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

05:04 EDT 24th June 2018 | BioPortfolio

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Showing "Selective alkylation polarity match based cross coupling" PubMed Articles 1–25 of 39,000+

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.

Selective alkylation of T-T mismatched DNA using vinyldiaminotriazine-acridine conjugate.

The alkylation of the specific higher-order nucleic acid structures is of great significance in order to control its function and gene expression. In this report, we have described the T-T mismatch selective alkylation with a vinyldiaminotriazine (VDAT)-acridine conjugate. The alkylation selectively proceeded at the N3 position of thymidine on the T-T mismatch. Interestingly, the alkylated thymidine induced base flipping of the complementary base in the duplex. In a model experiment for the alkylation of th...

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...

Enantiospecific and Iterative Suzuki-Miyaura Cross-Couplings.

The Suzuki-Miyaura cross-coupling reaction has emerged as one of the most powerful methods for the construction of carbon-carbon bonds. Though most widely utilized for the synthesis of sp2-sp2 linkages, the use of this reaction to form stereochemistry-bearing sp2-sp3 bonds has received widespread attention over the past decade. This Perspective highlights approaches to the synthesis of enantioenriched molecules via the Suzuki-Miyaura reaction. Particular focus is placed on the use of enantiomerically enrich...

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...

Palladium/Copper Dual Catalysis for Cross-coupling of Aryl(trialkyl)silanes with Aryl Bromides.

Although aryl(trialkyl)silanes are apparently ideal organometalic reagents for the cross-coupling reaction due to robustness, low toxicity, solubility, and easy accessibility, they are generally an inert cross-coupling nucleophile. Disclosed herein is that a palladium/copper catalytic system achieves the desired cross-coupling of aryl-SiMe3, -SiEt3, -SiMe2(t-Bu), and -Si(i-Pr)3 with aryl bromides, allowing application to the sequential C-H and C-Si bond arylation of thiophenes and the synthesis of poly(thio...

Enantioselective Intermolecular C-O Bond Formation in the Desymmetrization of Diarylmethines Employing a Guanidinylated Peptide-Based Catalyst.

We report a series of enantioselective C-O bond cross-coupling reactions based on remote symmetry breaking processes in diarylmethine substrates. Key to the chemistry are multifunctional guanidinylated peptide-based ligands that allow highly selective, intermolecular Cu-catalyzed cross-coupling of phenolic nucleophiles. The scope of the process is explored, demonstrating efficiency for substrates with a range of electronic and steric perturbations to the nucleophile. Scope and limitations are also reported ...

Density Functional Theory Mechanistic Study of Boron-Catalyzed N-Alkylation of Amines with HCO2H: HCO2H Activation via Silylation Reaction.

New methodology for alkylation of amines is an intriguing issue in both academia and industry. Recently, several groups reported the metal-free B(C6F5)3-catalyzed N-alkylation of amines. But the mechanistic details of these important reactions are unclear. Herein, a computational study was performed to elucidate the mechanism of the N-alkylation of amines with formic acid catalyzed by Lewis acid B(C6F5)3 in the presence of hydrosilane. We found that the reaction is started with the activation of formic acid...

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...

Macroscopic Polarization from Antiferrodistortive Cycloids in Ferroelastic SrTiO_{3}.

Based on a first-principles based multiscale approach, we study the polarity P of ferroelastic twin walls in SrTiO_{3}. In addition to flexoelectricity, which was pointed out before, we identify two new mechanisms that crucially contribute to P: a direct "rotopolar" coupling to the gradients of the antiferrodistortive oxygen tilts, and a trilinear coupling that is mediated by the antiferroelectric displacement of the Ti atoms. Remarkably, the rotopolar coupling presents a strong analogy to the mechanism tha...

Nickel-Catalyzed Desymmetrizing Cross-Electrophile Coupling of Cyclic Meso-Anhydrides.

A Ni-catalyzed desymmetrizing cross-electrophile coupling of cyclic meso-anhydrides with aryl triflates has been successfully demonstrated. This is the only example using cyclic meso-anhydrides in cross-electrophile coupling reactions. A diverse array of valuable γ-keto acid building blocks can be generated under these conditions with excellent functional group tolerance and stereochemical fidelity.

Polarization-independent directional coupler and polarization beam splitter based on asymmetric cross-slot waveguides.

The polarization dependence of a directional coupler (DC) based on asymmetric cross-slot waveguides is investigated. Due to structural birefringence, the coupling behaviors of the quasi-TE and quasi-TM modes in the DC vary with the waveguide geometry. A polarization-independent directional coupler (PIDC) and polarization beam splitter (PBS) are proposed by tailoring the ratio of the coupling length for quasi-TE and quasi-TM modes. The simulated results show that the coupling lengths of the designed PIDC and...

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.

Interrogating Pd(II) anion metathesis using a bifunctional chemical probe: A transmetalation switch.

Ligand metathesis of Pd(II) complexes is mechanistically essential for cross-coupling. We present a study of halide→OH anion metathesis of (Ar)Pd(II) complexes using vinylBPin as a bifunctional chemical probe with Pd(II)-dependent cross-coupling pathways. We identify the variables that profoundly impact this event and allow control to be leveraged. This then allows control of cross-coupling pathways via promotion or inhibition of organoboron transmetalation, leading to either Suzuki-Miyaura or Mizoroki-He...

Highly Selective Dopamine D3 Receptor Antagonists with Arylated Diazaspiro Alkane Cores.

A series of potent and selective D3 receptor (D3R) analogues with diazaspiro alkane cores were synthesized. Radioligand binding of compounds 11, 14, 15a, and 15c revealed favorable D3R affinity (Ki = 12-25.6 nM) and were highly selective for D3R vs D3R (ranging from 264-905-fold). Variation of these novel ligand architectures can be achieved using our previously reported 10-20 minute benchtop C-N cross-coupling methodology, affording a broad range of arylated diazaspiro pre-cursors.

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 ...

Ultracompact, high extinction ratio polarization beam splitter-rotator based on hybrid plasmonic-dielectric directional coupling.

A polarization beam splitter-rotator based on asymmetric directional coupling is proposed. An ultrashort cross-polarization coupling length of 7.7 μm is achieved by manipulating the optical field distribution via the plasmonic effect, which is the shortest one reported so far, to the best of our knowledge. At the wavelength of 1.55 μm, the extinction ratios are as high as 50.9 dB and 28.2 dB for fundamental transverse magnetic (TM0) and transverse electric (TE0) polarizations, respectively, and the co...

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...

Optical image cloning based on electromagnetic induced absorption.

We investigate, both theoretically and experimentally, optical image cloning via electromagnetic induced absorption (EIA). We demonstrate the transfer of small 2D real images imprinted onto a strong coupling beam to a weak probe beam in a Rb vapor cell. We show through EIA that the coupling beam's image is cloned beyond the usual diffraction, with a potential improvement in spatial resolution of the cloned image by a factor of three in comparison to that of the original coupling beam. Optical cloning throug...

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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