imaging agents.

Base promoted direct C4-arylation of 4-substituted-pyrazolin-5-ones with diaryliodonium salts

A metal-free approach for the C4-arylation of 4-substituted-pyrazolin-5-ones with diaryliodonium salts was developed.

Metal-free one-pot sequential direct diarylation of pyrazolin-5-ones with diaryliodonium salts

A novel and efficient one-pot sequential C4-diarylation of pyrazolin-5-ones with diaryliodonium salts at room temperature in the absence of a metal catalyst was reported.