Carbene-catalyzed enantioselective oxidative coupling of enals and di(hetero)arylmethanes

Qiao, Chunming; Zhu, Tingshun; Majhi, Pankaj Kumar; Mou, Chengli; Chai, Huifang; Zhang, Jingjie; Zhuo, Shitian; Robin, Yonggui

doi:10.1039/c8sc03480j

Cited by 23 publications

(8 citation statements)

References 55 publications

(30 reference statements)

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“…This catalytically generated intermediate can be formed from NHCs upon addition to various α,β-unsaturated aldehydes or acid derivatives (Scheme ). The interception of this intermediate with various bisnucleophiles result in the formation of five- to seven-membered cyclic compounds via [3 + 2], [3 + 3], and [3 + 4] annulations . In the majority of the cases, the carbon-centered nucleophiles add to the β-position of this intermediate in a Michael fashion, followed by the cyclization, to afford the desired products.…”

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“…Based on the literature reports, and the mechanism of the related [3 + 3] annulations catalyzed by NHCs, a tentative mechanism of the reaction is proposed (Scheme ). The initially formed carbene from the chiral triazolium salt undergoes nucleophilic attack on 2-bromoenal, followed by a rapid proton transfer results in the formation of the nucleophilic Breslow intermediate ( I ). , The elimination of bromide from intermediate I generates the key α,β-unsaturated acylazolium intermediate ( II ).…”

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NHC-Catalyzed [3 + 3] Annulation of Thioamides and Modified Enals for the Enantioselective Synthesis of Functionalized Thiazinones

2019

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Unless otherwise specified, all reactions were carried out under an atmosphere of argon in flame-dried reaction vessels with Teflon screw caps. Mesitylene was purchased from commercial sources and stored under argon over 4 Å molecular sieves. The 2-bromoenals were synthesized from the corresponding -unsaturated aldehydes following the literature procedure. 1 All the thioamide derivatives were prepared following the literature procedure. 2 The triazolium salt C was synthesized following the literature procedure. 3 K2CO3 was purchased from SD-Fine. Analytical thin layer chromatography was performed on TLC Silica gel 60 F254. Visualization was accomplished with short wave UV light or KMnO4 staining solutions followed by heating. Flash chromatography was performed on silica gel (230-400 mesh) by standard techniques eluting with Pet. Ether-EtOAc solvent system. All compounds were fully characterized. 1 H and 13 C NMR spectra were recorded on Bruker AV 400 and Bruker Ultra shield spectrometer in solvents as indicated. Chemical shifts (δ) are given in ppm. The residual solvent signals were used as references and the chemical shifts converted to the TMS scale (CDCl3: δH = 7.26 ppm, δC = 77.16 ppm). Infrared (FT-IR) spectra were recorded on a Perkin Elmer Spectrum BX spectrophotometer, ν-max in cm-1. Optical rotations were measured on JASCO P-2000 polarimeter at room temperature using 50 mm cell of 1 mL capacity. HRMS (ESI) data were recorded on a Micromass Q-TOF Micro instrument. HPLC analysis was performed on Agilent Technologies 1260 Infinity II with UV detector.

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NHC-Catalyzed [3 + 3] Annulation of Thioamides and Modified Enals for the Enantioselective Synthesis of Functionalized Thiazinones

2019

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“…Applying the oxidative NHC catalysis strategy, enantioselective synthesis of benzimidazole fused lactams 77 was achieved by oxidative coupling of enals 75 with di(hetero)arylmethanes 76 (Scheme 20). [46] They postulated that the product formation was achieved by two concurrent reaction pathways. The first pathway was through the formation of well‐established α , β ‐unsaturated azolium ester intermediate 78 under oxidative NHC catalysis.…”

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Recent Advances in N‐Heterocyclic Carbene Catalyzed Oxidative Cyclization for the Formation of Heterocycles

2021

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Oxidative N‐heterocyclic carbene catalyst mediated cyclization proved to be an efficient strategy for the construction of various N‐ and O‐ heterocycles. Among several metal‐free methods available for the construction of heterocyclic compounds, oxidative NHC catalysis proved to be an elegant and efficient strategy as several enantioenriched compounds with excellent enantioselectivities can be synthesized in good yields. The most common method of the generation of these heterocycles proceeds via the commonly encountered intermediate in oxidative NHC catalysis (i. e.) acyl azolium intermediate. This intermediate proves to be the active species as it can undergo reaction with suitable substrates leading to the formation of numerous N‐ and O‐ heterocycles. Herein, recent reports on different strategies that enable formal [2+2], [3+2], [3+3], [4+2] or [4+3] annulations between the incoming substrates and acyl azolium species or other active intermediates which can add to suitable substrate leading to various heterocycles were summarized.

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“…More importantly, in this reaction, not only carbon-heteroatom bonds were generated but also a novel carbon-carbon bond was formed ( Figure 16). In 2018, Chi et al reported the enantioselective NHC-catalyzed oxidative coupling of enals and di(hetero)arylmethanes ( Figure 17) [65]. In one of the proposed mechanisms, there occurs a Claisen rearrangement or 1,4-addition, between the generated acylazolium and di(hetero)arylmethane derivative.…”

Section: Oxidative Nhc Catalysismentioning

confidence: 99%

N-Heterocyclic Carbene Catalysis under Oxidizing Conditions

Dzieszkowski

Rafiński

2018

Catalysts

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N-heterocyclic carbene organocatalysis under oxidizing conditions provides a vast range of various synthetic procedures via diverse mechanisms. The available catalysts, bases, oxidants, and oxidizing methods afford numerous opportunities for developing this branch of organocatalysis. Furthermore, implementation of tandem reactions and cooperative catalysis in the described methodology significantly expands the possibilities of modern organic chemistry. This approach allows the synthesis of different structurally complex and often enantiomerically enriched substances, which can be interesting in terms of biological activity and natural product synthesis. Many esters, amides, thioesters, lactams, lactones, and other cyclic compounds obtained in oxidative or oxygenative reactions promoted by N-heterocyclic carbenes can be interesting precursors in advanced organic synthesis. Sophistication and broad applicability prove that the described synthetic approaches are exceptionally worthy of further development.

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Carbene-catalyzed enantioselective oxidative coupling of enals and di(hetero)arylmethanes

Abstract: An N-heterocyclic carbene-catalyzed direct oxidative coupling of enals and di(hetero)arylmethanes allows for quick access to optical pure benzimidazole-fused lactams.

Cited by 23 publications

References 55 publications

NHC-Catalyzed [3 + 3] Annulation of Thioamides and Modified Enals for the Enantioselective Synthesis of Functionalized Thiazinones

NHC-Catalyzed [3 + 3] Annulation of Thioamides and Modified Enals for the Enantioselective Synthesis of Functionalized Thiazinones

Recent Advances in N‐Heterocyclic Carbene Catalyzed Oxidative Cyclization for the Formation of Heterocycles

N-Heterocyclic Carbene Catalysis under Oxidizing Conditions

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