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Wyszukujesz frazę "enolate" wg kryterium: Temat


Wyświetlanie 1-2 z 2
Tytuł:
DFT/PM3 study of the enoyl-CoA hydratase catalyzed reaction
Autorzy:
Pawlak, J.
Bahnson, B.
Anderson, V.
Powiązania:
https://bibliotekanauki.pl/articles/146962.pdf
Data publikacji:
2002
Wydawca:
Instytut Chemii i Techniki Jądrowej
Tematy:
coenzyme-A
density functional theory
enoyl-CoA hydratase
kinetic isotope effect
ONIOM model
stepwise mechanism
thiolester enolate
Opis:
The enoyl-CoA hydratase catalyzed hydration of alfa,beta-unsaturated thiolesters has been modeled by using the crystal structure of 4-(N,N-dimethylamino)cinnamoyl-CoA bound at the active site. The quantum chemical calculation used the ONIOM mixed level procedure to permit the substrate thiolester and water molecule to be modeled using B3LYP/6-31G(d) level of theory and the active site residues modeled at a semiempirical level using the PM3 Hamiltonian. The results permitted the identification of a stable thiolester enolate intermediate, supporting a stepwise reaction mechanism. The calculation also suggests that the same proton removed from the nucleophilic water molecule is transferred to C alfa in the subsequent protonation of the enolate intermediate. This observation reconciles the stepwise mechanism with the previously reported double isotope effect study [3].
Źródło:
Nukleonika; 2002, 47,suppl.1; 33-36
0029-5922
1508-5791
Pojawia się w:
Nukleonika
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Chiralne amidki litu : właściwości i wybrane zastosowania syntetyczne
Chiral lithium amides : properties and selected synthetic applications
Autorzy:
Piwońska, Magdalena
Powiązania:
https://bibliotekanauki.pl/articles/1409982.pdf
Data publikacji:
2021
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
chiralność
synteza stereoselektywna
enolan
indukcja asymetryczna
lit
chirality
stereoselective synthesis
enolate
asymmetric induction
lithium
Opis:
Reactions involving carbonyl groups are one of the most important transformations in organic chemistry. The nucleophilic properties of carbonyl compounds, when they are in the form of enolate ions, offer many possibilities for creating new carbon-carbon bonds in reactions with electrophiles. In the case of cyclic ketones, enolate formation can be stereocontrolled by deprotonation with the use of chiral lithium amides. Stereoselective formation of the chiral lithium enolate determines the stereochemistry of the product of the subsequent reaction with the electrophile. The induction of chirality in the reaction of enolate ions with electrophiles can also be achieved by using metals other than lithium, i.e. magnesium. When other alkali metals are used, an organometallic catalyst containing a chiral ligand must be present in the reaction. The presence of particular structural elements allow distinguishing the chiral lithium amides between eight major classes. Due to the high reactivity of lithium enolates, they are often converted into the silyl enol ether. This is done in two ways: internal quench (in situ reaction with TMSCl) or external quench. Due to aggregation of the chiral lithium amides and, thus, a decrease in asymmetric induction, the addition of LiCl is necessary for reactions run in external quench conditions. Although there are known examples of the use of chiral lithium amides in a catalytic amount in the deprotonation of epoxides, there is only one example of using less than stoichiometric amounts of chiral lithium amides in the deprotonation of ketones. There are many reports in the literature on the use of chiral lithium amides in total syntheses. The chiral lithium amides were used to form chiral enol silyl ether intermediates, e.g. in synthesis of chlortetaine or (+)-ibogamine. They are also used to form chiral lithium enolates which reacts directly with electrophiles, e.g. in synthesis of lasonolide A.
Źródło:
Wiadomości Chemiczne; 2021, 75, 5-6; 771-798
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-2 z 2

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