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    Wyświetlanie 1-2 z 2
    Tytuł:
    Asymetryczne reakcje pericykliczne katalizowane kompleksami magnezu
    Magnesium-catalyzed asymmetric pericyclic reactions
    Autorzy:
    Czombik, Anna
    Powiązania:
    https://bibliotekanauki.pl/articles/2200433.pdf
    Data publikacji:
    2022
    Wydawca:
    Polskie Towarzystwo Chemiczne
    Tematy:
    chiralność
    kataliza asymetryczna
    reakcja pericykliczna
    kwas Lewisa
    magnez
    chirality
    asymmetric catalysis
    pericyclic reactions
    Lewis acid
    magnesium
    Opis:
    II Group-metals, like magnesium, are one of the most widespread elements in the environment. The abundance of II-group metals in the Earth’s crust is over 108 times greater than the precious metals. For the industrial applications, the important factors are the low costs of production and higher accessibility of their compounds. This puts the spotlight on alkaline-earth metals competing with transition elements as catalysts in organic synthesis. Features of their derivatives, like mild Lewis acidity and strong Brønsted basicity enabled them to catalyze reactions where Lewis-acidactivation of the substrate is essential. In this review the emphasis was put on magnesium-catalyzed pericyclic reactions, which are recognized as one of the most important methods of new carbon-carbon or carbon-heteroatom bonds formation. Using the catalysts based on II-group metal cations and chiral ligands, a highly stereoselective conversion of achiral substrates into enantioenriched products is possible. The Mg-based catalysts have been used in Diels-Alder, ene and 1,3-dipolar additions. Described synthesis methods were characterized by high efficiency (chemical yields and enantiomeric excesses). Where applicable, the relationships between the structure of catalyst/substrates, conditions and efficiency were discussed. Just now there are a few applications, for example in synthesis of alkaloid (–)-manzacidine or antibiotic of algal origin – (–)-malyngolide.
    Źródło:
    Wiadomości Chemiczne; 2022, 76, 9-10; 755--788
    0043-5104
    2300-0295
    Pojawia się w:
    Wiadomości Chemiczne
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Wiązanie wodorowe i inne oddziaływania typu kwas Lewisa-zasada Lewisa
    The hydrogen bond and the other Lewis acid-Lewis base interactions
    Autorzy:
    Grabowski, S. J.
    Powiązania:
    https://bibliotekanauki.pl/articles/171998.pdf
    Data publikacji:
    2011
    Wydawca:
    Polskie Towarzystwo Chemiczne
    Tematy:
    wiązanie wodorowe
    wiązanie halogenowe
    wiązanie wodorkowe
    oddziaływanie kwas Lewisa-zasada Lewisa
    teoria Atomy w Cząsteczkach
    hydrogen bond
    halogen bond
    hydride bond
    Lewis acid-Lewis base interaction
    atoms in molecules theory
    AIM
    Opis:
    Hydrogen bond is analyzed very often since its importance in numerous chemical, physical and biological processes is very well known. It covers the broad range of various interactions; sometimes this is the subject of discussions and polemics if some of them may be classified as hydrogen bonds. This is because there are numerous definitions of hydrogen bond interaction, often they are hardly accepted since they are not univocal. For example one can mention different types of the proton acceptors for hydrogen bonds; one center electronegative atoms, multi-center acceptors such as đ-electrons or even ó-electrons. There are the other interactions which play the key role in various processes and phenomena. All are often named as no-covalent interactions but the other term, Lewis acid–Lewis base interactions seems to be more accurate. One can mention halogen bond, hydride bond or dihydrogen bond. These interactions may be treated as counterparts or competitors of hydrogen bond. The common characteristic for them, including hydrogen bond, is the electron charge transfer from the Lewis base to the Lewis acid. It was found that the amount of this transfer corresponds roughly to the strength of the interaction. In recent years the ó-hole concept was introduced and developed and it was applied to the Lewis base–Lewis acid interactions. According to this concept the atomic centers are characterized by the presence of the regions of positive and negative electrostatic potentials; very often both regions are detected even for atoms which are commonly known as electronegative ones. In such a way halogen atoms, especially if connected by covalent bond with carbon, may act as Lewis acids and also as Lewis bases. In the first case the halogen bond is formed, recently extensively studied. In this review the characteristics of different Lewis base–Lewis acid interactions are given as well as their common features are presented.
    Źródło:
    Wiadomości Chemiczne; 2011, 65, 11-12; 975-1001
    0043-5104
    2300-0295
    Pojawia się w:
    Wiadomości Chemiczne
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-2 z 2

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