PubMed Journals Articles About "Selective Alkylation Polarity Match Based Cross Coupling" RSS

13:01 EST 16th December 2018 | BioPortfolio

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Showing "Selective alkylation polarity match based cross coupling" PubMed Articles 1–25 of 40,000+

Designing for Cross-coupling Reactions Using Aryl(trialkyl)silanes.

Organo(trialkyl)silanes have advantages in view of stability, low toxicity, solubility, handling, and ready availability compared with heteroatom-substituted silanes. On the other hand, cross-coupling with organo(trialkyl)silanes has been limited probably because of the exceeding robustness. Thus, a practical cross-coupling method with organo(trialkyl)silanes has been a long-standing challenging research target. This article discusses the designing how to use aryl(trialkyl)silanes for the cross-coupling. A ...

Oxidative Cross-Coupling of Boron and Antimony Nucleophiles via Palladium(I).

The use of an isolatable, monomeric Pd(I) complex as a catalyst for the oxidative cross-coupling of aryl-antimony and aryl-boron nucleophiles is reported. This reaction tolerates a wide variety of substrates, with >20:1 selectivity for cross-coupled products. This strategy offers a new approach to achieving the selective cross-coupling of nucleophiles.

Cross-Coupling of Amides with Alkylboranes via Nickel-Catalyzed C-N Bond Cleavage.

A protocol for the nickel-catalyzed alkylation of amides was established. The use of alkylboranes as nucleophilic partners allowed the use of mild reaction conditions and compatibility of various functional groups with respect to both coupling partners. The catalytic alkylation proceeded selectively at the amides in the presence of other functional groups as well as other carboxylic acid derived moieties.

Well-Defined Palladium(II)-NHC Precatalysts for Cross-Coupling Reactions of Amides and Esters by Selective N-C/O-C Cleavage.

Transition-metal-catalyzed cross-coupling reactions represent a most powerful tool for the rapid construction of C-C and C-X bonds available to synthetic chemists. Recently, tremendous progress has been made in the burgeoning area of cross-coupling reactions of amides and esters enabled by regio- and chemoselective acyl C-X (X = N, O) cleavage using well-defined Pd(II)-NHC complexes. The use of N-heterocyclic carbenes as ligands in palladium-catalyzed cross-couplings permits reactions of amides and esters t...

Oxidative R1-H/R2-H Cross-Coupling with Hydrogen Evolution.

Oxidative R1-H/R2-H cross-coupling with hydrogen evolution serves as one of the most atom-economical methods for constructing new chemical bonds. This re-action strategy avoids substrate prefunctionalization steps in traditional cross-coupling reactions. Besides, hydrogen gas, which is recognized as a source of green energy, is the only byproduct during the reaction pro-cess. The major challenge in this reaction strategy is to achieve selective bond formation and hydrogen evolu-tion at the same time. Over t...

Understanding Thermal and Photochemical Aryl-Aryl Cross-Coupling by the Au(I)-AuIII) Redox Couple.

A systematic mechanistic investigation has been performed for the gold(I)/gold(III) redox-controlled aryl-aryl cross-coupling reaction using both thermal and photochemical approach. Electronically deprived arenes and electron-rich arenes are considered as the coupling partners of the reaction. Based on transition state modeling and distortion-interaction analyses, it is shown that Au(I) prefers to react with the electro-deficient arene whereas Au(III) likes to activate electro-rich one. This orthogonal reac...

Upgrading Cross-Coupling Reactions for Biaryl Syntheses.

Transition-metal catalyzed cross-coupling reactions have emerged as a powerful tool for constructing biaryl compounds. Aryl halides and aryl metallic reagents (typically prepared from aryl halides) are used as coupling partners. It would be desirable to replace either aryl halide or aryl metallic reagents used in cross-couplings reactions with more readily available surrogates. Oxidative dehydrogenative cross-coupling between two different "inert" aryl C-H bonds represents an ideal system that would revolut...

Palladium/NHC (NHC = N-Heterocyclic Carbene)-Catalyzed B-Alkyl Suzuki Cross-Coupling of Amides by Selective N-C Bond Cleavage.

A highly chemoselective, palladium-NHC (NHC = N-heterocyclic carbene)-catalyzed, direct cross-coupling between B-sp-alkyl reagents and activated amides by N-C(O) cleavage is reported. Palladium-NHC precatalysts promote chemoselective alkylations of amides that are inaccessible by applying strong organometallic reagents. Various amides, including challenging primary amides after direct and site-selective N, N-di-Boc activation, are compatible with this method. The potential of this mild protocol is demonstra...

Nitrosonium ion catalysis: aerobic, metal-free cross-dehydrogenative carbon-heteroatom bond formation.

Catalytic cross-dehydrogenative coupling of heteroarenes with thiophenols and phenothiazines has been developed under mild and environmentally benign reaction conditions. For the first time, NOx+ was applied for catalytic C-S and C-N bond formation. A comprehensive scope for the C-H/S-H and C-H/N-H cross-dehydrogenative coupling was demonstrated with >60 examples. The sustainable cross-coupling conditions utilize ambient oxygen as the terminal oxidant, while water is the sole by-product.

Diastereodivergent Reductive Cross Coupling of Alkynes through Tandem Catalysis: Z- and E-Selective Hydroarylation of Terminal Alkynes.

A diastereodivergent hydroarylation of terminal alkynes is accomplished using tandem catalysis. The hydroarylation allows highly selective synthesis of both E and Z diastereoisomers of aryl alkenes, from the same set of starting materials, using the same combination of palladium and copper catalysts. The selectivity is controlled by simple changes in the stoichiometry of the alcohol additive. The hydroarylation has excellent substrate scope and can be accomplished in the presence of various classes of compo...

Non-Directed Cross-Dehydrogenative (Hetero)arylation of Allylic C(sp3)-H bonds enabled by C-H activation.

Herein, we report the selective, non-directed and cross-dehydrogenative coupling of allylic C(sp3)-H bonds with C(sp2)-H bonds of (hetero)arenes that is enabled by C-H activation. The developed methodology employs the abundant chemical feedstocks of olefins and (hetero)arenes and could be applied in late-stage functionalization reactions of pharmaceuticals. Furthermore, in contrast to established cross-dehydrogenative Heck-type reactions, the discovered system exclusively delivers the allylic C-C coupling p...

Direct β-Alkylation of Ketones and Aldehydes via Pd-Catalyzed Redox Cascade.

We report a direct β-alkylation of ketones and aldehydes with simple alkyl bromides through a Pd-catalyzed redox-cascade strategy. The use of a Cu co-catalyst is important for improved efficiency. The reaction is redox-neutral, without the need for strong acids or bases. Both cyclic and acyclic ketones, as well as α-branched aldehydes, are suitable substrates for coupling with secondary and tertiary alkyl bromides. Concise formal synthesis of Zanapezil is achieved using this β-alkylation method.

Cu(I)-Catalyzed Cross-Coupling of Diazo Compounds with Terminal Alkynes: An Efficient Access to Allenes.

Cu(I)-catalyzed reaction of diazo compounds generates a Cu(I)-carbene intermediate that undergoes diverse transformations. In the past few years, the diazo compounds (or their precursor N-tosylhydrazones) have been established as cross-coupling partners under transition-metal catalysis, affording various organic compounds. Particularly the breakthrough has been made in allene synthesis by Cu(I)-catalyzed carbene coupling with terminal alkynes. Moreover, the Cu(I)-catalyzed coupling reaction of diazo compoun...

Synthesis of Aryl Trimethylstannane via BF3·OEt2-mediated Cross-Coupling of Hexaalkyl Distannane Reagent with Aryl Triazene at Room Temperature.

BF3·OEt2-mediated cross-coupling of (SnMe3)2 with aryl triazene offers a new strategy for the synthesis of aryl stannane. A variety of synthetically useful aryl trimethylstannanes were produced in moderate to good yields with this metal-free approach. One-pot sequential Stille cross-coupling with different aryl bromides provides a short entry to both symmetrical and unsymmetrical biaryl compounds.

Intermediates and Mechanism in Iron-Catalyzed Cross-Coupling.

Iron-catalyzed cross-coupling reactions have attracted significant research interest, as they offer numerous favorable features compared with cross-coupling reactions with precious metal catalysis. While this research has contributed to an empirical understanding of iron-catalyzed cross-coupling, the underlying fundamental mechanisms of reaction and structures of catalytically active species have remained poorly defined. The lack of such detail can be attributed to the difficulties associated with studying ...

Beyond Friedel and Crafts: Directed Alkylation of C-H Bonds in Arenes.

The alkylation of arenes is one of the most fundamental transformations in chemical synthesis leading to privileged scaffolds in many areas of science. Classical methods for the introduction of alkyl groups to arenes are mostly based on the Friedel-Crafts reaction, radical additions, metallation or pre-functionalization of the arene: these methods however suffer from limitations in scope, efficiency and selectivity. Moreover, they are based on the innate reactivity of the starting arene, favoring the alkyla...

Manganese Catalyzed Regioselective C-H Alkylation: Experiment and Computation.

A new efficient manganese-catalyzed selective C2-alkylation of indoles via carbenoid insertion has been achieved. The newly developed C-H functionalization protocol provides access to diverse products and shows good functional group tolerance. Mechanistic and computational studies support the formation of a Mn(CO) acetate complex as the catalytically active species.

Nickel-catalyzed coupling reaction of alkyl halides with aryl Grignard reagents in the presence of 1,3-butadiene: mechanistic studies of four-component coupling and competing cross-coupling reactions.

We describe the mechanism, substituent effects, and origins of the selectivity of the nickel-catalyzed four-component coupling reactions of alkyl fluorides, aryl Grignard reagents, and two molecules of 1,3-butadiene that affords a 1,6-octadiene carbon framework bearing alkyl and aryl groups at the 3- and 8-positions, respectively, and the competing cross-coupling reaction. Both the four-component coupling reaction and the cross-coupling reaction are triggered by the formation of anionic nickel complexes, wh...

Direct C-OH/P(O)-H dehydration coupling forming phosphine oxides.

A t-BuONa-mediated C-OH/P(O)-H cross dehydration coupling to produce alkylphosphine oxides is developed. This reaction employed readily available alcohols and P(O)-H compounds as the starting materials, providing an efficient alternative method for constructing sp3 C-P bonds. A reasonable reaction path involving dehydration and subsequent regio-selective hydrophosphorylation of the resulting alkenes was proposed.

Organocatalytic decarboxylative alkylation of N-hydroxy-phthalimide esters enabled by pyridine-boryl radicals.

The decarboxylative alkylation of N-hydroxyphthalimide (NHPI) based reactive esters with olefins has been achieved via an organocatalytic strategy. Control experiments and density functional theory calculations suggest that these reactions involve a boryl-radical mediated decarboxylation pathway, which is different from the single electron transfer involved in decarboxylative alkylation reactions reported previously. This metal-free decarboxylative alkylation reaction features good functional compatibility,...

Recent Advances in Alkyl Carbon-Carbon Bond Formation by Nickel/Photoredox Cross-Coupling.

The union of photoredox and nickel catalysis has resulted in a renaissance in radical chemistry as well as in the use of nickel-catalyzed transformations, specifically for carbon-carbon bond formation. Collectively, these advances address the longstanding challenge of late-stage cross-coupling of functionalized alkyl fragments. Empowered by the notion that photocatalytically-generated alkyl radicals readily undergo capture by Ni complexes, wholly new feedstocks for cross-coupling have been realized. Herein,...

Polarised Organisation of the Cytoskeleton: Regulation by Cell Polarity Proteins.

Polarity is one of the fundamental properties displayed by living organisms. In metazoans, cell polarity governs developmental processes and plays an essential role during maintenance of forms of tissues as well as their functions. The mechanisms of establishment and maintenance of cell polarity have been investigated extensively in the last two decades. This has resulted in identification of "core cell polarity modules" that control anterior-posterior, front-rear and apical-basal polarity across various ce...

Cavity-Mediated Coherent Coupling between Distant Quantum Dots.

Scalable architectures for quantum information technologies require one to selectively couple long-distance qubits while suppressing environmental noise and cross talk. In semiconductor materials, the coherent coupling of a single spin on a quantum dot to a cavity hosting fermionic modes offers a new solution to this technological challenge. Here, we demonstrate coherent coupling between two spatially separated quantum dots using an electronic cavity design that takes advantage of whispering-gallery modes i...

Palladium-Catalyzed Thiomethylation via a Three-Component Cross-Coupling Strategy.

In this report, the combination of masked inorganic sulfur and dimethyl carbonate was designed to achieve thiomethylated cross coupling of aryl chlorides. Remarkably, this powerful strategy realized thiomethylation of nucleosides bearing unprotected ribose, chloride-containing pharmaceuticals with late-stage coupling, and herbicides possessing multiple heteroatoms and steric hindrance. Moreover, this protocol is practically amenable to multigram-scale synthesis with a lower catalysis loading and a higher yi...

More diversity in epithelial cell polarity: A fruit flies' gut feeling.

Multicellular animals face the principle challenge to deal with two distinct compartments: the internal organismal compartment and the external environment. This challenge is met by the differentiation of cell sheets into epithelia, which provide a dynamic barrier in tissues, organs, and organisms. Cell polarity is key to all functions of epithelia, and compromising polarity causes many severe diseases. Within the past 20 years, research on Drosophila melanogaster discovered a conserved molecular machinery ...

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