Stereochemistry-59

Agami, Claude; Meynier, Franck; Puchot, C.; Guilhem, Jean; Pascard, Claudine

doi:10.1016/s0040-4020(01)91242-6

Cited by 64 publications

(29 citation statements)

References 29 publications

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“…[404] Der Mechanismus dieser Reaktionen wurde experimentell und rechnerisch untersucht. Erste Studien ergaben zwar, dass am C-C-Verknüpfungsschritt zwei Katalysatormoleküle beteiligt sind, [405] später wurde diese Möglichkeit aber zugunsten eines einfachen Enaminmechanismus ausgeschlossen. [406] Diese Ergebnisse sprechen auch für die Bedeutung der Wasserstoffbrücke zwischen der Carbonsäure und dem Aldehyd bei der Festlegung der Produktkonfiguration.…”

Section: Methodsunclassified

Lewis‐Base‐Katalyse in der organischen Synthese

2008

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Das Erbe von Gilbert Newton Lewis (1875–1946) ist im Wörterbuch der chemischen Bindung und Reaktivität allgegenwärtig. Die Bedeutung seines Konzepts der Donor‐Akzeptor‐Bindung kommt in den eponymen Grundbegriffen für Elektronenpaarakzeptoren (Lewis‐Säuren) und ‐donoren (Lewis‐Basen) zum Ausdruck. Lewis erkannte, dass Säuren nicht automatisch Wasserstoff enthalten müssen (Brønsted‐Säuren) und trug so zum Sturz des “modernen Protonenkults” bei. Seine Entdeckung läutete zunächst die Entwicklung von Lewis‐Säuren als Reagentien und Katalysatoren für organische Reaktionen ein, in den letzten Jahren wurde aber offensichtlich, dass für diese Zwecke auch Lewis‐Basen eingesetzt werden können. Bezüglich der Beschleunigung chemischer Reaktionen ergänzen Lewis‐Basen die entsprechenden Lewis‐Säuren nicht nur elektronisch: Tatsächlich können Lewis‐Basen die Elektrophilie wie auch die Nucleophilie der Verbindungen verstärken, an die sie gebunden werden. Diese unterschiedliche Reaktivität resultiert in einer bemerkenswerten Vielfalt Lewis‐Base‐katalysierter Reaktionen.

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Section: Methodsunclassified

Lewis‐Base‐Katalyse in der organischen Synthese

2008

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“…[404] The mechanism of these reactions has been studied extensively by using both experimental and computational methods. Despite early studies that suggested two catalyst molecules were involved in the carbon-carbon bond-forming step, [405] subsequent investigations have ruled out this possibility in favor of a simple enamine mechanism. [406] These results also lend support to the importance of the carboxylic acid/aldehyde hydrogen bond in determining the stereochemistry of the product.…”

Section: Bifunctional Catalysis With Amino Acids: Combined N-p* Lewismentioning

confidence: 99%

Lewis Base Catalysis in Organic Synthesis

2008

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The legacy of Gilbert Newton Lewis (1875-1946) pervades the lexicon of chemical bonding and reactivity. The power of his concept of donor-acceptor bonding is evident in the eponymous foundations of electron-pair acceptors (Lewis acids) and donors (Lewis bases). Lewis recognized that acids are not restricted to those substances that contain hydrogen (Brønsted acids), and helped overthrow the "modern cult of the proton". His discovery ushered in the use of Lewis acids as reagents and catalysts for organic reactions. However, in recent years, the recognition that Lewis bases can also serve in this capacity has grown enormously. Most importantly, it has become increasingly apparent that the behavior of Lewis bases as agents for promoting chemical reactions is not merely as an electronic complement of the cognate Lewis acids: in fact Lewis bases are capable of enhancing both the electrophilic and nucleophilic character of molecules to which they are bound. This diversity of behavior leads to a remarkable versatility for the catalysis of reactions by Lewis bases.

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“…All reagents were purchased from Aldrich or Janssen except for N,N,N′,N′-tetramethylphosphorodiamidic chloride (TMPDCl) which was purchased from Fluka. 2-Methyl-5-(1-methylethenyl)-1,3-cyclohexanedione 27 and compound 6 29,54 have been characterized before.…”

Section: Experimental Section 53mentioning

confidence: 99%

“…29 To a solution of 17.3 g (69.2 mmol) of this mixture in 125 mL of benzene was added 0.81 mL (9.8 mmol) of pyrrolidine. The reaction mixture was heated at reflux and, after 7 and 18 h, two other 0.81 mL portions of pyrrolidine were added.…”

Section: Cis-(()-3488a-tetrahydro-58a-dimethyl-3-(1-methylethenylmentioning

confidence: 99%

Total Synthesis of Neohedycaryol. Its Possible Role in the Biosynthesis of Eudesmane Sesquiterpenes

et al. 1997

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The total synthesis of neohedycaryol (4), the C(9)-C(10) double bond regioisomer of the germacrane sesquiterpene hedycaryol, was accomplished in 10 steps from the known dione 6. A Marshall fragmentation of the intermediate mesylate 14 was used to prepare the trans,trans-cyclodeca-1,6-diene ring present in neohedycaryol. During the synthesis of 14, a pronounced example of throughbond interactions (TBI) was observed. The preferred elongated chair conformation of neohedycaryol was demonstrated spectroscopically and by chemical conversion into R-, -, and γ-eudesmol. These findings indicate that the occurrence of neohedycaryol as a precursor in the biosynthesis of epieudesmanes as proposed in the literature is unlikely. The preference of neohedycaryol for the elongated chair conformation further shows that the compound occupies the meso form. This implies that neohedycaryol may act as a precursor in the biosynthesis of both ent-and usual eudesmanes.

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Stereochemistry-59

Cited by 64 publications

References 29 publications

Lewis‐Base‐Katalyse in der organischen Synthese

Lewis‐Base‐Katalyse in der organischen Synthese

Lewis Base Catalysis in Organic Synthesis

Total Synthesis of Neohedycaryol. Its Possible Role in the Biosynthesis of Eudesmane Sesquiterpenes

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