The Catalytic Asymmetric Knoevenagel Condensation

Lee, Anna; Michrowska, Anna; Sulzer‐Mossé, Sarah; List, Benjamin

doi:10.1002/anie.201006319

Cited by 156 publications

(61 citation statements)

References 47 publications

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“…10 Addition of benzene-1,3,5-tricarboxylic acid (8) improved the enantioselectivity of the product. Racemic a-branched aldehydes can be converted in a dynamic kinetic resolution into the corresponding enantiomerically enriched products with enantiometric ratios of up to 495:5 ( Table 1; Scheme 3).…”

Section: Reaction Systemsmentioning

confidence: 98%

“…23 Aminopropylsilyl-tethered mesoporous silicate such as MCM-41 also catalyzed Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate in toluene solvent. 24 Mesoporous alumina acted as a base catalyst for the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate (10). 25 Fluorapatite, activated by water and benzyltriethylammonium chloride, acted as a new solid catalyst for the Knoevenagel condensation of aldehydes with nitriles without solvent.…”

Section: Solid Reagents and Catalystsmentioning

confidence: 99%

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2.14 Other Condensation Reactions (Knoevenagel, Perkin, Darzens)

Ebitani

2014

Comprehensive Organic Synthesis II

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Section: Reaction Systemsmentioning

confidence: 98%

Section: Solid Reagents and Catalystsmentioning

confidence: 99%

2.14 Other Condensation Reactions (Knoevenagel, Perkin, Darzens)

Ebitani

2014

Comprehensive Organic Synthesis II

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“…KCs can be catalyzed by a variety of chemicals and reagents whereas several Lewis acidic metals have also been successfully utilized. [75][76][77][78][79][80][81][82][83][84][85] Lewis acidic metals based heterogeneous catalysts stand out due to their potential reusability, stability, and ease in product separation. 49,51 However, functional group tolerance and substrate scope has been one of the limiting factors with heterogeneous catalysts and therefore next-generation catalysts are required.…”

Section: Knoevenagel Condensationmentioning

confidence: 99%

“…[32][33][34][35][36][37][38][39][40] In this context, Lewis acidic metal-based coordination networks have displayed noteworthy results by several groups including us. 49,51,[75][76][77][78][79][80][81][82][83][84][85] The catalytic activities of HCNs 3 -6 was investigated by employing several aromatic and heterocyclic aldehydes using malononitrile as an active methylene compound. In order to optimize the reaction conditions; HCN 3 was used as a representative catalyst for the KCs of benzaldehyde with malononitrile.…”

Section: Knoevenagel Condensationmentioning

confidence: 99%

Three-Dimensional Heterometallic Coordination Networks: Syntheses, Crystal Structures, Topologies, and Heterogeneous Catalysis

Srivastava

Aggarwal

Gupta

2015

Crystal Growth & Design

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This work presents the synthesis of {Co 3+ -Zn 2+ } and {Co 3+ -Cd 2+ } heterometallic coordination networks. These networks are originated from two unique Co 3+ -based metalloligands containing appended arylcarboxylic acid groups at the strategically placed positions. Such appended arylcarboxylate groups coordinate the secondary metal ions, Zn 2+ and Cd 2+ , to afford distinct three-dimensional networks. All four networks display orderly arrangement of secondary metal ions and unique network topologies including an unprecedented one. These networks have been shown to act as the heterogeneous and reusable catalysts for the Knoevenagel condensation reactions and cyanation reactions of assorted aldehydes. Cyanation reactions nicely demonstrate the substrate size-exclusion catalysis.

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“…The dynamic kinetic reduction of 3-substituted indoles could be realized, albeit with modest ee values ( Table 2, entries 14 and 15). [20,15] Unfortunately, the 1 g-based catalytic system was not suitable for indoles having a larger 2-alkyl group, and very low enantioselectivity was obtained for 2-nbutylindole ( Table 2, entry 16). …”

mentioning

confidence: 99%

Direct Asymmetric Hydrosilylation of Indoles: Combined Lewis Base and Brønsted Acid Activation

et al. 2011

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In light of their occurrence in a broad spectrum of natural alkaloids and several important pharmaceutically active compounds, [1] such as those outlined in Scheme 1, enantioenriched indolines have triggered increasing attention in both the synthetic and medicinal chemistry communities. [2] While a variety of protocols, including traditional enzymatic or non-enzymatic kinetic resolutions, [3] and organicmolecule-or metal-mediated asymmetric transformations [4] have been described, the direct asymmetric reduction of prochiral indole precursors would be one of the most straightforward ways to make chiral indolines.[5] Thus, a few transition metal/chiral phosphine complexes, including Rh, Ru, and Ir, have been applied by the groups of Kuwano, Feringa, Pfaltz, and others to the asymmetric hydrogenation of indoles, but the methods usually suffer from a limited substrate scope and relatively harsh reaction conditions.[6] A noteworthy breakthrough was made by Zhou, Zhang, and coworkers who reported an elegant palladium-catalyzed enantioselective hydrogenation of unprotected indoles activated by Brønsted acids. [7] In contrast, Rueping et al. presented the chiral Brønsted acid catalyzed transfer hydrogenation of 3H-indoles with Hantzsch dihydropyridine as the hydrogen source.[8] Nevertheless, to the best of our knowledge, there is no successful precedent on the direct asymmetric reduction of 1H-indoles to access chiral indolines under metal-free conditions despite the fantastic progress of organocatalysis over the past decade.[9]Recently we discovered a highly diastereoselective intramolecular direct imino-ene reaction of indoles tethered to an olefinic side chain at C3, in which a Lewis acid promoted enamine-imine isomerization of the indole through C3 protonation was key to its success.[10] We also recognized that, for unprotected indoles, a similar C3 protonation would occur in the presence of suitable Brønsted acids, which would destroy the aromaticity of indoles and result in the formation of electrophilic indolenium ions.[11] We envisioned that the asymmetric reduction of indoles might be realized by utilizing a chiral organocatalytic system that is compatible with a Brønsted acid activation process. Herein we report our endeavors on the first direct enantioselective hydrosilylation of prochiral 1H-indoles by combined Brønsted acid/Lewis base activation (Scheme 2). [12] The initial investigation in the direct hydrosilylation of 2-methylindole (2 a) with excess HSiCl 3 was conducted by employing N,N-dimethylformamide (1 a; DMF) as the Lewis base catalyst at 0 8C. One equivalent of H 2 O was added to react with HSiCl 3 to generate a strong Brønsted acid, HCl. [13] The reaction was quite inspiring, and the desired indoline product 3 a was cleanly obtained in high yield after 24 hours Scheme 1. Representative chiral indoline derivatives.Scheme 2. Proposed direct asymmetric hydrosilylation of indoles through both Lewis base and Brønsted acid activations.

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The Catalytic Asymmetric Knoevenagel Condensation

Cited by 156 publications

References 47 publications

2.14 Other Condensation Reactions (Knoevenagel, Perkin, Darzens)

2.14 Other Condensation Reactions (Knoevenagel, Perkin, Darzens)

Three-Dimensional Heterometallic Coordination Networks: Syntheses, Crystal Structures, Topologies, and Heterogeneous Catalysis

Direct Asymmetric Hydrosilylation of Indoles: Combined Lewis Base and Brønsted Acid Activation

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