Transition-Metal-Free Difunctionalization of Sulfur Nucleophiles

Metal-Free Synthesis of Benzisoxazolones Utilizing ortho-Ester and ortho-Cyano-Functionalized Diaryliodonium Salts with Protected Hydroxylamines

Herein, we report the development of metal-free one/two-pot procedures for the synthesis of benzo[c]isoxazol-3(1H)-one (benzisoxazolone) heterocycles by designing diaryliodonium salts featuring ortho-ester or nitrile functional groups. These react smoothly with protected hydroxylamines under mild conditions to produce N-arylhydroxylamine intermediates, which readily cyclize to give benzisoxazolone derivatives under acidic conditions. This metal-free process maintains the weak N-O bond, tolerates a wide range of diaryliodonium salts and protected hydroxylamines with diverse functional/protecting groups, thereby overcoming the challenges associated with previous transformations. The protocol expands the reaction scope and broadens the chemical space of the fused isoxazolone backbones to include unprecedented five-membered heteroaryl-fused isoxazolones in high yields. This method is also applicable to gram-scale synthesis, and the resulting benzisoxazolones can be effectively derivatized at the N-position to afford valuable compounds.

Synthesis of Diaryl Ethers via Hypervalent Iodine-Mediated C-H Functionalization

A hypervalent iodine-reagent-based C-H functionalization strategy was utilized to synthesize diaryl ethers. This method directly transforms various arenes into their corresponding diaryliodonium salts, followed by a C-O coupling reaction to produce structurally diverse diaryl ethers. The efficacy of this approach in the late-stage structural modifications of complex molecules was demonstrated.

Transition-Metal-Free C-Diarylations to Reach All-Carbon Quaternary Centers

Herein, we disclose a convenient protocol for the α-diarylation of carbon nucleophiles to yield heavily functionalized quaternary products. Diaryliodonium salts are utilized to transfer both aryl groups under transition-metal-free conditions, which enables an atom-efficient and high-yielding method with broad functional group tolerance. The methodology is amenable to a wide variety of carbon nucleophiles and can be utilized in late-stage functionalization of complex arenes. Furthermore, it is compatible with a new class of zwitterionic iodonium reagents, which gives access to phenols with an ortho-quaternary center. The diarylated products bear an ortho-iodo substituent that can be utilized in further transformations, including the formation of novel, functionalized six-membered cyclic iodonium salts.

Ortho-ester-substituted diaryliodonium salts enabled regioselective arylocyclization of naphthols toward 3,4-benzocoumarins

Cyclic annulation involving diaryliodonium salts is an efficient tool for the construction of two or more chemical bonds in a one-pot process. Ortho-functionalized diaryliodonium salts have showcased distinct reactivity in the exploration of benzocyclization or arylocyclization. With this strategy of ortho-ester-substituted diaryliodonium salts, herein, we utilized a copper catalyst to activate the C-I bond of diaryliodonium salts in the generation of aryl radicals, thus resulting in an annulation reaction with naphthols and substituted phenols. This approach yielded a diverse array of 3,4-benzocoumarin derivatives bearing various substituents.

EtOS2K as a C1 Source: Solvent- and Temperature-Controlled Selective Synthesis of Quinoline-2-thione and Quinoline-2-one Derivatives

Herein, we disclosed a highly chemoselective synthesis of quinoline-2-one and quinoline-2-thione derivatives using EtOS2K as the C1 source. Quinoline-2-one derivatives were synthesized selectively with NaCl as a catalyst in the solvent DMSO/H2O, while quinoline-2-thione derivatives were produced without the need for any catalyst in an environmentally friendly solvent EtOH/H2O. The reaction conditions were mild and had good functional group tolerance.

Syntheses, reactivity, and biological applications of coumarins

This comprehensive review, covering 2021-2023, explores the multifaceted chemical and pharmacological potential of coumarins, emphasizing their significance as versatile natural derivatives in medicinal chemistry. The synthesis and functionalization of coumarins have advanced with innovative strategies. This enabled the incorporation of diverse functional fragments or the construction of supplementary cyclic architectures, thereby the biological and physico-chemical properties of the compounds obtained were enhanced. The unique chemical structure of coumarine facilitates binding to various targets through hydrophobic interactions pi-stacking, hydrogen bonding, and dipole-dipole interactions. Therefore, this important scaffold exhibits promising applications in uncountable fields of medicinal chemistry (e.g., neurodegenerative diseases, cancer, inflammation).

Selective S-arylation of thiols with o-OTf-substituted diaryliodonium salts toward diarylsulfides

In contrast to the previously reported intramolecular aryl migration, we present the selective sulfenylation of ortho-trifluoromethanesulfonate (OTf) substituted diaryliodonium salts with thiols. As such, diarylsulfides bearing vicinal OTf groups were synthesized in good yields. The unique reactivity of the vicinal OTf group and the sulfur atom in arylsulfides offers further transformations.

"Alkene-to-Alkene" Difunctionalization of Enaminones for the Synthesis of Polyfunctionalized Alkenes by Transition-Metal-Free C-H and C-N Bond Transformation

The three-component reactions of enaminones, disulfides, and alcohols for the synthesis of polyfunctionalized alkenes have been realized via the C-H and C-N bond transformation on enaminones. The reactions proceed in a novel "alkene-to-alkene" difunctionalization mode without using any transition metal. The application of the alkene products in the synthesis of divergent sulfenyl heteroaryls, including sulfenylated pyrazoles, pyrimidines, and isoxazoles, via simple annulation has also been verified.

Synthesis of Complex Diarylamines through a Ring-Opening Difunctionalization Strategy

The diarylation and skeletal diversification of unstrained cyclic amines was exploited to expand and modify the favorable properties of this important substrate class with pivotal roles in drug discovery. Cyclic amines were employed in the synthesis of a novel class of amino-substituted diaryliodonium salts, which were converted to highly functionalized diarylamines through an atom-efficient one-pot N-arylation/ring opening reaction with external nucleophiles. The reaction proceeds through in situ formation of a diarylammonium intermediate that undergoes a nucleophilic ring opening by cleavage of the strong C-N bond. A wide variety of diarylamines was obtained through introduction of two different aryl groups of varied electronics, and the retained iodo-substituent enables downfield diversifications of the products. More than 20 nucleophiles, including amines, phenols, carboxylic acids, thiols and halides, were alkylated with high functional group tolerance, and the strategy proved efficient also in in late-stage functionalization of natural products and pharmaceuticals.

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.

Synthesis of Functionalized Pyrrolidinone Scaffolds via Smiles-Truce Cascade

Arylsulfonamides have been found to react with cyclopropane diesters under simple base treatment to give α-arylated pyrrolidinones. This one-pot process comprises three steps: nucleophilic ring-opening of the cyclopropane, reaction of the resulting enolate in a Smiles-Truce aryl transfer, and lactam formation. The reaction represents a new, operationally simple approach to biologically active pyrrolidinones and expands Smiles-Truce arylation methods to encompass sp3 electrophilic centers in cascade processes.

Diversification of Complex Diaryl Ethers via Diaryliodonium Intramolecular Aryl Rearrangement

In this study, we present an efficient site-selective O-arylation method applicable to a broad range of complex arenes involving intramolecular aryl rearrangement. The reaction was facilitated by diaryliodonium salts bearing vicinal trifluoromethanesulfonate (OTf) groups. The procedure was initiated with selective C-H bond activation of arenes, which were then converted into diaryl ethers through nucleophilic aromatic substitution (SNAr). This synthetic method successfully affords complex diaryl ether derivatives, showcasing its practicality for the diversification of functionalized arenes and pharmaceutical agents.

Metal-free and atom-efficient protocol for diarylation of selenocyanate by diaryliodonium salts

We developed an atom- and reaction mass efficient strategy for the preparation of diarylselenides using iodonium salts as reactants. The developed approach allows the obtaining of diarylselenides from the corresponding trimethoxyphenyl-substituted iodonium salts via a two-step one-pot reaction sequence. The proposed metal-free methodology is based on the involvement of both iodonium aryl groups for diarylation.

One-Pot, Three-Component Assembly of Sulfides Using a Sulfoxide Reagent as a Sulfur Dication Equivalent

We report a one-pot, three-component synthesis of sulfides by exploiting a sulfoxide reagent as a formal sulfur dication equivalent. Our protocol consists of three simple chemical operations involving two Grignard reagents and trimethylsilyl chloride (TMSCl) to sequentially form sulfenate anions, sulfenate esters, and sulfides. We demonstrate a wide range of Grignard reagents to be coupled, thereby allowing the modular, thiol-free synthesis of sulfides including dialkenyl and alkenyl-alkynyl sulfides.

DBDMH-Promoted Methylthiolation in DMSO: A Metal-Free Protocol to Methyl Sulfur Compounds with Multifunctional Groups

Organic thioethers play an important role in the discovery of drugs and natural products. However, the green synthesis of organic sulfide compounds remains a challenging task. The convenient and efficient synthesis of 5-alkoxy-3-halo-4-methylthio-2(5H)-furanones from DMSO is performed via the mediation of 1,3-dibromo-5,5-dimethylhydantoin (DBDMH), affording a facile route for the sulfur-functionalization of 3,4-dihalo-2(5H)-furanones under transition metal-free conditions. This new approach has demonstrated the functionalization of non-aromatic Csp2-X-type halides with unique structures containing C-X, C-O, C=O and C=C bonds. Compared with traditional synthesis methods using transition metal catalysts with ligands, this reaction has many advantages, such as the lower temperature, the shorter reaction time, the wide substrate range and good functional group tolerance. Notably, DMSO plays multiple roles, and is simultaneously used as an odorless methylthiolating reagent and safe solvent.