Structure of an η<sup>1</sup> Nickel <i>O</i>-Enolate:  Mechanistic Implications in Catalytic Enyne Cyclizations

Amarasinghe, Kande K. D.; Chowdhury, Sanjoy K.; Heeg, and Mary Jane; Montgomery, John

doi:10.1021/om0010013

Cited by 93 publications

(35 citation statements)

References 42 publications

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“…By omitting the organozinc reagent, metallacycle 19 was isolated and fully characterized as the h 1 , O-bound enolate (Scheme 10). [22] Treatment of metallacycle 19 with dimethylzinc affords the same product 20, which may be obtained from the catalytic reaction of an alkynyl enal and dimethyl zinc. This observation in no way proves that catalytic reactions proceed by this mechanism, but the sequence does provide direct precedent for each of the key individual steps of the metallacycle mechanism.…”

Section: Couplings Of Alkenes With Alkynesmentioning

confidence: 97%

Nickel‐Catalyzed Reductive Cyclizations and Couplings

2004

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For over 50 years, nickel catalysis has been applied in cycloaddition processes. Nickel-catalyzed reductive couplings and cyclizations, however, have only recently attracted a high level of interest. This group of new reactions allows a broad range of multicomponent couplings involving two or more pi components with a main-group or transition-metal reagent. These processes allow the assembly of important organic substructures from widely available reaction components. Multiple contiguous stereocenters, polycyclic ring systems, and novel arrays of complex functionality may often be prepared from simple, achiral, acyclic precursors. With three or more reactive functional groups participating in the catalytic processes, many mechanistic questions abound, including the precise timing of bond constructions and the nature of reactive intermediates. This Review is thus aimed at providing a critical evaluation of recent progress in this rapidly developing field.

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Section: Couplings Of Alkenes With Alkynesmentioning

confidence: 97%

Nickel‐Catalyzed Reductive Cyclizations and Couplings

2004

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“…[201] The proposed mechanism (Scheme 41) involves the formation of a metallacycle 530, the existence of which was demonstrated recently by an X-ray structure of a tmeda-Ni complex. [202] A transmetalation step with various organometallic species would produce intermediate 531, which would undergo a reductive elimination to form the desired product. In the presence of triphenylphosphane, a b-hydride elimination would afford alkene 527.…”

Section: Enyne Tandem Reactionsmentioning

confidence: 99%

Cycloisomerization of 1,n‐Enynes: Challenging Metal‐Catalyzed Rearrangements and Mechanistic Insights

Michelet¹,

Toullec²,

Genêt³

2008

Angew Chem Int Ed

937

248

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Metal-catalyzed cycloisomerization reactions of 1,n-enynes have appeared as conceptually and chemically highly attractive processes as they contribute to the highly demanded search for atom economy and allow the discovery of new reactions. Since the pioneering studies with palladium by the research group of Barry Trost in the mid-1980s, several other metals have been identified as excellent catalysts for the rearrangement of enyne skeletons. Moreover, the behavior of 1,n-enynes may be influenced by other functional groups such as alcohols, aldehydes, ethers, alkenes, or alkynes, thus enhancing the molecular complexity of the synthesized products. Apart from the intrinsic rearrangements of 1,n-enynes, several tandem reactions incorporating intramolecular trapping agents or intermolecular partners have been discovered. This Review aims to highlight the main contributions in this field of catalysis and to propose and comment on the mechanistic insights of the recent discoveries.

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“…[200] Bei der Kombination terminale Dreifach-und [201] Der vorgeschlagene Mechanismus (Schema 41) geht von der Bildung eines Metallacyclus 530 aus, dessen Existenz durch die Röntgenstrukturanalyse eines tmeda-Ni-Komplexes belegt ist. [202] Ein Transmetallierungsschritt mit der Organometallspezies würde dann ein Intermediat 531 ergeben, das durch reduktive Eliminierung zum Produkt 526 führen würde. In Gegenwart von Triphenylphosphan lieferte dagegen eine b-Hydrideliminierung das Alken 527.…”

Section: Enin-tandemreaktionenunclassified

Cycloisomerisierungen von 1,n‐Eninen: faszinierende metallkatalysierte Umlagerungen und mechanistische Einblicke

2008

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Metallkatalysierte Cycloisomerisierungen von 1,n‐Eninen haben sich als konzeptionell und chemisch höchst attraktive Reaktionen erwiesen, da sie dem häufig geforderten Streben nach Atomökonomie nachkommen und neuartige Reaktionsverläufe ermöglichen. Seit den bahnbrechenden Arbeiten in der Gruppe von Barry Trost mit Palladium Mitte der 1980er Jahre wurden viele weitere Metalle als hervorragende Katalysatoren für Enin‐Gerüstumlagerungen identifiziert. Zudem kann das Verhalten von 1,n‐Eninen durch funktionelle Gruppen wie Alkohol‐, Aldehyd‐, Ether‐, Alken‐ oder Alkineinheiten beeinflusst werden, wodurch die Komplexität der synthetisierten Verbindungen zunimmt. Neben den eigentlichen 1,n‐Enin‐Umlagerungen wurden mehrere Tandemreaktionen entdeckt, die intramolekulare Abfangreagentien oder intermolekulare Partner einbeziehen. Diese Übersicht will die wichtigsten Beiträge auf diesem Gebiet der Katalyse behandeln und die mechanistischen Erkenntnisse zu den neuesten Entdeckungen darlegen und kommentieren.

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Structure of an η¹ Nickel O-Enolate: Mechanistic Implications in Catalytic Enyne Cyclizations

Abstract: Two metallacycles derived from the oxidative cyclization of nickel(0) with an alkynyl enal have been isolated and fully characterized. The metallacycles obtained possess an η 1 nickel O-enolate motif within the metallacyclic framework.

Cited by 93 publications

References 42 publications

Nickel‐Catalyzed Reductive Cyclizations and Couplings

Nickel‐Catalyzed Reductive Cyclizations and Couplings

Cycloisomerization of 1,n‐Enynes: Challenging Metal‐Catalyzed Rearrangements and Mechanistic Insights

Cycloisomerisierungen von 1,n‐Eninen: faszinierende metallkatalysierte Umlagerungen und mechanistische Einblicke

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Structure of an η1 Nickel O-Enolate: Mechanistic Implications in Catalytic Enyne Cyclizations

Abstract: Two metallacycles derived from the oxidative cyclization of nickel(0) with an alkynyl enal have been isolated and fully characterized. The metallacycles obtained possess an η 1 nickel O-enolate motif within the metallacyclic framework.

Cited by 93 publications

References 42 publications

Nickel‐Catalyzed Reductive Cyclizations and Couplings

Nickel‐Catalyzed Reductive Cyclizations and Couplings

Cycloisomerization of 1,n‐Enynes: Challenging Metal‐Catalyzed Rearrangements and Mechanistic Insights

Cycloisomerisierungen von 1,n‐Eninen: faszinierende metallkatalysierte Umlagerungen und mechanistische Einblicke

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Structure of an η¹ Nickel O-Enolate: Mechanistic Implications in Catalytic Enyne Cyclizations