<i>N</i>-Heterocyclic Carbene Catalyzed Highly Chemoselective Intermolecular Crossed Acyloin Condensation of Aromatic Aldehydes with Trifluoroacetaldehyde Ethyl Hemiacetal

Ramanjaneyulu, Bandaru T.; Mahesh, Sriram; Anand, Ramasamy Vijaya

doi:10.1021/ol502581b

Cited by 33 publications

(15 citation statements)

References 75 publications

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“…To clarify this perplexity and gain more insights into this highly selective process, we conducted the control experiments depicted in Scheme . First, despite the well-known reversible feature of benzoin reactions, the exposure of compound 2a to the standard conditions with catalyst ent -E or A did not result in any erosion of the ee value or the formation of aldol products, indicating an irreversible benzoin process in this protocol (Scheme , eqs 1 and 2). However, the treatment of aldol product 2a′ with trichloro-catalyst E led to a full conversion of 2a′ to the benzoin product 2a under the standard conditions, presumably through a retro-aldol-benzoin process (Scheme , eq 3).…”

Section: Mechanistic Studiesmentioning

confidence: 86%

Dynamic Kinetic Resolution Enabled by Intramolecular Benzoin Reaction: Synthetic Applications and Mechanistic Insights

et al. 2016

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The highly enantio-, diastereo-, and regioselective dynamic kinetic resolution of β-ketoesters and 1,3-diketones was achieved via a chiral N-heterocyclic carbene catalyzed intramolecular cross-benzoin reaction. A variety of tetralone derivatives bearing two contiguous stereocenters and multiple functionalities were liberated in moderate to excellent yields and with high levels of stereoselectivity (>95% ee and >20:1 dr in most cases). In addition, the excellent regioselectivity control for aryl/alkyl 1,3-diketones, and the superior electronic differentiation of 1,3-diarylketones were highlighted. Moreover, a set of new mechanistic rationale that differs with the currently widely accepted understanding of intramolecular benzoin reactions was established to demonstrate the superior preference of benzoin over aldol transformation: (1) A coexistence of competitive aldol and benzoin reactions was detected, but a retro-aldol-irreversible benzoin process performs a vital role in the generation of predominant benzoin products. (2) The most essential role of an N-electron-withdrawing substituent in triazolium catalysts was revealed to be accelerating the rate of the benzoin transformation, rather than suppressing the aldol process through reducing the inherent basicity of the catalyst.

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Section: Mechanistic Studiesmentioning

confidence: 86%

Dynamic Kinetic Resolution Enabled by Intramolecular Benzoin Reaction: Synthetic Applications and Mechanistic Insights

et al. 2016

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“…Carbene can act as an organocatalyst was demonstrated long back in 1940s [114]. Since then, several attempts have been undertaken to develop NHC mediated Benzoin, Acyloin condensation reactions [115][116][117][118][119] (Figure 30).…”

Section: Nhc As Organocatalystsmentioning

confidence: 99%

Recent Development of Carbenes: Synthesis, Structure, Photophysical Properties and Applications

Manna¹,

Verma²,

Panja³

et al. 2022

Carbene

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Carbenes are highly reactive intermediates in organic synthesis. These divalent carbon species are generally transient in nature and cannot be isolated. However, they can form stabile metal complexes. Later on, the development of N-heterocyclic carbene (NHC) and other stable carbene led to the application of these carbon (II) donor ligands in the synthesis of complex natural products, transition metal catalysis, organo-catalysis and several other synthetic methodologies. Here in this short review, we will discuss the brief history of the development of carbenes, synthesis of stable carbenes (NHC in particular), and their applications in natural products synthesis transition metal chemistry/organometallics. In addition to synthesis and application, the chapter will consist of a detailed structural analysis of carbenes and exciting photophysics of this class of compounds. Special emphasis will be given to electronic structure. The role of carbene in the development of luminescent NHC transition metal complexes, the tuning of emission properties as well as their active role as photocatalysts in the reduction of CO2 will also be discussed.

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“…The organocatalytic properties of N-heterocyclic carbenes (NHCs) are well documented for a broad range of synthetic transformations, including benzoin-and acylointype reactions [1][2][3][4][5][6][7][8], transesterifications [9][10][11][12][13][14][15][16][17][18][19], and annulations [20][21][22][23][24][25][26][27][28], among many others [29][30][31][32]. For the majority of these synthetic procedures, NHCs are typically generated in situ by the deprotonation of a conjugate acid heterocyclic azolium salt.…”

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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N-Heterocyclic Carbene Catalyzed Highly Chemoselective Intermolecular Crossed Acyloin Condensation of Aromatic Aldehydes with Trifluoroacetaldehyde Ethyl Hemiacetal

Cited by 33 publications

References 75 publications

Dynamic Kinetic Resolution Enabled by Intramolecular Benzoin Reaction: Synthetic Applications and Mechanistic Insights

Dynamic Kinetic Resolution Enabled by Intramolecular Benzoin Reaction: Synthetic Applications and Mechanistic Insights

Recent Development of Carbenes: Synthesis, Structure, Photophysical Properties and Applications

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

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