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  • 1
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 623-625 
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The thermal rearrangement of an N-substituted vinylaziridine to the corresponding (Z)-allylic imine, i.e. a homodienyl-[1,5]-hydrogen shift, was studied at different temperatures in the range 40-90 °C. 1H NMR spectroscopy was used to follow the reaction. Rate constants and activation parameters were determined in solvents that differ in polarity, namely 1,4-dimethylbenzene, 1,2-dichlorobenzene and dimethylformamide (DMF). The activation enthalpies and entropies obtained clearly indicate that the solvent polarity has little influence on the rearrangement, since these values are almost the same in the three solvents used. The low ΔH≠ values (89, 84 and 91 kJ mol-1, respectively) are consistent with a concerted mechanism, while the activation entropies are all small and negative, which is also supportive of a cyclic transition state. The rate constant is slightly higher in the most polar of the solvents used, DMF.
    Additional Material: 2 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Advanced Materials 1 (1989), S. 151-156 
    ISSN: 0935-9648
    Keywords: Process Development ; High Performance Fibers ; High Impact Composites ; Rigid-Rod Polymers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Limited space permits description of only two examples of Kevlar applications research. There are numerous others. In the early product development there were some indications that Kevlar would go mainly into tire reinforcement. This has turned out not to be true. In the mid-seventies Kevlar was participating in only ten market segments and less than fifty specific applications, but today, it is in more than twenty market segments, serving more than two hundred applications, and continued growth is anticipated. Kevlar is produced in a 45 million pound plant in Richmond, VA, USA. In 1988, a second plant was started up in Northern Ireland and plans for a third plant in Japan were announced. The Kevlar innovation story exemplifies the kind of obstacles, interdisciplinary skills and systems approach involved in bringing a laboratory discovery to commercial reality. The story is still unfolding and applications currently not envisioned will undoubtedly become important in the future. .
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0947-6539
    Keywords: asymmetric catalysis ; aziridines ; chiral ligands ; palladium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral palladium π-allyl intermediate for the catalytic asymmetric synthesis shown in Scheme 1 has been isolated as the PF-6 salt. MM 2 calculations have been performed and the structure of the palladium complex in solution has also been investigated by means of NMR spectroscopy. Both the computational and spectroscopic results suggest that in the complex the bidentate bis(aziridine) ligand adopts a conformation that forces the π-allyl moiety out of the normally preferred square-planar geometry. This nicely explains the very high enantioselectivity observed in the title reaction.
    Additional Material: 5 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 101 (1989), S. 665-670 
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 106 (1994), S. 625-646 
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Die Herstellung enantiomerenreiner Verbindungen nimmt innerhalb der Organischen Chemie einen weiten Raum ein. Besonderes Augenmerk liegt dabei auf der Nutzung natürlich vorkommender Ausgangsmaterialien und auf der Entwicklung von Methoden zur enantioselektiven Umsetzung achiraler Substrate. Chirale Aziridine sind in diesem Zusammenhang eine attraktive Verbindungsklasse, da sie über eine Vielzahl von Verfahren enantiomerenrein oder in hohen Enantiomerenüberschüssen verfügbar sind und zudem auf verschiedenste Weise in der asymmetrischen Synthese genutzt werden können. Die Chemie der Aziridine wird durch ringöffnende Reaktionen bestimmt, deren Triebkraft in der Aufhebung von Ringspannung liegt. Durch geeignete Wahl der Substituenten an Stickstoff- und Kohlenstoffatomen gelingt es, in ringöffnenden Reaktionen mit unterschiedlichsten Nucleophilen einschließlich metallorganischen Verbindungen exzellente Stereo- und Regiokontrolle zu erzielen. Dadurch werden chirale Aziridine zu wertvollen Substraten für die Synthese wichtiger biologisch aktiver Vebindungen, z.B. Alkaloiden, Aminosäuren und β-Lactam-Antibiotika, Diastereoselektive Synthesen unter Substratkontrolle sind möglich, wenn Aziridine als abspaltbare chirale Auxiliare eingesetzt werden. Nach Metallierung am Ringkohlenstoffatom können Aziridine auch als chirale Reagentien in der asymmetrischen Synthese benutzt werden. Da chirale Bisaziridine auch als Liganden für Übergangsmetalle wirken können, rükken Anwendungen in dem herausfordernden Gebiet der enantioselektiven Katalyse ins Blickfeld.Der Ausschluß dreigliedriger Carbo-und Heterocyclen aus dem Werkzeugkasten des organischen Chemikers erscheint heutzutage unvorstellbar[1].
    Additional Material: 6 Tab.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 649-654 
    ISSN: 0570-0833
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 9 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 27 (1989), S. 863-871 
    ISSN: 0749-1581
    Keywords: COSY ; One-bond CH correlation ; NOESY ; COLOC-S ; Selective INEPT ; Long-range CH correlation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: After correlation of the majority of signals by COSY and one-bond heteronuclear correlation, the complete assignment of the 1H and 13C NMR spectra of the macrolide antibiotic venturicidin A required the application of long-range CH coupling information. This was accessible by the COLOC-S and selective INEPT experiments, and the sensitivity of these experiments is discussed. Steric information was obtained from a NOESY spectrum, and the solution structure compared with that in the crystal.
    Additional Material: 6 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 33 (1994), S. 599-619 
    ISSN: 0570-0833
    Keywords: Nitrogen heterocycles ; Asymmetric synthesis ; Aziridines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of enantiomerically pure compounds is one of the major areas of organic chemistry. Much emphasis is placed on the elaboration of naturally occurring starting materials and on the development of techniques for enantio-selective transformations of achiral substrates. In this field, chiral aziridines form an attractive class of compounds, since they are available in enantiomerically pure (or highly enriched) form by a variety of procedures and can be used for asymmetric synthesis in a number of different ways. The chemistry of aziridines is dominated by ring-opening reactions, the driving force for which is relief of ring strain. By suitable choice of sub-stituents on the carbon and nitrogen atoms, excellent stereo- and regiocontrol can be attained in ring-opening reactions with a wide variety of nucleophiles, including organometallic reagents; this makes chiral aziridines useful as substrates for the synthesis of important biologically active species including alkaloids, amino acids, and /Mactam antibiotics. Substrate-controlled diastereo-selective synthesis is also possible by use of aziridines as removable chiral auxiliaries, while metalation at a ring carbon atom allows aziridines to be used as chiral reagents for asymmetric synthesis. Chiral bisaziridines can act as ligands for transition metals, and applications in the challenging field of enantioselective catalysis can be envisioned. Today, the exclusion of three-membered carbo- and heterocycles from the arsenal of the organic chemist is inconceivable.H. Heimgartner, Angew. Chem. 1991, 103, 271; Angew. Chem. Int. Ed. Engl. 1991, 30, 238.
    Additional Material: 6 Tab.
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