Catalytic, Enantioselective, Vinylogous Aldol Reactions

Denmark, Scott E.; Heemstra, John R.; Beutner, Gregory L.

doi:10.1002/anie.200462338

Cited by 444 publications

(152 citation statements)

References 78 publications

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“…The Campagne group was the rst to report catalytic asymmetric versions of the vinylogous aldol reaction using either Ti(O i Pr) 4 /BINOL or the Carreira group's CuF 2 (tol-BINAP) system. 35 Furthermore, a novel synthesis of a,b-unsaturated dlactones from asymmetric VMARs was also developed by this group and resulted in one-step synthesis of natural product goniothalamin (95) (Fig.…”

Section: Enantioselective Processesmentioning

confidence: 99%

“…4b,23 Their concept used chiral bisphosphoramide 59 and SiCl 4 . It takes advantage of the fact that by extending the coordination sphere the hypervalent silicon becomes more Lewis acidic than the initial SiCl 4 and thus leads to catalysis of the chiral Lewis acid. In the following reaction VMAR adduct 211 was achieved, by catalysis with (R,R)-congured 59, in 93% yield and 99% ee.…”

Section: Diastereoselective Transformations Using Silyl Ketene Acetalsmentioning

confidence: 99%

“…As we will discuss below, each substitution pattern requires unique strategies to generate high levels of stereoselectivity. 4 However, we will start this review with a brief overview of existing protocols and concepts used in VMARs, disregarding their applications in total syntheses. …”

Section: Introductionmentioning

confidence: 99%

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The vinylogous Mukaiyama aldol reaction (VMAR) in natural product synthesis

et al. 2014

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The vinylogous Mukaiyama aldol reaction (VMAR) allows efficient access to larger segments for complex natural product synthesis, primarily polyketides, through the construction of vicinal hydroxyl and methyl groups as well as di and tri-substituted double bonds in one single operation. In this review, we will highlight stereoselective protocols that have been used in natural product synthesis and cluster them into the four groups that can be obtained from different silyl ketene acetals or enol ethers. At the beginning, an overview on different stereoselective VMARs is presented; disregarding their applications in total syntheses.

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Section: Enantioselective Processesmentioning

confidence: 99%

Section: Diastereoselective Transformations Using Silyl Ketene Acetalsmentioning

confidence: 99%

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The vinylogous Mukaiyama aldol reaction (VMAR) in natural product synthesis

et al. 2014

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“…[330b] Auch die [333] Diese Reaktionen sind wegen ihres breiten Substratspektrums bezüglich des Nucleophils (Ketenacetale und N,O-Ketenacetale) und des Aldehyds (aromatisch, ungesättigt und aliphatisch) äußerst nützlich. Die hohe Nucleophilie der N,O-Ketenacetale ermöglichte in Gegenwart des Siliciumtetrachlorid-Phosphoramid-Katalysatorsystems eine allgemeine, hoch selektive Addition an aliphatische Aldehyde (Schema 98).…”

Section: Lewis-base-katalysierte Aldolisierung Mit Enoxytrichlorsilanenunclassified

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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“…Unfortunately, even with the tremendous emphasis placed on the development of catalytic enantioselective vinylogous aldol reactions, an efficient syn-selective asymmetric propionate version is still unavailable, as is a version that delivers quaternary centers. [5] Herein, we document the first examples of the enantioselective catalytic 1,2-diboration of 1,3-dienes (Scheme 1). As depicted in Scheme 1, the 1,2-diboration of 1,3-dienes delivers allyl boron reagents (A) that are perfectly configured to participate in highly selective allylation reactions.…”

mentioning

confidence: 99%

Catalytic Enantioselective 1,2‐Diboration of 1,3‐Dienes: Versatile Reagents for Stereoselective Allylation

et al. 2011

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Polyketides are an important class of natural products that often possess potent biological activity and intriguing chemical structures. Among the methods for constructing these ensembles, the stereoselective addition of allyl metal reagents [1] -particularly allyl boron reagents [2] -to prochiral carbonyls holds particular prominence. With Type I allylation reagents, [3] which react through closed transition states, this reaction not only delivers functionality that is strategically positioned for establishing appropriate oxygenation patterns, but its stereochemical predictability allows ready access to acetate, propionate, and isobutyrate synthetic equivalents. A limitation of many allylation reactions, however, is that they deliver products bearing a terminal alkene; if one desires additional substitution or functionality on the olefin, additional synthetic manipulations are often required. [4] In this regard, the vinylogous aldol reaction has proven particularly important as it delivers enoate-derived homoallylic alcohols. Unfortunately, even with the tremendous emphasis placed on the development of catalytic enantioselective vinylogous aldol reactions, an efficient syn-selective asymmetric propionate version is still unavailable, as is a version that delivers quaternary centers.[5] Herein, we document the first examples of the enantioselective catalytic 1,2-diboration of 1,3-dienes (Scheme 1). As depicted in Scheme 1, the 1,2-diboration of 1,3-dienes delivers allyl boron reagents (A) that are perfectly configured to participate in highly selective allylation reactions.[6-8] Importantly, with an appropriate oxidative work-up, these reactions deliver vinylogous aldol equivalents that directly address the above-described synthesis limitations. Also of significant consequence, is that the allyl boron in the allylation product B may be subject to other useful bondforming reactions, [9] which allow for chain-extending polyketide synthesis.To develop the catalytic synthesis strategy in Scheme 1, efforts were first extended toward the development of an enantioselective 1,2-diboration of terminal dienes.[10] A recent study in our laboratory showed that enantioselective 1,4-diboration of trans-1,3-dienes could be accomplished with [Pt(dba) 3 ] and a chiral phosphonite ligand. [11,12] Although evaluation of alternate phosphorous donors revealed ligands that furnished the desired 1,2-diboration, the selectivity was suboptimal. A more reliable strategy for obtaining the 1,2-diboration product was to replace the trans-diene substrate with cis-1,3-dienes. This approach furnished 1,2-diboration products (3:1 to > 20:1 1,2/1,4 selectivity) across a range of substrates and generally occurred with excellent enantioselection. After optimization, the ligand structures and reaction conditions depicted in Scheme 2 were found to be optimal. With respect to polypropionate synthesis, the diboration of cis pentadiene is paramount and this was found to occur in excellent enantioselectivity (95:5 e.r.) and good yield with ligand L2 (...

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Catalytic, Enantioselective, Vinylogous Aldol Reactions

Cited by 444 publications

References 78 publications

The vinylogous Mukaiyama aldol reaction (VMAR) in natural product synthesis

The vinylogous Mukaiyama aldol reaction (VMAR) in natural product synthesis

Lewis‐Base‐Katalyse in der organischen Synthese

Catalytic Enantioselective 1,2‐Diboration of 1,3‐Dienes: Versatile Reagents for Stereoselective Allylation

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