A π-Extended Donor-Acceptor-Donor Triphenylene Twin linked via a Pyrazine-bridge

Beta-amino triphenylenes can be accessed via palladium catalyzed amination of the corresponding triflate using benzophe-none imine. Transformation of amine 6 to benzoyl amide 18 is also straightforward and its wide mesophase range demon-strates that the new linkage supports columnar liquid crystal formation. Amine 6 also undergoes clean aerobic oxidation to give a new twinned structure linked through an electron-poor pyrazine ring. The new discotic liquid crystal motif contains donor and acceptor fragments, and is more oval in shape rather than disk-like. It forms a wide range columnar mesophase. Absorption spectra are strong and broad; emission is also broad and occurs with a Stokes shift of ca. 0.7 eV, indicative of charge-transfer characte

Diastereoselektive Synthese von Amino-substituierten Indolizidinen und Chinolizidinen aus Prolinalimin bzw. 2-Piperidincarbaldimin durch intramolekulare Hetero-En-Reaktion

Wir haben uns mit der Frage beschäftigt, inwieweit mit solchen Hetero-En-Reaktionen diastereoselektiv substituierte Indolizidine und Chinolizidine hergestellt werden können, insbesondere im Hinblick darauf, daß eine Reihe dieser Alkaloid-Derivate wirksame Glucosidase-Inhibitoren sind und wegen ihrer Anti-HIV-Aktivitat zunehmendes Interesse gewinnen.Im folgenden berichten wir über eine neue formal intramolekulare Lewis-Säure-katalysierte Imino-En-Reaktion zum diastereoselektiven Aufbau von 7-Alkenyl-8-amino-substituierten Indolizidinen und von 2-Alkyl-1-amino-substituierten Chinolizidinen, bei der sich die relative Konfiguration der beiden neugebildeten Stereozentren durch die Wahl der Lewis-Säure steuern läßt

Intramolecular hetero-Diels-Alder reaction of N-arylimines : applications to the synthesis of octahydroacridine derivatives

A new intramolecular Lewis acid catalyzed hetero-Diels-Alder reaction of N-arylimines 5 with nonactivated olefins tethered to the 2-azadiene system was developed in order to prepare 1,2,3,4,-4a,9,9a,l0-octahydroacridined erivatives 6. Both reactivity and cis/ trans selectivity of 6 were mainly dependent on the substitution pattern in the 3-position of the cyclization precursor 5. The type of Lewis acid plays only a minor role in determination of the cis/trans ratio. The synthetic utility of this new cyclization was increased by performing it as a one-pot reaction. Both absolute configuration and preferred conformation were assigned by detailed NMR studies

A novel B,O,N-doped mesogen with narrowband MR-TADF emission

The St Andrews team would also like to thank EPSRC (EP/P010482/1, EP/W015137/1, EP/W007517/1) for financial support. E.Z.-C. was a Royal Society Leverhulme Trust Senior Research Fellow (SRF\R1\201089).Modification of an unsymmetric B,O,N-doped aromatic core with peripheral mesogenic units triggers self-assembly into a columnar hexagonal mesophase, which is stable between 22 and 144 °C. The columnar assembly is preserved in a glassy state below 22 °C. The B,O,N-doped mesogen displays narrowband sky-blue multiresonance thermally activated delayed fluorescence (MR-TADF) under diluted conditions and bright excimer emission in condensed phase. Our combined experimental and theoretical approach provides insight into the development of strongly aggregating liquid crystalline MR-TADF emitters.Peer reviewe

Novel discotic boroxines : synthesis and mesomorphic properties

Discotic liquid crystals have attracted the attention of many research groups worldwide. Due to the one dimensional charge and ion transport in the columnar mesophase, the ability of liquid crystals (LCs) to self-heal structural defects by thermal annealing and the ease of processing via spin coating, drop casting and other solution processing methods highly useful applications could be realized. Aryl boronic acids are valuable reagents for a number of metal-catalyzed reactions, and boroxines, the cyclic trimers of organoboronic acids, may serve as useful building blocks. However, surprisingly little is known about liquid crystalline boroxines. We described a new synthetic approach to highly substituted triphenylboroxines and investigated their liquid crystalline properties. The tris(3,4,5-trialkyloxy)phenyl functionalized derivatives showed broad mesophases for a minimum alkyl chain length of C9. Textures observed under polarizing optical microscope indicated a columnar hexagonal (Colh) mesophase geometry that was confirmed by X-ray diffraction experiments

Samarium iodide-promoted asymmetric Reformatsky reaction of 3-(2-Haloacyl)-2-oxazolidinones with enals

3-(2-Haloacyl)-2-oxazolidinones were shown to react with enals in an asymmetric SmI2-promoted Reformatsky reaction to give stereochemically well-defined 3-hydroxy-4-alkenyl- and 3-hydroxy-2-methyl-4-alkenyl imides. Chirality transfer of the Evans (S)-oxazolidinone unit via a Zimmerman-Traxler-like transition state resulted in Reformatsky products with a relative syn-configuration. The absolute configuration of compounds obtained is opposite to the corresponding products obtained via aldol addition of boron enolates to enals using the same Evans oxazolidinones

Dissymmetrical U-Shaped π-Stacked Supramolecular Assemblies by Using a Dinuclear CuI Clip with Organophosphorus Ligands and Monotopic Fully π-Conjugated Ligands

International audienceReactions between the U-shape binuclear CuI complex A bearing short metal-metal distances and the cyano-capped monotopic π-conjugated ligands 1-5 carrying gradually bulkier polyaromatic terminal fragments lead to the formation of π-stacked supramolecular assemblies 6-10 respectively in 50-80 % yields. These derivatives have been characterized by multinuclear NMR spectroscopy and X-ray diffraction studies. Their solid state structures show the selective formation of U-shaped supramolecular assemblies in which two monotopic π-conjugated systems present large (6,7,9) or medium (8,10) intramolecular π-overlap revealing π-π interactions. These assemblies self-organize into head-to-tail π-stacked dimers that in turn self-assemble affording infinite columnar π-stacks. The nature, the extentand the complexity of the intermolecular contacts within the head-to-tail π-stacked dimer depends on the nature of the terminal polyaromatic fragment carried by the cyano-capped monotopic ligand but it does not alter the result of the self-assembling process. These results demonstrate that the dinuclear molecular clip A bearing short metal-metal distance allows selective supramolecular assembling processes driven by the formation of intra- and intermolecular short π-π interactions in the resulting self-assembled structures demonstrating that their shape is not only dictated by the symmetry of the building blocks. This approach opens perspectives toward the formation of extented π-stacked columns based on dissymmetrical and functionnal π-conjugated systems

Das Zeitschriften-Paradoxon oder: Wer verfügt über wissenschaftliche Information?

Inhalt: Stephan, Werner: Begrüßung und Einführung - Graf, Bernhard: Zeitschriftenevaluation an der Universität Stuttgart. Ist die inhaltliche Bewertung ein hinreichendes Kriterium für Zeitschriftenabbestellungen? Ein Werkstattbericht - Kirchgässner, Adalbert: 13 Jahre Zeitschriftenabbestellungen an der Universität Konstanz. Die Auswirkungen der Preissteigerungen bei stagnierenden Etats auf das Zeitschriftenportfolio. Veränderungen des Nutzerverhaltens und Konsequenzen für die künftige Bestandspolitik (in einem einschichten System) - Laschat, Sabine: Braucht die Wissenschaft noch Zeitschriften? - Schüz, Wolfram: Das Zeitschriftenparadoxo

Intramolecular borylation via sequential B-Mes bond cleavage for the divergent synthesis of B,N,B-doped benzo[4]helicenes

Authors thank the Natural Sciences and Engineering Research Council of Canada and the Leverhulme Trust (RPG-2016-47) for financial support. J. A. Knöller thanks the Baden Württemberg Stiftung for a scholarship as well as Queen's and Stuttgart University for enabling this research through the Dual Degree Masters program.New symmetric and unsymmetric B,N,B-doped benzo[4]helicenes 3 - 6a/b have been achieved in good yields, using a three-step process, starting from N(tolyl)3 in a highly divergent manner (7 examples). A borinic acid functionalized 1,4-B,N- anthracene 1 was found to display unprecedented reactivity, acting as a convenient and highly effective precursor for selective formation of bromo substituted B,N,B-benzo[4]helicenes 2a/2b via intramolecular borylation and sequential B-Mes bond cleavage in presence of BBr3. Subsequent reaction of 2a/2b with Ar-Li provided a highly effective toolbox for the preparation of symmetrically/unsymmetrically functionalized B,N,B-helicenes. Their high photoluminescence quantum yields along with the small ∆EST suggest the potential as thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs).PostprintPeer reviewe