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

23:57 EDT 23rd September 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...

Metal-free site selective cross-coupling of pyridines with secondary phosphine chalcogenides using acylacetylenes as oxidants.

Pyridines undergo site selective cross-coupling with secondary phosphine chalcogenides (oxides, sulfides, and selenides) in the presence of acylphenylacetylenes under metal-free mild conditions (70-75 °C, MeCN) to afford 4-chalcogenophosphoryl pyridines in up to 71% yield. In this new type of SNHAr reaction acylacetylenes act as oxidants, being stereoselectively reduced to the corresponding olefins of the E-configuration.

Palladium-Catalyzed Selective Mono-/Tetraacetoxylation of o-Carboranes with Acetic Acid via Cross Dehydrogenative Coupling of Cage B-H/O-H Bonds.

A selective mono-/tetraacetoxylation of o-carboranes with acetic acid via cross dehydrogenative coupling of cage B-H/O-H bonds has been developed, and a series of mono- and tetraacetoxylated o-carboranes have been synthesized with moderate to good yields as well as good selectivity. Mechanistic studies indicate that the acetoxyl originates from acetic acid directly, and a nucleophilic addition of Pd-oxo species and dehydration process is proposed.

Trimethylsilyl-Protected Alkynes as Selective Cross Coupling Partners in Ti-Catalyzed 2+2+1 Pyrrole Synthesis.

Trimethylsilyl (TMS)-protected alkynes serve as selective alkyne cross coupling partners in Ti-catalyzed [2+2+1] pyrrole synthesis. Reactions of TMS-protected alkynes with internal alkynes and azobenzene catalyzed by Ti imido catalysts yield pentasubstituted 2-TMS-pyrroles with greater than 90% selectivity over the other 9 possible pyrrole products. The steric and electronic effects of the TMS group have both been identified to play key roles in this highly selective pyrrole synthesis. This strategy provide...

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...

Design, Fabrication and Characterization of a MEMS-Based Three-Dimensional Electric Field Sensor with Low Cross-Axis Coupling Interference.

One of the major concerns in the development of three-dimensional (3D) electric field sensors (EFSs) is their susceptibility to cross-axis coupling interference. The output signal for each sensing axis of a 3D EFS is often coupled by electric field components from the two other orthogonal sensing axes. In this paper, a one-dimensional (1D) electric field sensor chip (EFSC) with low cross-axis coupling interference is presented. It is designed to be symmetrical, forming a pair of in-plane symmetrically-locat...

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...

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...

The N-Methylpyrrolidone (NMP) Effect in Iron-Catalyzed Cross-Coupling with Simple Ferric Salts and MeMgBr.

The use of N-methylpyrrolidone (NMP) as a co-solvent in ferric salt catalyzed cross-coupling reactions is crucial for achieving the highly selective, preparative scale formation of cross-coupled product in reactions utilizing alkyl Grignard reagents. Despite the critical importance of NMP, the molecular level effect of NMP on in-situ formed and reactive iron species that enables effective catalysis remains undefined. Herein, we report the isolation and characterization of a novel trimethyliron(II) ferrate s...

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...

Visible Light-Induced Nickel-Catalyzed Negishi Cross-Coupling. A New Approach to Exogenous Photosensitizer-free Photocatalysis.

The merging of photoredox and transition-metal catalysis has become one of the most attractive approaches for carbon-carbon bond formation. The procedure requires the use of two transition organometallic species, one of which acts as a photosensitizer and the other as a cross-coupling catalyst. We report here a new exogenous photosensitizer-free photocatalytic protocol that allows the formation of carbon-carbon bonds by direct acceleration of the well-known nickel-catalyzed Negishi cross-coupling using two ...

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,...

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...

In Situ Generation of Plasmonic Nanoparticles for Manipulating Photon-Plasmon Coupling in Microtube Cavities.

In situ generation of silver nanoparticles for selective coupling between localized plasmonic resonances and whispering-gallery-modes (WGMs) is investigated by spatially-resolved laser dewetting on microtube cavities. The size and morphology of the silver nanoparticles are changed by adjusting the laser power and irradiation time, which in turn effectively tune the photon-plasmon coupling strength. Depending on the relative position of the plasmonic nanoparticles spot and resonant field distribution of WGMs...

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