Organocatalytic Reactions Enabled by N-Heterocyclic Carbenes

Flanigan, Darrin M.; Romanov‐Michailidis, Fedor; White, Nicholas A.; Rovis, Tomislav

doi:10.1021/acs.chemrev.5b00060

Cited by 1,746 publications

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References 418 publications

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“…Further, the synthetic accessibility 13 of NHC ligands allows easy fine-tuning of their steric and electronic properties. Thus metal-NHC compounds show promise for catalytic applications 14 and also in the biological field. 15,16 For similar reasons, NHCs have attracted much attention in the development of novel nanoparticles [17][18][19][20][21][22][23][24][25][26] as it is estimated that the Au-NHC bond strength is about double that of a corresponding Au-thiol bond, 27 and recent reports show that NHC functionalized AuNPs and gold surfaces outperformed their thiol based counterparts with regards to thermal and chemical stability.…”

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Optically active histidin-2-ylidene stabilised gold nanoparticles

et al. 2017

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Optically active histidin-2-ylidene stabilised gold nanoparticles

et al. 2017

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“…• imidazolium cations (as 2a-b, Figure 7) are the least acidic azolium cations (pK a = 22-24 in water and 22 in DMSO), while triazolium (as 2c) and thiazolium ones (as 2d-f) are the most acidic (pK a = 16-19 in water and 14 in DMSO) [4,49]; and • the nucleophilicity of imidazole NHC (as 1a-b, Figure 7) is three orders of magnitude greater than the thiazole based NHC (as 1d-f) [50].…”

Section: The Acidic and Nucleophilic Properties Of Nhch + /Nhc Systemmentioning

confidence: 99%

Advances in the Knowledge of N-Heterocyclic Carbenes Properties. The Backing of the Electrochemical Investigation

2016

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In the last twenty years, N-heterocyclic carbenes (NHCs) have acquired considerable popularity as ligands for transition metals, organocatalysts and in metal-free polymer synthesis. NHCs are generally derived from azolium based salts NHCH+X− by deprotonation or reduction (chemical or electrochemical) of NHCH+. The extensive knowledge of the physicochemical properties of NHCH+/NHC system could help to select the conditions (scaffold of NHC, nature of the counter-ion X−, solvent, etc.) to enhance the catalytic power of NHC in a synthesis. The electrochemical behavior of NHCH+/NHC system, in the absence and in the presence of solvent, was extensively discussed. The cathodic reduction of NHCH+ to NHC and the anodic oxidation of NHC, and the related effect of the scaffold, solvent, and electrodic material were emphasized. The electrochemical investigations allow acquiring further knowledge as regards the stability of NHC, the acidic and nucleophilic properties of NHCH+/NHC system, the reactivity of NHC versus carbon dioxide and the effect of the hydrogen bond on the catalytic efficiency of NHC. The question of the spontaneous or induced formation of NHC from particular ionic liquids was reconsidered via voltammetric analysis. The results suggested by the classical and the electrochemical methodologies were compared and discussed.

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“…The nucleophilic attack of a Breslow Intermediate on the electrophilic imine, a second proton transfer step and subsequent elimination furnish the condensation product, at the same time regenerating the catalyst. The wide choice of chiral azolium salts reported in the literature allows access to the asymmetric version of the reaction, affording enantio-enriched α-amino ketones [17]. In addition to NHCs, bis(amino)-cyclopropenylidenes (BACs) have also been successfully applied as umpolung-promoting species [18].…”

Section: Introductionmentioning

confidence: 99%

An Overview on the N-Heterocyclic Carbene-Catalyzed Aza-Benzoin Condensation Reaction

Albanese

Gaggero

2018

Catalysts

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Abstract:The N-heterocyclic carbene(NHCs)-catalyzed aza-benzoin condensation reaction is an efficient, single step strategy which employs easily available substrates, such as aldehydes and imines, to provide α-amino ketones. The multifunctionality and high reactivity of α-amino ketones makes these structures attractive for medicinal chemistry and as precursors of a variety of amine derivatives. The different electrophilic characteristics of aldehydes and imines ensure a high regioselective reaction. Enantiomerically-enriched α-amino ketones have been synthesized through stereoselective couplings promoted by chiral N-heterocyclic carbenes. One-pot domino procedures, including an aza-benzoin step, allow valuable complex molecules to be accessed.

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Organocatalytic Reactions Enabled by N-Heterocyclic Carbenes

Abstract: Graphical Abstract

Cited by 1,746 publications

References 418 publications

Optically active histidin-2-ylidene stabilised gold nanoparticles

Optically active histidin-2-ylidene stabilised gold nanoparticles

Advances in the Knowledge of N-Heterocyclic Carbenes Properties. The Backing of the Electrochemical Investigation

An Overview on the N-Heterocyclic Carbene-Catalyzed Aza-Benzoin Condensation Reaction

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