A laterally-fused N-heterocyclic carbene framework from polysubstituted aminoimidazo[5,1-b]oxazol-6-ium salts

• Andrew D. Gillie,
• Matthew G. Wakeling,
• Bethan L. Greene,
• Louise Male and
• Paul W. Davies

Beilstein J. Org. Chem. 2024, 20, 621–627, doi:10.3762/bjoc.20.54

• -diisopropylphenylamine, could not be converted into the desired imidazolium salt (Scheme 1a, path b). Applying a range of conditions, including those successful on other annulated systems, led to unreacted starting material or hydrolysis products after work-up (see Supporting Information File 1) [5][18][19][23][24][25

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

• of charges (Figure 1) [13][14][15][16]. Crabtree and co-workers first reported the abnormal binding of an imidazolium salt to an iridium hydride at the C4 carbon atom instead of C2 in 2001 [17][18]. Since then, many other metal complexes bearing imidazol-4-ylidene ligands (F) have been reported [7

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

• of imidazolium salt 109 (R1 = iBu) resulted in the highest level of stereoinduction for the conjugate addition of EtMgBr to 3-methylcyclohexenone. 2.2.2 Reaction with organoaluminum reagents: Hoveyda and co-workers [60] investigated the NHC–copper-catalyzed asymmetric conjugate addition of alkyl- and

• were accomplished by using 5 mol % of a chiral monodentate NHC–Cu complex derived from the readily available C1-symmetric imidazolium salt 115 and employing commercially available bis(pinacolato)diboron, B2(pin)2. The desired β-borylcarbonyls were obtained in 60–98% yield and >98:2 er. Following a

• similar approach, Sawamura, Ohmiya and co-worker [62] accomplished the enantioselective conjugate addition of alkylboranes to α,β-unsaturated ketones in the presence of NHC–Cu(I) catalyst generated in situ from a chiral imidazolium salt and PhOK. A variety of functional groups are tolerated in the

Asymmetric tandem conjugate addition and reaction with carbocations on acylimidazole Michael acceptors

• Brigita Mudráková,
• Renata Marcia de Figueiredo,
• Jean-Marc Campagne and
• Radovan Šebesta

Beilstein J. Org. Chem. 2023, 19, 881–888, doi:10.3762/bjoc.19.65

• . Results and Discussion For initial experiments, we have selected the conjugate addition of Me2Zn to acylimidazole 1a catalyzed by a chiral NHC ligand derived from imidazolium salt L1. This NHC precursor has been described previously by Gérard, Mauduit, Campagne and co-workers [19]. The ligand L1 is

Mechanochemical solid state synthesis of copper(I)/NHC complexes with K₃PO₄

• Ina Remy-Speckmann,
• Birte M. Zimmermann,
• Mahadeb Gorai,
• Martin Lerch and
• Johannes F. Teichert

Beilstein J. Org. Chem. 2023, 19, 440–447, doi:10.3762/bjoc.19.34

• approach to circumvent these problems. Results and Discussion We therefore examined different approaches to avoid the transmetallation step (4→5) and to establish a protocol for the direct synthesis of 5 in solution from imidazolium salt 3 (Table 1, liquid state approaches) [48]. The use of strong bases

• preparation of copper(I)/NHC complexes [45][47]. All mechanochemical syntheses were carried out in a planetary ball mill and the vessel was loaded in an argon-filled glovebox. Copper(I) chloride, imidazolium salt 3 and the appropriate base were mixed (in a molar ratio of 1.0:1.0:1.5, respectively) and ground

• as a base were discontinued. As a side comment, the addition of no base at all led to the formation of the imidazolinium cuprate ([3][CuClBr]−, Table 1, entry 11) [46]. The direct transition of the “built-in base” approach conditions to mechanochemical synthesis (copper(I) oxide and imidazolium salt

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• products (e.g., 316) yielded nonracemic secondary (e.g., 317) and tertiary alcohols (e.g., 319). The presence of Cu(OTf)2, an imidazolium salt, and NaOMe leads to a chiral NHC–Cu complex, which, in the presence of B2pin2, generates the corresponding B–Cu species followed by its addition to allylic

Architecture and synthesis of P,N-heterocyclic phosphine ligands

• Wisdom A. Munzeiwa,
• Bernard Omondi and
• Vincent O. Nyamori

Beilstein J. Org. Chem. 2020, 16, 362–383, doi:10.3762/bjoc.16.35

• chlorodiphenylphosphine, afforded 1-methyl-4,5-bis(diphenylphosphino)imidazole (85). Finally, N-methylation gave the imidazolium salt derivative 86 in good yield (65%). Preparation of N-heterocyclic phosphines via metal-catalyzed P–C/N bond formation There is limited availability of certain N-containing precursors and

Installation of -SO₂F groups onto primary amides

• Jing Liu,
• Shi-Meng Wang,
• Njud S. Alharbi and
• Hua-Li Qin

Beilstein J. Org. Chem. 2019, 15, 1907–1912, doi:10.3762/bjoc.15.186

• reactions of phenols (or alcohols) with SO2F2 [29] or the fluorosulfuryl imidazolium salt were developed for mild and effective formation of the corresponding fluorosulfates to act as biological probes in chemical proteomics studies (Scheme 1, (1)) [1][30]. On the other hand, the reactions of aliphatic or

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

• typical conditions (CHCl3 solution, rt) using 1-bromoadamantane as an alkylating agent. However, formation of the expected 1,3-bis(adamantyloxy)imidazolium salt was not observed neither in the absence nor in the presence of AgBF4. Based on this observation, 1-bromoadamantane was replaced by adamantan-1-yl

• trifluoroacetate (Scheme 7). Unexpectedly, this test experiment, performed with 7a at room temperature, led after 24 h not to the expected, symmetric 1,3-di(adamantyloxy)imidazolium salt 13h but to the trifluoroacetate of the starting material, i.e., compound 14, formed side by side with adamantan-1-ol. Apparently

• -thiones by trapping of elemental sulfur [26][32]. Treatment of the symmetric imidazolium salt 15 with triethylamine in pyridine solution in the presence of elemental sulfur led to the 1,3-dihydro-2H-imidazole-2-thione 17 isolated in 83% yield (Scheme 8). In the 1H NMR spectrum, two equivalent HC(4) and HC

Enhanced quantum yields by sterically demanding aryl-substituted β-diketonate ancillary ligands

• Rebecca Pittkowski and
• Thomas Strassner

Beilstein J. Org. Chem. 2018, 14, 664–671, doi:10.3762/bjoc.14.54

• synthesized from 3-methyl-1-phenylimidazolium iodide (1) according to a modified literature procedure (Scheme 1) [41][42]. The starting imidazolium salt 1 was prepared from phenylimidazole by addition of methyl iodide as previously described [43]. Complexes 2 and 3 were obtained as yellow solids in isolated

• calculations. Experimental Both complexes were characterized by 1H, 13C, and 195Pt NMR spectroscopy, ESIMS, and elemental analysis. Formation of the carbene complexes was verified by the disappearance of the characteristic NCHN proton signal of the imidazolium salt in the 1H NMR experiment. The syntheses of

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

• activity in Mizoroki–Heck reactions with DMF as solvent [66]. With this regards, we herein report the development of a new poly(ethylene glycol, PEG) and pyridine bi-functionalized imidazolium salt L1 (Figure 1), which was employed as a water soluble NHC ligand precursor for an in situ generated Pd–NHC

• –NHC species, we treated Na2PdCl4, L1 and NaOEt in D2O at 60 °C for 30 min, and then performed NMR analyses. The 1H NMR spectrum clearly showed that the proton signal of the 2-position (9.41 ppm) of the imidazolium salt L1 disappeared. Two downfield signals at 180.9 and 170.9 ppm appeared in the 13C

• counterparts. Moreover, imidazolium salt L1 was conveniently synthesized from commercially available materials. This newly developed protocol provides an efficient, practical and environmental benign method for the construction of various alkene derivatives. Experimental General All chemicals were reagent

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

• summarizes the reaction mechanism proposed for the synthesis of DMC. The same paper described also the results obtained by supporting the imidazolium salt onto a polystyrene resin (PS). This catalytic system proved to be highly stable and no loss of activity was detected after 200 h of reaction performed in

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

• abilities was limited to determining the overall donor character and taking into account the σ-donor character. The latter is dependant on the s-character of the σ-orbital and thus can be obtained directly from the 1JCH coupling constant of the imidazolium salt [37][38][39] (which can be regarded as the H

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

• ), [(tmeda)Pd(CH3)2], an approach which is frequently used to synthesize dimethyl Pd complexes [50][51][52][53]. Deprotonation of the imidazolium salt 3 and subsequent conversion of the free carbene with [(tmeda)Pd(CH3)2] gave the desired dimethylpalladium(II) complex 15 (Scheme 5) in 47% yield. Conclusion

• , 43.24%; H, 3.47%; N, 8.77%; found: C, 42.73%; H, 3.67%; N, 8.38%. Dimethyl(1-(2-pyrimidyl)-3-(2,6-diisopropylphenyl)imidazolin-2-ylidene)palladium(II) (15) 0.18 g (0.6 mmol) of the imidazolium salt 3 and 0.07 g (0.6 mmol) potassium tert-butanolat are suspended in dry THF at −78 °C under an atmosphere of

Artificial Diels–Alderase based on the transmembrane protein FhuA

• Hassan Osseili,
• Daniel F. Sauer,
• Klaus Beckerle,
• Marcus Arlt,
• Tomoki Himiyama,
• Tino Polen,
• Akira Onoda,
• Ulrich Schwaneberg,
• Takashi Hayashi and
• Jun Okuda

Beilstein J. Org. Chem. 2016, 12, 1314–1321, doi:10.3762/bjoc.12.124

• contains a cysteine residue at position 545 for conjugation [31], an NHC ligand containing a maleimide function was prepared (Scheme 1). The imidazolium salt 3 was synthesized by nucleophilic substitution of mesityl imidazol 1 with maleimide derivative 2. These salts were used to generate the Cu(I) NHC

• precipitate was filtered, washed with toluene (3 × 15 mL) and dried under vacuum to afford analytically pure imidazolium salt 1 (2.58 g, 6.40 mmol, 83%) as colorless powder. 1H NMR (400 MHz, CD2Cl2) δ 10.32 (s, 1H, NCHN), 8.07 (s, 1H, CH=CH), 7.28 (s, 1H, CH=CH), 7.05 (s, 2H, aryl CH), 6.73 (s, 2H, CH=CH

• ), 21.4 (p-Me), 18.0 (o-Me); ESIMS (+) m/z (%): calcd for (C19H22N3O2)+, 324.171; found, 324.170 (100). Synthesis and characterization of NHC-Cu(I)I complex 4 The Imidazolium salt 3 (200 mg, 0.495 mmol, 1.00 equiv), K2CO3 (280 mg, 2.02 mmol, 4.00 equiv) and CuI (95 mg, 0.495 mmol, 1.00 equiv) was stirred

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

• excess of copper powder in CH3CN at 50 °C for 5 h. As shown in Scheme 1, reactions of the pyrimidine imidazolium salt 1a with copper powder in acetonitrile afforded a light yellow Cu(II) complex. In complex 2, the carbenic carbon atom was oxidized into carbonyl, which is similar with the reported

• pyrimidyl-imidazole complex [32]. However, a red binuclear Cu(I) complex 3 was obtained in 57% yield when we reacted pyrimidyl benzimidazolium salt 1b with copper powder. Furtherly, we got a yellow Cu(I)–NHC complex 4 in about 70% yield from pyridine imidazolium salt 1c and copper powder (Scheme 1). In

• ): Similarly as described in a previous procedure [27], the imidazolium salt was prepared similarly as for [(HL3)PF6] from (azidomethyl)benzene (160 mg, 1.2 mmol), copper sulfate pentahydrate (12.5 mg, 0.05 mmol), sodium ascorbate (20 mg, 0.1 mmol), and 3-(prop-2-yn-1-yl)-1-(pyridin-2-yl)-1H-benzo[d]imidazol-3

Muraymycin nucleoside-peptide antibiotics: uridine-derived natural products as lead structures for the development of novel antibacterial agents

• Daniel Wiegmann,
• Stefan Koppermann,
• Marius Wirth,
• Giuliana Niro,
• Kristin Leyerer and
• Christian Ducho

Beilstein J. Org. Chem. 2016, 12, 769–795, doi:10.3762/bjoc.12.77

• . Acetylation of the thus formed primary alcohol resulted in compound 38. This was followed by benzyl and Cbz deprotection and the subsequent urea formation with the imidazolium salt 39 to furnish tripeptide 40. After Boc deprotection, the resultant amine was guanidinylated using isothiourea 41. The thus

Recent advances in N-heterocyclic carbene (NHC)-catalysed benzoin reactions

• Rajeev S. Menon,
• Akkattu T. Biju and
• Vijay Nair

Beilstein J. Org. Chem. 2016, 12, 444–461, doi:10.3762/bjoc.12.47

• precatalyst 54 and DBU promoted enantioselective intramolecular cross-benzoin reaction of 55 to afford chromanone 56 in excellent yield and enantioselectivity (Scheme 34). The NHC-precatalyst is conveniently prepared from camphor in 5 steps [51]. NHC generated from the N-tert-butyl-substituted imidazolium

• salt 57 catalysed the intramolecular cross-benzoin reaction of chalcones derived from o-phthalaldehydes. The reaction proceeded rapidly (20 min) at room temperature to afford good yields (75–94%) of naphthalenone-based tertiary alcohols 58 (Scheme 35) [52]. The synthesis of bicyclic tertiary alcohols

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

• -methylphenyl)imidazolium chloride (IDip*·HCl or IPr*·HCl). Keywords: cyclization; experimental procedure; imidazolinium salt; imidazolium salt; microwave heating; Introduction Since Arduengo and co-workers successfully isolated and characterized the first imidazol-2-ylidene derivative in 1991 [1][2], stable

• -workers on the preparation of another bulky imidazolium salt [72], we found that acetonitrile was a much more convenient solvent than dichloromethane to achieve the condensation of Dip*NH2 and glyoxal. Although the reaction was slow and took about a week to reach completion at 60 °C, the desired

Beyond catalyst deactivation: cross-metathesis involving olefins containing N-heteroaromatics

• Kevin Lafaye,
• Cyril Bosset,
• Lionel Nicolas,
• Amandine Guérinot and
• Janine Cossy

Beilstein J. Org. Chem. 2015, 11, 2223–2241, doi:10.3762/bjoc.11.241

• metathesis Formation of pyridinium/imidazolium salt prior to metathesis Most of the examples of RCM involving substrates that possess a pyridine ring relied on the pre-requisite formation of a pyridinium salt. In 2004, Vaquero et al. reported the synthesis of dihydroquinolizium cations through RCM of dienic

Synthesis and structures of ruthenium–NHC complexes and their catalysis in hydrogen transfer reaction

• Chao Chen,
• Chunxin Lu,
• Qing Zheng,
• Shengliang Ni,
• Min Zhang and
• Wanzhi Chen

Beilstein J. Org. Chem. 2015, 11, 1786–1795, doi:10.3762/bjoc.11.194

• (1), [RuL1(CH3CN)4](PF6)2 (2) and [RuL2(CH3CN)3](PF6)2 (3) The ruthenium–NHC complexes 1 and 2 were synthesized by using the corresponding nickel–NHC complexes as the carbene transfer agent [36]. The reaction of imidazolium salt HL1(PF6) (L1 = 3-methyl-1-(pyrimidine-2-yl)imidazolylidene) with Raney

• imidazolium salt HL2(PF6) (L2 = 1,3-bis(pyridin-2-ylmethyl)benzimidazolylidene) with a half equivalent of [Ru(p-cymene)Cl2]2 and an excess of NH4PF6 in a refluxing acetonitrile solution afforded the tri-acetonitrile coordinated Ru(II)–NHC complex [RuL2(CH3CN)3](PF6)2 (3) in a yield of 61% (Scheme 2). The

A new charge-tagged proline-based organocatalyst for mechanistic studies using electrospray mass spectrometry

• J. Alexander Willms,
• Rita Beel,
• Martin L. Schmidt,
• Christian Mundt and
• Marianne Engeser

Beilstein J. Org. Chem. 2014, 10, 2027–2037, doi:10.3762/bjoc.10.211

• now [43][53]. They consist of an imidazolium salt attached to hydroxyproline via an ester group at the end of a flexible alkyl spacer. Interestingly, such charge tags can cause an enhancement of the catalytic performance through electrosteric activation [53], but backfolding can also alter and disturb

Relay cross metathesis reactions of vinylphosphonates

• Raj K. Malla,
• Jeremy N. Ridenour and
• Christopher D. Spilling

Beilstein J. Org. Chem. 2014, 10, 1933–1941, doi:10.3762/bjoc.10.201

• ethylimidazole would reacted with dimethyl methylphosphonate to give ethylimidazolium methylphosphonate in quantitative yield [32]. We were pleased to observe [31P NMR] that dimethyl vinylphosphonate 12b reacted with neat methylimidazole at 100 °C to give the imidazolium salt 37 (Scheme 13). Treatment of the

Synthesis of zearalenone-16-β,D-glucoside and zearalenone-16-sulfate: A tale of protecting resorcylic acid lactones for regiocontrolled conjugation

• Hannes Mikula,
• Julia Weber,
• Dennis Svatunek,
• Philipp Skrinjar,
• Gerhard Adam,
• Rudolf Krska,
• Christian Hametner and
• Johannes Fröhlich

Beilstein J. Org. Chem. 2014, 10, 1129–1134, doi:10.3762/bjoc.10.112

• protection was applied for the synthesis of ZEN-16-sulfate (8) using a procedure that was successfully applied for the synthesis of ZEN-14-sulfate (6) as described recently [20]. Reaction of 22 with the 2,2,2-trichloroethyl (TCE) protected sulfuryl imidazolium salt 23 [36][37] gave the protected sulfate 24

• successfully used as intermediates for the preparation of corresponding glucosides and sulfates applying the Königs–Knorr glucosylation and chemical sulfation using TCE-protected sulfuryl imidazolium salt 23, respectively. These methods were used for the first chemical synthesis of the ZEN-16-conjugates 7 and

• , >99% for 21 and 22; b: 13, Ag2O, MeCN, 96 h, rt; c: TBAF, AcOH, THF, 24 h; d: KOH, THF/H2O, 4 h, rt, 41% for 17, 34% for 7 (3 steps). Chemical sulfation using the 2,2,2-trichloroethyl (TCE)-protected sulfuryl imidazolium salt 23 yielding ZEN-16-sulfate (8) as tetrabutylammonium salt; a: 23, 1,2