Aldiminium and 1,2,3-triazolium dithiocarboxylate zwitterions derived from cyclic (alkyl)(amino) and mesoionic carbenes

• Nedra Touj,
• François Mazars,
• Guillermo Zaragoza and
• Lionel Delaude

Beilstein J. Org. Chem. 2023, 19, 1947–1956, doi:10.3762/bjoc.19.145

• analysis. The analytical data recorded for all these adducts were compared with those reported previously for related NHC·CS2 betaines derived from imidazolinium or (benz)imidazolium salts. Due to the absence of electronic communication between the CS2 unit and the orthogonal heterocycle, all the CAAC·CS2

• air and moisture, followed by an aqueous work-up. These results sharply contrasted with those obtained previously with a range of imidazolinium, benzimidazolium, or imidazolium salts, which were successfully converted into NHC·CS2 zwitterions under mild aerobic conditions [75]. Yet, the greater proton

• betaines were determined by X-ray diffraction analysis. The various analytical data recorded for all these compounds were compared with those reported previously for related NHC·CS2 zwitterions derived from imidazolinium or (benz)imidazolium salts. Due to the absence of electronic communication between the

Application of N-heterocyclic carbene–Cu(I) complexes as catalysts in organic synthesis: a review

• Nosheen Beig,
• Varsha Goyal and
• Raj K. Bansal

Beilstein J. Org. Chem. 2023, 19, 1408–1442, doi:10.3762/bjoc.19.102

• –Cu(I) complexes 12 (Scheme 5). A variety of bases, namely metal alkoxides, alkali metal carbonates, n-butyllithium, and lithium bis(trimethylsilyl)amide have been employed for this purpose. In 2010, Diez-González et al. synthesized a variety of NHC–Cu(I) complexes 14 from imidazolium salts 13 using

• enantioselectivity, using NHC–Cu(I) complexes generated in situ from chiral imidazolium salts containing possible chelating functional group(s). For example, the conjugate addition of Grignard reagents to 3-methyl- and 3-ethylcyclohexenones in the presence of the C2-symmetric chiral NHC–copper complex catalyst

Functionalization of imidazole N-oxide: a recent discovery in organic transformations

• Koustav Singha,
• Imran Habib and
• Mossaraf Hossain

Beilstein J. Org. Chem. 2022, 18, 1575–1588, doi:10.3762/bjoc.18.168

• rotation of the isolated products 43a–h did not show any racemization under the standard reaction conditions. Thereafter, imidazolium salts 45a–d, obtained from imidazole N-oxides 44a–d, provided the desired optically active 3-butoxyimidazole-2-thiones 47a–d in 66–83% yield using triethylamine in pyridine

• reactions with elemental sulfur [23][24][25], resulting in the generation of non-enolizable imidazole-2-thiones. At first, the alkylation of 2-unsubstituted imidazole N-oxides 40 took place in the presence of an equimolar quantity of benzyl bromide in CH2Cl2 at rt providing the (N-benzyloxy)imidazolium

• salts 41. The latter underwent deprotonation in the presence of triethylamine in pyridine to generate the carbene intermediates 42 (Scheme 9). After that, the optically active imidazole-2-thiones 43 were obtained through the reaction with elemental sulfur. In CHCl3 solutions, the study of the optical

Functionalization of 4-bromobenzo[c][2,7]naphthyridine via regioselective direct ring metalation. A novel approach to analogues of pyridoacridine alkaloids

• Benedikt C. Melzer,
• Alois Plodek and
• Franz Bracher

Beilstein J. Org. Chem. 2019, 15, 2304–2310, doi:10.3762/bjoc.15.222

• , phenolates), acyl anions (generated by umpolung of aldehydes with imidazolium salts) and by palladium-catalyzed cross-coupling reactions (Suzuki, Stille) [10]. A related Stille cross coupling of a benzo[c][2,7]naphthyridine bearing a triflate group at C-5 gave an intermediate for the total synthesis of

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

Synthesis and selected transformations of 2-unsubstituted 1-(adamantyloxy)imidazole 3-oxides: straightforward access to non-symmetric 1,3-dialkoxyimidazolium salts

• Grzegorz Mlostoń,
• Małgorzata Celeda,
• Katarzyna Urbaniak,
• Marcin Jasiński,
• Vladyslav Bakhonsky,
• Peter R. Schreiner and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2019, 15, 497–505, doi:10.3762/bjoc.15.43

• . Deprotonation of the latter with triethylamine in the presence of elemental sulfur allows the in situ generation of the corresponding imidazol-2-ylidene, which traps elemental sulfur yielding a 1,3-dihydro-2H-imidazole-2-thione as the final product. Keywords: alkoxyamines; imidazole N-oxides; imidazolium salts

• approach to these products comprises the alkylation (in most cases methylation) of 1-hydroxyimidazole N-oxides. However, the products of the monomethylation could not be obtained, but symmetric N,N-disubstituted imidazolium salts resulting from double O-alkylation were isolated [18]. On the other hand

• -tetramethylcyclobutane-1,3-dione. Imidazolium salts are of special importance as they are widely used as ionic liquids or precursors of imidazole-based nucleophilic carbenes (imidazol-2-ylidenes). For example, deprotonation of 1,3-diadamantylimidazolium chloride led to the first stable imidazol-2-ylidene (the so-called

An efficient Pd–NHC catalyst system in situ generated from Na₂PdCl₄ and PEG-functionalized imidazolium salts for Mizoroki–Heck reactions in water

• Nan Sun,
• Meng Chen,
• Liqun Jin,
• Wei Zhao,
• Baoxiang Hu,
• Zhenlu Shen and
• Xinquan Hu

Beilstein J. Org. Chem. 2017, 13, 1735–1744, doi:10.3762/bjoc.13.168

• Nan Sun Meng Chen Liqun Jin Wei Zhao Baoxiang Hu Zhenlu Shen Xinquan Hu College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310032, China 10.3762/bjoc.13.168 Abstract Three PEG-functionalized imidazolium salts L1–L3 were designed and prepared from commercially available

• materials via a simple method. Their corresponding water soluble Pd–NHC catalysts, in situ generated from the imidazolium salts L1–L3 and Na2PdCl4 in water, showed impressive catalytic activity for aqueous Mizoroki–Heck reactions. The kinetic study revealed that the Pd catalyst derived from the imidazolium

• 10,000. Keywords: aqueous homogeneous catalysis; Mizoroki–Heck reaction; Na2PdCl4; PEG-functionalized imidazolium salts; Introduction Nowadays, both increasing environmental concerns and drastic commercial competition are the driving forces to develop more sustainable and economic processes for

Ionic liquids as transesterification catalysts: applications for the synthesis of linear and cyclic organic carbonates

• Maurizio Selva,
• Alvise Perosa,
• Sandro Guidi and
• Lisa Cattelan

Beilstein J. Org. Chem. 2016, 12, 1911–1924, doi:10.3762/bjoc.12.181

• of glycerol trioleate with methanol: both, acidic ionic liquids (e.g., 1-allyl-3-(butyl-4-sulfonyl)imidazolium trifluoromethanesulfonate [BsAIm][OTf]) supported onto sulfhydryl-group-modified SiO2 (MPS-SiO2) [38], and imidazolium salts (e.g., 1-allyl-dodecylimidazolium hydroxide ([ADIm][OH

• oxygenated derivatives, such as sec-butanol, in place of compounds like MTBE (methyl tert-butyl ether) for the formulation of gasoline blends. Tests with the imidazolium salts collected in Scheme 5 have demonstrated that they are not only competitive with conventional acid catalysts, but that they also can

• be recovered and reused to allow quantitative conversions even after several recycles. Moreover, the study highlighted that the catalytic activity increased with increasing acidity of the ILs and particularly with cations bearing SO3H anions (Scheme 5: ILs I, II, III, and IV). The same imidazolium

Experimental and theoretical investigations on the high-electron donor character of pyrido-annelated N-heterocyclic carbenes

• Michael Nonnenmacher,
• Dominik M. Buck and
• Doris Kunz

Beilstein J. Org. Chem. 2016, 12, 1884–1896, doi:10.3762/bjoc.12.178

• (current address of corresponding author) 10.3762/bjoc.12.178 Abstract Rh(CO)2Cl(NHC) complexes of dipyrido-annelated N-heterocyclic carbenes were prepared. From the C–H coupling constant of the respective imidazolium salts and the N–C–N angle of the N-heterocyclic carbene (NHC), a weaker σ-donor

• -donor character (deduced directly from the larger 1JCH coupling constant of the respective imidazolium salts that correlates with the higher s-character in the C–H bond). Therefore, we expected the average CO stretching frequencies to lie about 15 cm−1 higher at around 2050 cm−1 for complexes 2a and 2b

Methylpalladium complexes with pyrimidine-functionalized N-heterocyclic carbene ligands

• Dirk Meyer and
• Thomas Strassner

Beilstein J. Org. Chem. 2016, 12, 1557–1565, doi:10.3762/bjoc.12.150

• reported the synthesis of the imidazolium salts 1–4 and their corresponding silver complexes 5–8. The reaction with dichloro(cyclooctadiene)-palladium(II) [(COD)PdIICl2] allowed for the isolation and characterization of the [((pym)^(NHC-R))PdIICl2]-complexes [34]. For the synthesis of the corresponding

• decompose in DMSO-d6 by reductive cis-elimination [40] leading to imidazolium salts with the methyl group on the former carbene carbon atom and palladium black. The weaker coordination is most probably caused by the stronger trans effect of the methyl group. The decomposition is significantly slower in

• institute using an EuroVektor Euro EA-300 Elemental Analyzer. Chemicals were supplied by Acros, Fluka and Aldrich and used as received; solvents were dried by standard procedures before use. Imidazolium salts 1–4 [34], silver complexes 5–8 [27], chloro(methyl)(cyclooctadiene)palladium(II) [54] and dimethyl

Bi- and trinuclear copper(I) complexes of 1,2,3-triazole-tethered NHC ligands: synthesis, structure, and catalytic properties

• Shaojin Gu,
• Jiehao Du,
• Jingjing Huang,
• Huan Xia,
• Ling Yang,
• Weilin Xu and
• Chunxin Lu

Beilstein J. Org. Chem. 2016, 12, 863–873, doi:10.3762/bjoc.12.85

• Republic of China 10.3762/bjoc.12.85 Abstract A series of copper complexes (3–6) stabilized by 1,2,3-triazole-tethered N-heterocyclic carbene ligands have been prepared via simple reaction of imidazolium salts with copper powder in good yields. The structures of bi- and trinuclear copper complexes were

• , structural characterization, and catalytic properties of a few copper-1,2,3-triazole-tethered NHC complexes is reported. Results and Discussion Synthesis and spectroscopic characterization The imidazolium salts (1a–e) were prepared according to the reported procedure in 61–90% yields [27]. These imidazolium

• salts have been characterized by NMR spectroscopy. The 1H NMR spectra of these imidazolium salts show singlet peaks between 10.04 and 10.89 ppm in DMSO-d6. As seen in Scheme 1, copper–NHC complexes 3–6 can be obtained in 52–90% yields via directly reacting the corresponding imidazolium salts with an

Efficient synthetic protocols for the preparation of common N-heterocyclic carbene precursors

• Morgan Hans,
• Jan Lorkowski,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2015, 11, 2318–2325, doi:10.3762/bjoc.11.252

• common NHC precursors and their synthesis from acyclic starting materials is of utmost practical importance [41]. One of the most atom-economical and straightforward path to elaborate symmetrical imidazolium salts involves the combination of glyoxal, which provides the C4–C5 heterocyclic backbone of the

• interested in the preparation of IMes·HBF4 because imidazolium tetrafluoroborates are usually less hygroscopic and easier to crystallize than chlorides [45]. Moreover, when imidazolium salts are used to generate NHCs in situ, for instance to accomplish organocatalytic transformations, the exact nature of the

• for the azolium chloride building block [43]. From a practical point of view, both procedures represented a significant breakthrough, because the one-pot strategy was largely inefficient for imidazolium salts bearing bulky aromatic substituents on their nitrogen atoms. Over the years, minor changes

Fe(II)/Et₃N-Relay-catalyzed domino reaction of isoxazoles with imidazolium salts in the synthesis of methyl 4-imidazolylpyrrole-2-carboxylates, its ylide and betaine derivatives

• Ekaterina E. Galenko,
• Olesya A. Tomashenko,
• Alexander F. Khlebnikov,
• Mikhail S. Novikov and
• Taras L. Panikorovskii

Beilstein J. Org. Chem. 2015, 11, 1732–1740, doi:10.3762/bjoc.11.189

• performed on Agilent Technologies SuperNova diffractometer at 100 K using monochromated Cu Kα radiation. Thin-layer chromatography (TLC) was conducted on aluminium sheets with 0.2 mm silica gel (fluorescent indicator, Macherey-Nagel). The isoxazoles 7 [37][38] and imidazolium salts 9 [29] were synthesized

A facile synthetic route to benzimidazolium salts bearing bulky aromatic N-substituents

• Gabriele Grieco,
• Olivier Blacque and
• Heinz Berke

Beilstein J. Org. Chem. 2015, 11, 1656–1666, doi:10.3762/bjoc.11.182

• increased in addition the steric congestion [20]. It is important to recognize that synthetically the stable forms for handling of imidazole carbenes are imidazolium salts. In imidazolium-based NHC chemistry two synthetic aspects are important: 1) there are several fundamental synthetic routes available

• are designed to bear bulky aromatic moieties as N1,N2-substituents. As mentioned before the synthetic pre-stages of NHCs are always imidazolium salts, but benzimidazolium salts, which possess two aromatic N1,N2-substituents are rare. More common are benzimidazolium salts having different N1,N2

• of nucleophilic aromatic substitutions (SNAr) of benzene-1,2-diamine at 2-chloropyridine (Scheme 1). Once all the different N1,N2-diarylbenzene-1,2-diamines were prepared a method had to be developed to build up the imidazolium salts by ring closure. 3-Cl and 4-Cl could principally be obtained from

Cyclic phosphonium ionic liquids

• Sharon I. Lall-Ramnarine,
• Joshua A. Mukhlall,
• James F. Wishart,
• Robert R. Engel,
• Alicia R. Romeo,
• Masao Gohdo,
• Sharon Ramati,
• Marc Berman and
• Sophia N. Suarez

Beilstein J. Org. Chem. 2014, 10, 271–275, doi:10.3762/bjoc.10.22

• peculiarities in melting point and viscosity trends of the C-2-methylated imidazolium salts [33], ether-substituted ILs [34], and bis(oxalato)borate salts [35], detailed investigation into those intriguing behaviors led to deeper insights into the dynamical workings of ILs that have had important impacts on the

Chemoenzymatic synthesis and biological evaluation of enantiomerically enriched 1-(β-hydroxypropyl)imidazolium- and triazolium-based ionic liquids

• Paweł Borowiecki,
• Małgorzata Milner-Krawczyk and
• Jan Plenkiewicz

Beilstein J. Org. Chem. 2013, 9, 516–525, doi:10.3762/bjoc.9.56

• compounds exhibited biological activity that was significantly dependent on the alkyl chain length, with considerably high toxicity of the substituents with 10–16 carbon atoms. The imidazolium salts revealed stronger antibacterial activity than their triazolium analogues. Model for the configurational

Imidazolinium and amidinium salts as Lewis acid organocatalysts

• Oksana Sereda,
• Nicole Clemens,
• Tatjana Heckel and
• René Wilhelm

Beilstein J. Org. Chem. 2012, 8, 1798–1803, doi:10.3762/bjoc.8.205

• , either in substoichiometric amounts or as reaction medium due to hydrogen-bond activation of the protons of the imidazolium cation [7][8][9][10] and other variables, such as π-orbital and charge–charge interactions [8][9][10]. Recently, we applied saturated imidazolium salts with an aryl substituent at

Synthesis of some novel hydrazono acyclic nucleoside analogues

• Mohammad N. Soltani Rad,
• Ali Khalafi-Nezhad and
• Somayeh Behrouz

Beilstein J. Org. Chem. 2010, 6, No. 49, doi:10.3762/bjoc.6.49

• that among published methods for N-alkylation of imidazole derivatives [26][27][28][29][30][31][32][33][34], the method developed by Liu et al. [35] was the most appropriate one for N-alkylation of azoles and their derivatives, since in this method the formation of quaternary imidazolium salts is

1-(4-Alkyloxybenzyl)-3-methyl-1H-imidazol-3-ium organic backbone: A versatile smectogenic moiety

• William Dobbs,
• Laurent Douce and
• Benoît Heinrich

Beilstein J. Org. Chem. 2009, 5, No. 62, doi:10.3762/bjoc.5.62

• study of this interesting association led us to elaborate environment-flexible cationic architectures from which mesomorphic properties emerge. Moreover, we have also explored the influence of different anions on the mesomorphic properties. Keywords: crystal liquid; imidazolium salts; ionic liquid

• materials [19] in which the organic modifications afforded to the imidazolium central part and the ions’ environment (e.g. ion assemblies) closely govern their melting points and their use [20]. The present article concerns a synthetic route to imidazolium salts, which have been modified to present

• this study began with the preparation of the bromide imidazolium salts followed by an anionic exchange step. Bromide derivatives 1n of 1-(4-alkyloxybenzyl)-3-methyl-1H-imidazol-3-ium with n = 8, 10, 12, 14, 16 have been synthesized in good yield (>82%) and on the gram scale. These compounds were

A convenient method for preparing rigid-core ionic liquid crystals

• Julien Fouchet,
• Laurent Douce,
• Benoît Heinrich,
• Richard Welter and
• Alain Louati

Beilstein J. Org. Chem. 2009, 5, No. 51, doi:10.3762/bjoc.5.51

• -arylation of imidazole as a means of expanding the aromatic core and obtaining unsymmetrical imidazolium liquid crystals (Scheme 1). We also describe the influence of the counter anion on the mesomorphism, electrochemistry and the UV properties of these imidazolium salts. Results and Discussion Synthesis

Expedient syntheses of the N-heterocyclic carbene precursor imidazolium salts IPr·HCl, IMes·HCl and IXy·HCl

• Lukas Hintermann

Beilstein J. Org. Chem. 2007, 3, No. 22, doi:10.1186/1860-5397-3-22

• pyrophoric organometallic reagents, and they are conveniently stored and used in the form of their air-stable precursors, namely the imidazolium salts IPr·HCl (1,3-bis-{2,6-diisopropylphenyl}imidazolium chloride; 1) or IMes·HCl (1,3-bis-{2,4,6-trimethylphenyl}imidazolium chloride; 2) (Figure 1). At present

• imidazolium salts by condensation of glyoxal, two equivalents of aliphatic or aromatic amine, and an equivalent of paraformaldehyde in the presence of hydrochloric acid was reported by Arduengo in a patent in 1991 (Scheme 1a). [5] It is successful for a range of alkyl- and arylamines, but the original

• and satisfactory purity. Since THF is relatively expensive, we hoped to find another one-component reaction solvent instead, whose polarity would be low enough to precipitate the imidazolium salts in pure form, but also sufficiently high in order to dissolve the liberated water of condensation. Ethyl