N-Heterocyclic Carbene Triazolium Salts Containing Brominated Aromatic Motifs: Features and Synthetic Protocol

Raed, Anas Abo; Dhayalan, Vasudevan; Barkai, Shahar; Milo, Anat

doi:10.2533/chimia.2020.878

Cited by 5 publications

(2 citation statements)

References 9 publications

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“…31 Numerous enantioselective catalysis have focused on the development of novel chiral ligands for use in organo-and transition metalcatalyzed asymmetric reactions. [32][33][34][35][36][37][38][39][40][41] Recently, Benjamin List and David MacMillan have clearly demonstrated the significance of organocatalyst in asymmetric synthesis. 41 Given the broad structural diversity of bicyclic nitrogen heterocycles, these recent Nobel Laureates have demonstrated their ability to catalyse a range of chemical transformations.…”

Section: Synopenmentioning

confidence: 99%

Synthesis and Applications of Asymmetric Catalysis Using Chiral Ligands Containing Quinoline Motifs

Dhayalan¹,

Dandela

Devi³

et al. 2022

SynOpen

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In the past decade, asymmetric synthesis of chiral ligands containing quinoline motifs, a family of natural products displaying a broad range of structural diversity and their metal complexes have become the most significant methodology for the generation of enantiomerically pure compounds of biological and pharmaceutical interest. This review provides comprehensive insight on the plethora of nitrogen-based chiral ligands containing quinoline motifs and organocatalysts used in asymmetric synthesis. However, it is circumscribed to the synthesis of quinoline-based chiral ligands and metal complexes, and their applications in asymmetric synthesis as a homogeneous and heterogeneous catalyst.

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Section: Synopenmentioning

confidence: 99%

Synthesis and Applications of Asymmetric Catalysis Using Chiral Ligands Containing Quinoline Motifs

Dhayalan¹,

Dandela

Devi³

et al. 2022

SynOpen

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“…In particular, the bicyclic pyrrolidine-based triazolyl scaffold 3 reported by Knight and Leeper [44] and related triazolium systems with morpholine-and aminoindane-based structures deliver increased yields and selectivities [45][46][47][48][49]. In addition to the fused ring, the choice of an appropriate N-aryl triazolium substituent is also key to reaction efficiency and product selectivity for a given transformation [50][51][52][53][54][55][56][57][58]. For example, the N-pentafluorophenyl catalyst 4 designed by Connon and Zeitler still holds the record, to our knowledge, of being the most efficient and stereoselective catalyst for the asymmetric benzoin reaction [47].…”

Section: Introductionmentioning

confidence: 99%

Triazolium Salt Organocatalysis: Mechanistic Evaluation of Unusual Ortho-Substituent Effects on Deprotonation

et al. 2021

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Organocatalysis by N-heterocyclic carbenes is normally initiated by the deprotonation of precursor azolium ions to form active nucleophilic species. Substituent effects on deprotonation have an impact on catalytic efficiency and provide insight into general catalytic mechanisms by commonly used azolium systems. Using an NMR kinetic method for the analysis of C(3)-H/D exchange, we determined log kex–pD profiles for three ortho-substituted N-aryl triazolium salts, which enables a detailed analysis of ortho-substituent effects on deprotonation. This includes N-5-methoxypyrid-2-yl triazolium salt 7 and di-ortho-methoxy and di-ortho-isopropoxyphenyl triazolium salts 8 and 9, and we acquired additional kinetic data to supplement our previously published analysis of N-pyrid-2-yl triazolium salt 6. For 2-pyridyl triazoliums 6 and 7, novel acid catalysis of C(3)-H/D exchange is observed under acidic conditions. These kinetic data were supplemented by DFT analyses of the conformational preferences of 6 upon N-protonation. A C(3) deprotonation mechanism involving intramolecular general base deprotonation by the pyridyl nitrogen of the N(1)-deuterated dicationic triazolium salt is most consistent with the data. We also report kDO values (protofugalities) for deuteroxide-catalyzed exchange for 6–9. The protofugalities for 8 and 9 are the lowest values to date in the N-aryl triazolium series.

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Mechanistic Evaluation of Benzoin Catalysis Enabled by Triazolium Salt Application in the Preparation of Benzil and Heterocycles

Sharma,

Manikandan,

Dhayalan

et al. 2023

ChemistrySelect

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A library of functionalized pyrrolidine‐based triazolium salts containing a BF4 counterions have been prepared from readily accessible 2‐pyrolidinone via one‐pot reaction protocol. By separating imine‐ether intermediates, a detailed mechanistic pathway has been investigated. Studied mechanistic investigation improved the synthetic process, resulting in higher yields for pyrrolidine‐based triazolium NHC structures and the large‐scale synthesis of chiral NHCs pre‐catalyst with free OH‐group. The presence of a hydroxyl functional group on the NHCs has the potential for further functionalization and for non‐covalent control over catalytic reactions in which the NHCs can serve as organocatalysts or donor ligands for organometallic catalysis. This benzoin catalytic system was investigated by testing different solvents and aldehydes, NHC‐catalysts loading and time variation effects to prepare a broad range of functionalized benzoin compounds with high yields. The highly reactive pyrrolidine‐based triazolium salts (TACF5) showed significant potential application of organocatalysts in benzoin condensation‐oxidation. EDG and EWG substituted α‐hydroxy ketone derivatives were directly converted to corresponding benzil scaffolds from an aldehyde through one‐pot reaction condition with MnO2 acting as an oxidating reagent in open‐air atmosphere. Selective heterocycles, quinoxaline, imidazole and pyrazine precursor were achieved from simple benzil under green conditions.

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N-Heterocyclic Carbene Triazolium Salts Containing Brominated Aromatic Motifs: Features and Synthetic Protocol

Cited by 5 publications

References 9 publications

Synthesis and Applications of Asymmetric Catalysis Using Chiral Ligands Containing Quinoline Motifs

Synthesis and Applications of Asymmetric Catalysis Using Chiral Ligands Containing Quinoline Motifs

Triazolium Salt Organocatalysis: Mechanistic Evaluation of Unusual Ortho-Substituent Effects on Deprotonation

Mechanistic Evaluation of Benzoin Catalysis Enabled by Triazolium Salt Application in the Preparation of Benzil and Heterocycles

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