Oxidation reactions are vital tools in synthetic organic chemistry. Oxidation of organic species such as alcohols, phenols, aldehydes and ketones provides synthetically valuable organic compounds, especially synthetic intermediates for several biologically active compounds. Some of these synthetic intermediates have shown their synthetic utility in the total synthesis of natural products.
View Article and Find Full Text PDFWe have developed transition-metal-free synthetic methodologies for dibenzoxazepinones utilizing salicylamides as starting materials and employing two distinct types of successive hypervalent iodine-mediated arylocyclizations. This synthetic protocol encompasses selective phenol -arylation of salicylamides with diaryliodonium salts, followed by electrophilic aromatic amination utilizing chemically or electronically generated hypervalent iodine reagents in the second stage of the process.
View Article and Find Full Text PDFHerein, we report the development of metal-free one/two-pot procedures for the synthesis of benzo[]isoxazol-3(1)-one (benzisoxazolone) heterocycles by designing diaryliodonium salts featuring -ester or nitrile functional groups. These react smoothly with protected hydroxylamines under mild conditions to produce -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.
View Article and Find Full Text PDFChem Commun (Camb)
September 2024
We describe the transition-metal-free coupling for polyfluoroalkoxy arenes using polyfluoroalkoxy borates, which serve as counterions to diaryliodonium salts and transferring mediators of polyfluoroalkoxy groups. This strategy demonstrates high functional group compatibility owing to the low nucleophilicity of the borate mediator, thus offering a practical approach for synthesizing diverse polyfluoroalkoxy arenes.
View Article and Find Full Text PDFAn efficient metal-free, triflic acid-promoted intramolecular Friedel-Crafts-type carbocyclization of alkenylated biphenyl derivatives is discussed. This method provides an elegant route for the construction of 9,10-dihydrophenanthrenes of biological significance in good to excellent yields. The carbocyclization reaction is likely to proceeds via activation of terminal C[bond, double bond]C bond of alkenylated biphenyl derivatives followed by subsequent aromatic electrophilic substitution to give desired carbocyclic products.
View Article and Find Full Text PDFα-Fluorinated aryl esters pose a challenge in synthesis via -arylation of α-fluorinated carboxylates owing to their low reactivities. This limitation has been addressed by combining a silver catalyst with aryl(trimethoxyphenyl)iodonium tosylates to access α-fluorinated aryl esters. We envision that the catalytic system involves high-valent aryl silver species generated via the oxidation of silver(I) salt.
View Article and Find Full Text PDFDiaryliodonium(III) salts are versatile reagents that exhibit a range of reactions, both in the presence and absence of metal catalysts. In this study, we developed efficient synthetic methods for the preparation of aryl(TMP)iodonium(III) carboxylates, by reaction of (diacetoxyiodo)arenes or iodosoarenes with 1,3,5-trimethoxybenzene in the presence of a diverse range of organocarboxylic acids. These reactions were conducted under mild conditions using the trimethoxyphenyl (TMP) group as an auxiliary, without the need for additives, excess reagents, or counterion exchange in further steps.
View Article and Find Full Text PDFThis review summarizes the structural and synthetic aspects of heterocyclic molecules incorporating an atom of a hypervalent main-group element. The term "hypervalent" has been suggested for derivatives of main-group elements with more than eight valence electrons, and the concept of hypervalency is commonly used despite some criticism from theoretical chemists. The significantly higher thermal stability of hypervalent heterocycles compared to their acyclic analogs adds special features to their chemistry, particularly for bromine and iodine.
View Article and Find Full Text PDFTo prepare complicated organic molecules, straightforward, sustainable, and clean methodologies are urgently required. Thus, researchers are attempting to develop imaginative approaches. Metal-catalyzed multicomponent reactions (MCRs) offer optimal molecular diversity, high atomic efficiency, and energy savings in a single reaction step.
View Article and Find Full Text PDFThe chemistry of hypervalent iodine reagents has now become quite valuable due to the reactivity of these compounds under mild reaction conditions and their resemblance in chemical properties to transition metals. The environmentally friendly nature of these reagents makes them suitable for Green Chemistry. Reagents with a dual nature, such as iodine(III) reagents, are capable electrophiles, while iodine(V) reagents are known for their strong oxidant behavior.
View Article and Find Full Text PDF1,3-Dipolar cycloaddition through in situ generation of azomethine ylide provides a straightforward and critically important sustainable approach for access to diverse pyrrolidine chemical space. Herein, we developed a metal-free AcOH-activated 1,3-dipolar cycloaddition protocol that permits the synthesis of uncommon pyrrolidine cycloadducts with excellent diastereoselectivity. The challenging substrates of 3-formylchromone, glycine ester.
View Article and Find Full Text PDFC-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.
View Article and Find Full Text PDFTransition metal-catalyzed direct oxidative coupling reactions via C-H bond activation have emerged as a straightforward strategy for the construction of complex molecules in organic synthesis. The direct transformation of C-H bonds into carbon-carbon and carbon-heteroatom bonds renders the requirement of prefunctionalization of starting materials and, therefore, represents a more efficient alternative to the traditional cross-coupling reactions. The key to the unprecedented progress made in this area has been the identification of an appropriate oxidant that facilitates oxidation and provides heteroatom ligands at the metal center.
View Article and Find Full Text PDFThe chemistry of polyvalent iodine compounds has piqued the interest of researchers due to their role as important and flexible reagents in synthetic organic chemistry, resulting in a broad variety of useful organic molecules. These chemicals have potential uses in various functionalization procedures due to their non-toxic and environmentally friendly properties. As they are also strong electrophiles and potent oxidizing agents, the use of hypervalent iodine reagents in palladium-catalyzed transformations has received a lot of attention in recent years.
View Article and Find Full Text PDFIodine(III) reagents have attracted chemical relvance in organic synthesis by their use as safe, non-toxic, green and easy to handle reagents in different transformations. These characteristics make them important alternatives to procedures involving hazardous and harsh reaction conditions. Their versatility as oxidants has been exploited in the functionalization of different aromatic cores, which allow the introduction of several groups.
View Article and Find Full Text PDFHigh reactivity of trimethoxyphenyl (TMP)-iodonium(III) acetate for phenol -arylation was achieved. It was first determined that the TMP ligand and acetate anion cooperatively enhance the electrophilic reactivity toward phenol oxygen atoms. The proposed method provides access to various diaryl ethers in significantly higher yields than the previously reported techniques.
View Article and Find Full Text PDFSince 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 complex molecules in short steps. This focus review summarizes the double functionalization of carbon-iodine(III) and carbon-hydrogen bonds using diaryliodonium(III) salts.
View Article and Find Full Text PDFChem Pharm Bull (Tokyo)
February 2022
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)-H bonds directly to C(sp)-N bonds, and this direct approach to C-N bond formation offers effective access to benzolactams.
View Article and Find Full Text PDFA remarkable growth in hypervalent iodine-mediated oxidative transformations as stoichiometric reagents as well as catalysts has 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.
View Article and Find Full Text PDFThe 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.
View Article and Find Full Text PDFFunctionalized 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-arylation of halopurines, which possess a substituent at the N-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 C-arylations and SAr reactions of N-substituted chloropurines in aromatic and heteroatom nucleophiles promoted by triflimide (TfNH) in fluoroalcohol.
View Article and Find Full Text PDFNucleophilic aromatic substitution (SAr) reactions can provide metal-free access to synthesize monosubstituted aromatic compounds. We developed efficient SAr conditions for -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 SAr reaction to generate highly functionalized PTH derivatives with potential applicability as photocatalysts for the reduction of carbon-halogen bonds.
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