Aryl Triflates Research Articles

Palladium-catalyzed double-carbonylative cyclization of propargyl alcohols and aryl triflates to expedite construction of 4-aroyl-furan-2(5H)-ones

A palladium-catalyzed double-carbonylative cyclization of propargyl alcohols and aryl triflates has been developed. Various 4-aroyl-furan-2(5H)-one scaffolds were produced in good yields with Cr(CO)6 as the CO source.

Asymmetric Intermolecular Heck Reaction of Aryl Halides by Pd-histidine Organocatalysts

Extensive studies of asymmetric intermolecular Heck reaction are described and provide a deeper insight into histidine-catalyzed. In particular, aspects of enantio- as well as diastereoselectivity of these reactions are discussed. As the first report, we synthesized five histidine-based organocatalyts including histidine as a well-defined and biodegradable natural structure alone and in combination with 2,4,6-trichloro-1,3,5-triazine, benzene-1,3-diamine, dimethyl malonate and dimeric structure applied in the asymmetric intermolecular Heck reaction of aryl halides; their efficiency was compared to each other’s. These phosphine-free palladium catalysts were found as efficient catalytic system which provided the superior efficiency with excellent yields, regioselectivity and enantioselectivity. In these among, histidine with 2,4,6-trichloro-1,3,5-triazine which generate the star like molecule palladium catalyst gave the best activity in asymmetric intermolecular Heck reaction with excellent yields and good regio- and enantioselectivity under mild reaction conditions. The asymmetric intermolecular Heck reaction has been limited to aryl and vinyl triflates or aryl iodide in the rare reports of available Pd catalysts. Herein, we extend the reaction to aryl bromides. In addition, the scope of reaction was examined in two different techniques: conventional heating and microwave irradiation and compared. For the first time, microwave irradiation sintering is successfully used for this reaction. Comparison of catalytic activities of our catalyst (Pd/His) with literature examples confirmed our success.

Palladium-Catalyzed Asymmetric Heck Coupling of Aryl Triflates and Alkynes

Palladium-Catalyzed Asymmetric Heck Coupling of Aryl Triflates and Alkynes

Catalytic Reductions Without External Hydrogen Gas: Broad Scope Hydrogenations with Tetrahydroxydiboron and a Tertiary Amine.

Facile reduction of aryl halides with a combination of 5% Pd/C, B2(OH)4, and 4-methylmorpholine is reported. Aryl bromides, iodides, and chlorides were efficiently reduced. Aryl dihalides containing two different halogen atoms underwent selective reduction: I over Br and Cl, and Br over Cl. Beyond these, aryl triflates were efficiently reduced. This combination was broadly general, effectuating reductions of benzylic halides and ethers, alkenes, alkynes, aldehydes, and azides, as well as for N-Cbz deprotection. A cyano group was unaffected, but a nitro group and a ketone underwent reduction to a low extent. When B2(OD)4 was used for aryl halide reduction, a significant amount of deuteriation occurred. However, H atom incorporation competed and increased in slower reactions. 4-Methylmorpholine was identified as a possible source of H atoms in this, but a combination of only 4-methylmorpholine and Pd/C did not result in reduction. Hydrogen gas has been observed to form with this reagent combination. Experiments aimed at understanding the chemistry led to the proposal of a plausible mechanism and to the identification of N,N-bis(methyl-d 3)pyridine-4-amine (DMAP-d 6) and B2(OD)4 as an effective combination for full aromatic deuteriation.

Pd-Catalyzed Enantioselective Heck Reaction of Aryl Triflates and Alkynes.

The first palladium-catalyzed asymmetric Heck reaction between aryl triflates and alkynes to give trisubstituted allenes with high er under mild reaction conditions is described. The key to the success is the discovery and fine-tuning of the different N-substituents of Xu-Phos, which ensure the enantioselectivity and reactivity. Synthetic transformation of the chiral allenes with high chirality transfer was also demonstrated.

Ni-Catalyzed Reductive Cyanation of Aryl Halides and Phenol Derivatives via Transnitrilation.

Herein, we report a Ni-catalyzed reductive coupling for the synthesis of benzonitriles from aryl (pseudo)halides and an electrophilic cyanating reagent, 2-methyl-2-phenyl malononitrile (MPMN). MPMN is a bench-stable, carbon-bound electrophilic CN reagent that does not release cyanide under the reaction conditions. A variety of medicinally relevant benzonitriles can be made in good yields. Addition of NaBr to the reaction mixture allows for the use of more challenging aryl electrophiles such as aryl chlorides, tosylates, and triflates. Mechanistic investigations suggest that NaBr plays a role in facilitating oxidative addition with these substrates.

Practical C–P bond formation via heterogeneous photoredox and nickel synergetic catalysis

AbstractAn efficient C&–P bond formation reaction was developed by virtue of the synergetic catalysis strategy by merging heterogeneous photocatalysis and nickel catalysis. This platform utilizing cadmium sulfide semiconductors as heterogeneous photocatalysts and nickel complexes as transition metal catalysts provided a variety of organophosphorus compounds from readily available aryl and vinyl halides, as well as aryl triflates, with generally a good-to-excellent reaction efficiency (31 examples, 46%-98% yields). The current protocol features mild reaction conditions, a broad substrate scope, recyclability of photocatalysts, and inexpensive catalysts, thus defining the practical and economic proprieties of the present catalyst system.

NHC Ligand-Enabled, Palladium-Catalyzed Non-Directed C(sp3)–H Carbonylation To Access Indanone Cores

A palladium-catalyzed C(sp3)–H carbonylation of alkylated aryl triflates or bromides under 1 atm of CO has been developed, in which no directing group or oxidant was required. The essence of this r...

Enantioselective Conjugate Addition of Aryl Halides and Triflates to Electron-Deficient Olefins via Nickel- and Rhodium-Catalyzed Sequential Relay Reactions.

Asymmetric conjugate addition of aryl halides or aryl triflates to electron-deficient olefins was realized by sequential Miyaura borylation and Hayashi-Miyaura conjugate addition in one pot. A nickel-catalyzed borylation of aryl halides or triflates and a rhodium-chiral diene complex catalyzed enantioselective conjugate addition was executed as a pair of relay reactions as a more efficient and greener protocol.

Rapid and Efficient Approaches for Synthesis of Some New Aryl Propionic Acid Derivatives and In–Vivo Anti‐Diabetic Screening of Selected Compounds

AbstractA series of some new aryl propionic acid derivatives as 2‐(6‐(substituted phenylethynyl)‐2,3‐dihydrobenzofuran‐3‐yl)acetic acids were synthesized. The targeted molecules were prepared by using techniques such as efficient and high‐performance autoclave hydrogenation to reduce highly stable π‐electron system of furan ring and microwave‐assisted rapid Sonogashira Cross‐Coupling reaction between aryl triflate derivatives and substituted aryl acetylenes. The anti‐diabetic screening of selected compounds was performed by using alloxan‐induced diabetic model. The studies include acute and chronic toxicity, effectiveness, change in the behavioral pattern and change in glucose level of the tested animals. The compound 2‐(6‐((4‐ethylphenyl)ethynyl)‐2,3‐dihydrobenzofuran‐3‐yl)acetic acid exhibited maximum anti‐hyperglycemic properties. All the synthesized compounds were characterized by spectroscopic techniques such as 1H‐NMR, 13C‐NMR, IR, Mass spectrometry and single crystal XRD (MTS‐201).

Cobalt-Catalyzed Cross-Coupling Reactions of Aryl Triflates and Lithium Arylborates.

A catalyst system comprising CoCl2/IAd·HBF4 enables the Suzuki-Miyaura cross-coupling reaction of a broad range of aryl triflates and arylboronic esters that are activated by n-butyllithium.

Preparation and Synthetic Applications of [2.2]Paracyclophane Trifluoroborates: An Efficient and Convenient Route to Nucleophilic [2.2]Paracyclophane Cross‐Coupling Building Blocks

We report the synthesis of [2.2]paracyclophane (PCP) trifluoroborate building blocks that can be used for the incorporation of the PCP moiety into a wide range of (hetero)aryl chlorides, bromides and triflates by a Pd(II)/RuPhos mediated Suzuki–Miyaura cross‐coupling reaction. The PCP trifluoroborate species are bench stable with extended shelf life and easily accessible on a multigram scale by a two‐step synthesis from commercially available PCP. They can be handled conveniently without special precautions, thus overcoming many of the limitations of other PCP cross‐coupling reagents. Additionally, a high yielding regioselective monolithiation/borylation protocol for the synthesis of pseudo‐para and pseudo‐ortho PCP halotrifluoroborates and their subsequent Suzuki–Miyaura cross‐coupling are described.

Pd-Catalyzed Alkene Difunctionalization Reactions of Enolates for the Synthesis of Substituted Bicyclic Cyclopentanes.

Palladium-catalyzed alkene difunctionalization reactions between alkenes bearing tethered aryl or alkenyl triflates and enolate nucleophiles are described. The transformations form two C-C bonds, a ring, and up to two stereocenters, while producing substituted cyclopentane derivatives that contain appended carbonyl functionality. Products are formed with up to >20:1 diastereoselectivity, and formation of sterically congested bonds between quaternary carbon atoms is feasible.

Sequentially Pd/Cu‐Catalyzed Alkynylation‐Oxidation Synthesis of 1,2‐Diketones and Consecutive One‐Pot Generation of Quinoxalines

We report a simple and efficient one‐pot synthesis of 1,2‐diketones by concatenation of two Pd/Cu‐catalyzed processes: Pd0/CuI‐catalyzed Sonogashira coupling of terminal alkynes with aryl (pseudo)halides furnishes internal alkynes, which are directly transformed by PdII/CuII‐catalyzed Wacker‐type oxidation with DMSO and oxygen as dual oxidants to furnish 1,2‐diketones. With this efficient, catalyst economical process, various aryl iodides and triflates are efficiently transformed in high yields into symmetrically and unsymmetrically substituted 1,2‐diketones with various functional groups. This process can be readily extended to a consecutive one‐pot synthesis of quinoxalines in a diversity‐oriented fashion.

LiCl-Accelerated Multimetallic Cross-Coupling of Aryl Chlorides with Aryl Triflates.

While the synthesis of biaryls has advanced rapidly in the past decades, cross-Ullman couplings of aryl chlorides, the most abundant aryl electrophiles, have remained elusive. Reported here is the first general cross-Ullman coupling of aryl chlorides with aryl triflates. The selectivity challenge associated with coupling an inert electrophile with a reactive one is overcome using a multimetallic strategy with the appropriate choice of additive. Studies demonstrate that LiCl is essential for effective cross-coupling by accelerating the reduction of Ni(II) to Ni(0) and counteracting autoinhibition of reduction at Zn(0) by Zn(II) salts. The modified conditions tolerate a variety of functional groups on either coupling partner (42 examples), and examples include a three-step synthesis of flurbiprofen.

Direct Access to 1,1-Dicarbonyl Sulfoxonium Ylides from Aryl Halides or Triflates: Palladium-Catalyzed Carbonylation.

The synthesis of 1,1-dicarbonyl sulfoxonium ylides by palladium-catalyzed carbonylation of aryl halides or triflates with α-carbonyl sulfoxonium ylides has been developed for the first time. This method provides a general approach to synthetically useful 1,1-dicarbonyl sulfoxonium ylides in high efficiency. The protocol displays a wide substrate scope, showing that the resulting 1,1-dicarbonyl sulfoxonium ylides have been converted into the corresponding 1,3-dicarbonyl compounds.

Mechanism-Based Optimization of the Palladium-Catalyzed Amination of Aryl Triflates

Mechanism-Based Optimization of the Palladium-Catalyzed Amination of Aryl Triflates

Palladium-Catalyzed Visible-Light-Driven Carboxylation of Aryl and Alkenyl Triflates by Using Photoredox Catalysts.

A visible-light-driven carboxylation of aryl and alkenyl triflates with CO2 is developed by using a combination of Pd and photoredox catalysts. This reaction proceeds under mild conditions and can be applied to a wide range of substrates including acyclic alkenyl triflates.

One-Pot, Three-Aryne Cascade Strategy for Naphthalene Formation from 1,3-Diynes and 1,2-Benzdiyne Equivalents

Here we disclose a cascade strategy for naphthyne formation that capitalizes on the traditional benzyne generation (i.e., from an ortho-silyl aryl triflate) and the thermal hexadehydro-Diels-Alder (HDDA) reaction. In this transformation, three distinct aryne species work in tandem, two of which can be formally considered as a 1,2-benzidyne, and each undergoes a different type of trapping event. Many examples were explored by varying the naphthyne capture chemistry as well as the 1,2-benzdiyne equivalent. This strategy enables rapid construction of various naphthalene products and has potential for the synthesis of extended polycyclic arenes.

Pd-Catalyzed Alkene Difunctionalization Reactions of Malonate Nucleophiles: Synthesis of Substituted Cyclopentanes via Alkene Aryl-Alkylation and Akenyl-Alkylation.

The Pd-catalyzed coupling of malonate nucleophiles with alkenes bearing tethered aryl or alkenyl triflates is described. These alkene difunctionalization reactions afford malonate-substituted cyclopentanes that contain fused aryl or cycloalkenyl rings. The transformations generate a five-membered ring, two C-C bonds, and provide products bearing up to three stereocenters with good chemical yield and generally high diastereoselectivity.