Anion influences on reactivity and NMR spectroscopic features of NHC precursors

Huynh, Han Vinh; Lam, Truc Tien; Luong, Huyen T.T.

doi:10.1039/c8ra05839c

Cited by 45 publications

(53 citation statements)

References 32 publications

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“…It is well established that the chemical shifts of protons in ammonium salts depend on the counterion electron density. This phenomenon is confirmed by the literature data, [62][63][64][65][66][67][68][69][70][71][72][73] in particular by the examples of imidazole [66][67][68][69][70] and pyrrolidinium salts [70][71][72][73] (ionic liquids).…”

Section: Resultssupporting

confidence: 82%

Synthesis of 2‐Aryl‐N‐(EWG‐methyl)‐N‐methylpyrrolidinium Salts as Precursors of Ylides Entering the [1,2] Stevens Rearrangement

et al. 2021

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N-(EWG-CH2 )-N-methyl-2-phenylpyrrolidinium (EWG -electronwithdrawing group) salts were obtained in two different ways. N-(EWG-CH 2 )-2-phenylpyrrolidines were quaternized with iodomethane, dimethylsulfate or methyl trifluoromethanesulfonate forming pyrrolidinium iodides, methylsulfates and triflates. The counterion exchange in the methylsulfates was carried out yielding respective tetrafluoroborates. The second method was based on the quaternization of N-methyl-2-phenylpyrrolidine with methyl α-halogenoacetate or phenacyl bromide. All listed salts were oily and formed in high yields as mixtures of diastereoisomers, with cis or trans isomer predominating, depending on the method applied. The effect of the counterion present in the obtained salts was analyzed. Ylides generated from these salts in different base/solvent systems afforded products of the [1,2] Stevens rearrangement, 2-EWG-1-methyl-3-phenylpiperidines, with the trans isomers predominating, in moderate to good yields. In case of the [1,2] shift, the yields of respective products depended on EWG present in the substrate (methoxycarbonyl, acetyl, dimethylcarbamoyl and benzoyl).

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Section: Resultssupporting

confidence: 82%

Synthesis of 2‐Aryl‐N‐(EWG‐methyl)‐N‐methylpyrrolidinium Salts as Precursors of Ylides Entering the [1,2] Stevens Rearrangement

et al. 2021

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“…In case of ILs, the physical interpretation of Kamlet-Taft α and β as well as Cataláns SA and SB is convincingly supported by various results of independent spectroscopic measurement methods. [24][25][26][27][28][29][30][31] In contrast, the situation for interpretation of Kamlet-Taft π * is still not clear although several attempts were made to substantiate the π * data of ILs obtained by means of independent physicochemical measurement data. 13,15,17,19,32,33 Kobrak argued that π * is a linear function f (V m ) of the molar volume V m .…”

Section: Introductionmentioning

confidence: 99%

The physical significance of the Kamlet–Taftπ* parameter of ionic liquids

Weiß

Schmidt

Thielemann

et al. 2021

Phys. Chem. Chem. Phys.

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“…The distance between H2⋅⋅⋅Cl1 − atoms is 2,58 Å and the angle C2−H2⋅⋅⋅Cl1 − of 144° is in line with previously reported structures of molecules featuring C−H⋅⋅⋅Cl − hydrogen bonds . The enhanced acidity of the iminium proton of 1 a‐Cl in comparison to 1 a‐OTf should be due to presence of such C2−H2⋅⋅⋅Cl1 − hydrogen bond and can also be deduced from the 1 H NMR spectra of these compounds recorded in CDCl 3 , in which the resonances of these C−H protons differ by almost 1 ppm ( δ =10.32 in 1 a‐OTf vs. 11.29 ppm in 1 a‐Cl , see Figure S32) …”

Section: Resultsmentioning

confidence: 99%

Intramolecular Ring‐Expansion Reaction (RER) and Intermolecular Coordination of In Situ Generated Cyclic (Amino)(aryl)carbenes (cAArCs)

Lorkowski

Krahfuß

Kubicki

et al. 2019

Chemistry A European J

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Cyclic (amino)(aryl)carbenes (cAArCs) based on the isoindoline core were successfully generated in situ by α‐elimination of 3‐alkoxyisoindolines at high temperatures or by deprotonation of isoindol‐2‐ium chlorides with sodium or copper(I) acetates at low temperatures. 3‐Alkoxy‐isoindolines 2 a,b‐OR (R=Me, Et, iPr) have been prepared in high yields by the addition of a solution of 2‐aryl‐1,1‐diphenylisoindol‐2‐ium triflate (1 a,b‐OTf; a: aryl=Dipp=2,6‐diisopropylphenyl; b: Mesityl‐, Mes=2,4,6‐trimethylphenyl) to the corresponding alcohol (ROH) with NEt3 at room temperature. Furthermore, the reaction of 2 a,b‐OMe in diethyl ether with a tenfold excess of hydrochloric acid led to the isolation of the isoindol‐2‐ium chlorides 1 a,b‐Cl in high yields. The thermally generated cAArC reacts with sulfur to form the thioamide 3 a. Without any additional trapping reagent, in situ generation of 1,1‐diphenylisoidolin‐3‐ylidenes does not lead to the isolation of these compounds, but to the reaction products of the insertion of the carbene carbon atom into an ortho C−H bond of a phenyl substituent, followed by ring‐expansion reaction; namely, anthracene derivatives 9‐N(H)aryl‐10‐Ph‐C14H8 4 a,b (a: Dipp; b: Mes). These compounds are conveniently synthesized by deprotonation of the isoindol‐2‐ium chlorides with sodium acetate in high yields. Deprotonation of 1 a‐Cl with copper(I) acetate at low temperatures afforded a mixture of 4 a and the corresponding cAArC copper(I) chloride 5 a, and allowed the isolation and structural characterization of the first example of a cAArC copper complex of general formula [(cAArC)CuCl].

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Anion influences on reactivity and NMR spectroscopic features of NHC precursors

Abstract: The influences of 16 different counteranions on hydrogen-bondings, C–H acidities and 1JC2–H coupling constants of azolium salts have been studied.

Cited by 45 publications

References 32 publications

Synthesis of 2‐Aryl‐N‐(EWG‐methyl)‐N‐methylpyrrolidinium Salts as Precursors of Ylides Entering the [1,2] Stevens Rearrangement

Synthesis of 2‐Aryl‐N‐(EWG‐methyl)‐N‐methylpyrrolidinium Salts as Precursors of Ylides Entering the [1,2] Stevens Rearrangement

The physical significance of the Kamlet–Taftπ* parameter of ionic liquids

Intramolecular Ring‐Expansion Reaction (RER) and Intermolecular Coordination of In Situ Generated Cyclic (Amino)(aryl)carbenes (cAArCs)

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