1,522 research outputs found

    Regioselective Functionalization of [2.2]Paracyclophanes: Recent Synthetic Progress and Perspectives

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    [2.2]Paracyclophane (PCP) is a prevalent scaffold that is widely utilized in asymmetric synthesis, p-stacked polymers, energy materials, and functional parylene coatings that finds broad applications in bioand materials science. In the last few years, [2.2]paracyclophane chemistry has progressed tremendously, enabling the fine-tuning of ist structural and functional properties. This Minireview highlights the most important recent synthetic developments in the selective functionalization of PCP that govern distinct features of planar chirality as well as chiroptical and optoelectronic properties. Special focus is given to the function-inspired design of [2.2]paracyclophane-based pstacked conjugated materials by transition-metal-catalyzed crosscoupling reactions. Current synthetic challenges, limitations, as well as future research directions and new avenues for advancing cyclophane chemistry are also summarized

    MANAGEMENT DECISION MAKING IN MARKETING

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    Miniaturized microreactors enable photochemistry with laser irradiation in flow mode to convert azidobiphenyl into carbazole with high efficiency

    Reactive & Efficient: Organic Azides as Cross-Linkers in Material Sciences

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    The exceptional reactivity of the azide group makes organic azides a highly versatile family of compounds in chemistry and the material sciences. One of the most prominent reactions employing organic azides is the regioselective copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition with alkynes yielding 1,2,3-triazoles. Other named reactions include the Staudinger reduction, the aza-Wittig reaction, and the Curtius rearrangement. The popularity of organic azides in material sciences is mostly based on their propensity to release nitrogen by thermal activation or photolysis. On the one hand, this scission reaction is accompanied with a considerable output of energy, making them interesting as highly energetic materials. On the other hand, it produces highly reactive nitrenes that show extraordinary efficiency in polymer crosslinking, a process used to alter the physical properties of polymers and to boost efficiencies of polymer-based devices such as membrane fuel cells, organic solar cells (OSCs), light-emitting diodes (LEDs), and organic field-effect transistors (OFETs). Thermosets are also suitable application areas. In most cases, organic azides with multiple azide functions are employed which can either be small molecules or oligo- and polymers. This review focuses on nitrene-based applications of multivalent organic azides in the material and life sciences

    An Intramolecular Iodine-Catalyzed C(sp3^{3})−H Oxidation as a Versatile Tool for the Synthesis of Tetrahydrofurans

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    The first iodine-catalyzed cyclization reaction of aliphatic primary and secondary alcohols gives access to tetrahydrofurans through an intramolecular C(sp3^{3})−H activation. The reaction proceeds under mild reactions using either a floodlight lamp or daylight. The formation of ubiquitous occurring tetrahydrofuran patterns has been extensively investigated in the 1960s as it was one of the first examples of a non-directed remote C−H activation. These approaches suffer from the use of toxic transition metals in overstoichiometric amounts. An attractive metal-free solution for transforming carbon-hydrogen bonds into carbon-oxygen bonds lies in applying economically and ecologically favorable iodine reagents. The presented method involves an intertwined catalytic cycle of a radical chain reaction and an iodine(I/III) redox couple by selectively activating a remote C(sp3^{3})−H bond under visible-light irradiation. The reaction proceeds under mild reaction conditions, is operationally simple and tolerates many functional groups giving fast and easy access to different substituted tetrahydrofurans

    Lanthanide conjugates as versatile instruments for therapy and diagnostics

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    Lanthanides have demonstrated outstanding properties in many fields of research including biology and medicinal chemistry. Their unique luminescence and magnetic properties make them the metals of choice for next generation theranostics that efficiently combine the two central pillars of medicine – diagnostics and therapy. Attached to targeting units, lanthanide complexes pave the way for real-time imaging of drug uptake and distribution as well as specific regulation of subcellular processes with few side effects. This enables individualized treatment options for severe diseases characterized by altered cell expression. The highly diverse results achieved as well as insights into the challenges that research in this area has to face in the upcoming years will be summarized in the present review

    Metal‐to‐Metal Distance Modulation by Ligand Design: A Case Study of Structure‐Property Correlation in Planar Chiral Cyclophanyl Metal Complexes

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    Multinuclear metal complexes have seen tremendous progress in synthetic advances, their versatile structural features, and emerging applications. Here, we conceptualize Metal-to-Metal distance modulation in cyclophanyl metal complexes by bridging ligand design employing the co-facially stacked cyclophanyl-derived pseudo-geminal, -ortho, -meta, and -para constitutional isomers grafted with N-, O-, and P- containing chelates that allow the installation of diverse (hetero)metallic moieties in a distance-defined and spatially-oriented relation to one another. Metal-to-Metal distance modulation and innate transannular “through-space” π–π electronic interactions via the co-facially stacked benzene rings in cyclophanyl-derived complexes as well as their specific stereochemical structural features (element of planar chirality) are crucial factors that contribute to the tuning of structure-property relationships, which stand at the very center from the perspective of cooperative effects in catalysis as well as emerging material applications

    Controlling Regioselectivity in Palladium-Catalyzed C-H Activation/Aryl-Aryl Coupling of 4-Phenylamino[2.2]paracyclophane

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    Selective activation/functionalization of C-H bonds has emerged as an atom- and step-economical process at the forefront of modern synthetic chemistry. This work reports palladium-catalyzed exclusivelypara-selective C-H activation/aryl-aryl bond formation with a preference overN-arylation under the Buchwald-Hartwig amination reaction of 4-phenylamino[2.2]paracyclophane. This innovative synthetic strategy allows a facile preparation of [2.2]paracyclophane derivatives featuring disparatepara-substitutions at C-4 and C-7 positions in a highly selective manner, gives access to a series of potential candidates for [2.2]paracyclophane-derived new planar chiral ligands. The unprecedented behavior in reactivity and preferential selectivity of C-C coupling over C-N bond formation via C-H activation is unique to the [2.2]paracyclophane scaffold compared to the non-cyclophane analogue under the same reaction conditions. Selective C-H activation/aryl-aryl bond formation and sequential C-N coupling product formation is evidenced unambiguously by X-ray crystallography.Peer reviewe

    Controlled, Stepwise Syntheses of Oligomers with Modified Quinoxaline Backbones

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    New oligomers based on quinoxaline units were successfully synthesized through multistep reactions using Wittig coupling, affording (E)-(quinoxalin-2-yl)ethene oligomers. Diverse quinoxaline-based phosphonium salts were designed and synthesized, enabling versatility and compatibility regarding the oligomer-building process. The characterization of the oligomers showed excellent stereoisomer specificity, i.e., a fully E-configurated conjugated π-system. The oligomers’ light absorption/emission profiles indicate potential properties for an application in materials science

    NMR Chemical Shift Ranges of Urine Metabolites in Various Organic Solvents

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    Signal stability is essential for reliable multivariate data analysis. Urine samples show strong variance in signal positions due to inter patient differences. Here we study the exchange of the solvent of a defined urine matrix and how it affects signal and integral stability of the urinary metabolites by NMR spectroscopy. The exchange solvents were methanol, acetonitrile, dimethyl sulfoxide, chloroform, acetone, dichloromethane, and dimethyl formamide. Some of these solvents showed promising results with a single batch of urine. To evaluate further differences between urine samples, various acid, base, and salt solutions were added in a defined way mimicking to some extent inter human differences. Corresponding chemical shift changes were monitored

    Towards the synthesis of calotropin and related cardenolides from 3-epiandrosterone: A-ring related modifications

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    Calotropin and related cardiac glycosides isolated from plants such as calotropis gigantea represent an interesting target for biological investigations and are based on a cardiac steroid that is doubly connected to a sugar moiety. This naturally occurring family of cardiac glycosides was not only reported to have similar cardiac properties as the drugs digitoxin and digoxin, but also show cytotoxic activity against several cancer cell lines. Herein, the first synthetic access to these molecules is reported highlighting the required transformations of the A-ring of the steroid when starting from commercially available and inexpensive 3-epiandrosterone. Our strategy is based on a regioselective C–H oxidation of the methyl group at C-17 delivering the 2α,3β-trans-diol moiety at the same time and ensuring its connection to the sugar unit
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