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

• -step ynamide annulation and imidazolium ring-formation sequence. Metalation with Au(I), Cu(I) and Ir(I) at the C2 position provides an L-shaped NHC ligand scaffold that has been validated in gold-catalysed alkyne hydration and arylative cyclisation reactions. Keywords: annulation; carbene; gold

• ; imidazolium; NHC; Introduction Imidazolium-derived nucleophilic heterocyclic carbenes (NHCs) have had a sustained impact across the fields of organometallic and main group chemistry, transition-metal catalysis, materials synthesis and organocatalysis [1]. Laterally annellated polycyclic NHCs offer a useful

• sphere, accessing more diverse fused imidazolium frameworks and different peripheral functionality offers significant scope to influence catalytic properties. Few studies into L-shaped imidazolylidines have explored core motifs beyond ImPy, with NHCs derived from two π-rich rings fused together

Green and sustainable approaches for the Friedel–Crafts reaction between aldehydes and indoles

• Periklis X. Kolagkis,
• Eirini M. Galathri and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2024, 20, 379–426, doi:10.3762/bjoc.20.36

1-Butyl-3-methylimidazolium tetrafluoroborate as suitable solvent for BF₃: the case of alkyne hydration. Chemistry vs electrochemistry

• Marta David,
• Elisa Galli,
• Richard C. D. Brown,
• Marta Feroci,
• Fabrizio Vetica and
• Martina Bortolami

Beilstein J. Org. Chem. 2023, 19, 1966–1981, doi:10.3762/bjoc.19.147

• the hydration of alkynes, named poly(ionic liquid)s (PILs), using trifluoroethanol as solvent [88][89]. One of the most studied classes of ILs in organic chemistry are 1,3-disubstitued imidazolium cations, which are cheap, liquid over a wide range of temperatures, and possess good solvating properties

• [90][91]. Due to their wide electrochemical window, imidazolium ILs are commonly used in organic electrochemistry, simultaneously as solvents and supporting electrolytes [92][93][94]. In addition, the cathodic reduction (both in batch [95] and in flow [96]) can be exploited for the generation of N

• reaction product. All the ILs were dried under vacuum for 16 h, prior to use. Considering the imidazolium tetrafluoroborate ILs, with the exception of BMIm-BF4, a progressive decrease in the yield of 2a, from 76% to 31%, was observed by increasing the length of the aliphatic chain linked to the imidazolic

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

• 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

• . All these adducts were fully characterized by using various analytical techniques and their structural properties compared to those displayed by known, related imidazolinium and (benz)imidazolium-2-dithiocarboxylate betaines. Results and Discussion Currently, the most general strategy to prepare

Benzoimidazolium-derived dimeric and hydride n-dopants for organic electron-transport materials: impact of substitution on structures, electrochemistry, and reactivity

• Swagat K. Mohapatra,
• Khaled Al Kurdi,
• Samik Jhulki,
• Georgii Bogdanov,
• John Bacsa,
• Maxwell Conte,
• Tatiana V. Timofeeva,
• Seth R. Marder and
• Stephen Barlow

Beilstein J. Org. Chem. 2023, 19, 1651–1663, doi:10.3762/bjoc.19.121

• for organic electron-transport materials. Salts of 2-(4-(dimethylamino)phenyl)-4,7-dimethoxy-, 2-cyclohexyl-4,7-dimethoxy-, and 2-(5-(dimethylamino)thiophen-2-yl)benzo[d]imidazolium (1g–i+, respectively) have been synthesized and reduced with NaBH4 to 1gH, 1hH, and 1iH, and with Na:Hg to 1g2 and 1h2

• . Their electrochemistry and reactivity were compared to those derived from 2-(4-(dimethylamino)phenyl)- (1b+) and 2-cyclohexylbenzo[d]imidazolium (1e+) salts. E(1+/1•) values for 2-aryl species are less reducing than for 2-alkyl analogues, i.e., the radicals are stabilized more by aryl groups than the

• and 1,3-dimethyl substituents in pseudo-equatorial positions and the reactive hydridic 2-H-atom pesudo-axial. The cation structures (Figure 5) give some insight into the variety of dopant-ion shapes and sizes that can be afforded by these types of dopants. The angle between the imidazolium ring and

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

• ,b from the reaction of chiral NHC precursors based on a phenoxyimine-imidazolium motif with Cu2O in THF in >90% yield. The reaction solvent was found to be important; in dichloromethane, interactable products were formed in contrast to the excellent yields obtained in THF. Furthermore, the NHC–CuBr

• complex 57 was obtained through reduction of the phenoxyimine-imidazolium bromide 55a (R = t-Bu) with NaBH4 followed by successive alkylation with iPrBr and reaction with Cu2O (Scheme 19) [32]. The use of the synthesized complexes 56a and 57 as precatalysts for the 1,4-conjugate addition to enones and the

Synthesis of ether lipids: natural compounds and analogues

• Marco Antônio G. B. Gomes,
• Alicia Bauduin,
• Chloé Le Roux,
• Romain Fouinneteau,
• Wilfried Berthe,
• Mathieu Berchel,
• Hélène Couthon and
• Paul-Alain Jaffrès

Beilstein J. Org. Chem. 2023, 19, 1299–1369, doi:10.3762/bjoc.19.96

Enabling artificial photosynthesis systems with molecular recycling: A review of photo- and electrochemical methods for regenerating organic sacrificial electron donors

• Grace A. Lowe

Beilstein J. Org. Chem. 2023, 19, 1198–1215, doi:10.3762/bjoc.19.88

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

Friedel–Crafts acylation of benzene derivatives in tunable aryl alkyl ionic liquids (TAAILs)

• Swantje Lerch,
• Stefan Fritsch and
• Thomas Strassner

Beilstein J. Org. Chem. 2023, 19, 212–216, doi:10.3762/bjoc.19.20

• cost-efficient metal salts in a water and air stable ionic liquid is still hard to find [50][51]. In this contribution, we present the use of imidazolium-based tunable aryl alkyl ionic liquids (TAAILs) in a catalytic Friedel–Crafts acylation. This relatively new class of ionic liquids [52] previously

• , does not undergo acylation during the catalysis. Finally, we compared our catalytic system with commercially available imidazolium and phosphonium-based ILs (Table 4). The imidazolium-based IL [EMIm]NTf2 converts anisole with a yield of 77% (see Table 4, entry 1), whereas [BMIm]NTf2 shows a similar

• performance as TAAIL 6. Using IL 1,3-dibutyl-2-methylimidazolium NTf2 (Table, entry 3), carrying no hydrogen atom at the C2 position of the imidazolium ring, 86% of product were obtained. The phosphonium-based IL [P66614]NTf2 again shows an inferior performance compared to TAAIL 6. Upon changing the anion of

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

• proposed by the authors proceeded through cine-substitution. In the first step, the activation of imidazole 1-oxide 22 by oxalyl chloride led to the generation of imidazolium chloride 24, which transformed into intermediate 25 through nucleophilic substitution. Finally, the acidic hydrogen atom at C-2

• 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

• 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

Ionic multiresonant thermally activated delayed fluorescence emitters for light emitting electrochemical cells

• Merve Karaman,
• Abhishek Kumar Gupta,
• Subeesh Madayanad Suresh,
• Tomas Matulaitis,
• Lorenzo Mardegan,
• Daniel Tordera,
• Henk J. Bolink,
• Sen Wu,
• Stuart Warriner,
• Ifor D. Samuel and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2022, 18, 1311–1321, doi:10.3762/bjoc.18.136

• TADF emitter 2CzPN with imidazolium groups [16][17] (Figure 1a). The LEEC devices showed a maximum external quantum efficiency (EQEmax) of 0.39%, a maximum brightness (Bmax) of 13 cd m−2, and a peak electroluminescence (λEL) at 538 nm. The device performance suffered when the emissive layer was doped

• (Figure 2a). The calculations were based on model systems, DiKTa-OMe and DiKTa-DPA-OMe, respectively, wherein we replaced the imidazolium side chain of DiKTa-OBuIm and DiKTa-DPA-OBuIm, respectively, with a methyl group [30]. Compared to DiKTa (HOMO = −6.20 eV, LUMO = −2.23 eV, ΔEg = 3.97 eV), both

A versatile way for the synthesis of monomethylamines by reduction of N-substituted carbonylimidazoles with the NaBH₄/I₂ system

• Lin Chen,
• Xuan Zhou,
• Zhiyong Chen,
• Changxu Wang,
• Shunjie Wang and
• Hanbing Teng

Beilstein J. Org. Chem. 2022, 18, 1032–1039, doi:10.3762/bjoc.18.104

• acted as a nucleophile to attack the carbonyl carbon to cause the imidazolium ion to leave without reducing the carbonyl group. Although this work expands the application of N-substituted carbonylimidazoles, the reaction can still be regarded as a substitution reaction, which is attributed to the weak

First example of organocatalysis by cathodic N-heterocyclic carbene generation and accumulation using a divided electrochemical flow cell

• Daniele Rocco,
• Ana A. Folgueiras-Amador,
• Richard C. D. Brown and
• Marta Feroci

Beilstein J. Org. Chem. 2022, 18, 979–990, doi:10.3762/bjoc.18.98

• reactions and usually the product separation is easy [4][5]. Among ILs, imidazolium derivatives are the most studied, in part due to their ease of synthesis, low cost and diverse applications from solvents and reagents in synthesis, to supporting electrolytes in electrochemistry [6]. The imidazolium cation

• can be modified by the presence of a base or by a single electron cathodic reduction of the C–H between nitrogen atoms of the imidazolium ring (Scheme 1), inducing the formation of a N-heterocyclic carbene (NHC) [7][8]. In recent years, NHCs have achieved great success: they have been frequently used

• reduction of an imidazolium cation to NHC, in an undivided cell under flow conditions, coupled with the anodic generation of Cu(I) from a sacrificial anode to yield the corresponding N-heterocyclic carbene complex [34][35]. In this case, irreversible capture of the NHC by the metallic cation prevented NHC

Site-selective reactions mediated by molecular containers

• Rui Wang and
• Yang Yu

Beilstein J. Org. Chem. 2022, 18, 309–324, doi:10.3762/bjoc.18.35

• cavitand hosts were also modified with imidazolium cationic or carboxylic anionic feet [29]. Before the reaction, NMR analysis of the host–guest complex indicated that the bound guest was in yo-yo motions time-averaged between unsymmetrical J-shaped conformations and symmetrical U-shaped ones. Treatment of

Halides as versatile anions in asymmetric anion-binding organocatalysis

• Lukas Schifferer,
• Martin Stinglhamer,
• Kirandeep Kaur and
• Olga García Macheño

Beilstein J. Org. Chem. 2021, 17, 2270–2286, doi:10.3762/bjoc.17.145

• catalysts and asymmetric methodologies, a few innovative nonchiral alternative H-donor or halide-binding organocatalysts, like, e.g., tridentate phosphoramides [41], onium salts [42] such as Berkessel's pyridinium systems [43], or Huber's bis-iodo imidazolium [44] and neutral bridged 2,6-diiodo‐3,4,5

Constrained thermoresponsive polymers – new insights into fundamentals and applications

• Patricia Flemming,
• Alexander S. Münch,
• Andreas Fery and
• Petra Uhlmann

Beilstein J. Org. Chem. 2021, 17, 2123–2163, doi:10.3762/bjoc.17.138

• concentration of the polymer, but also by the nature of the anion as well as its concentration. Moreover, UCST behavior induced by BF4− was also detected in aqueous solutions of polypeptides, whose side chains contain charged pyridinium or imidazolium functionalities [290][291]. In contrast to single charged

Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects

• Shivani Gulati,
• Stephy Elza John and
• Nagula Shankaraiah

Beilstein J. Org. Chem. 2021, 17, 819–865, doi:10.3762/bjoc.17.71

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• ]arene. Pillararenes have electron-rich cavities that facilitate the combination with various electron-deficient guest molecules, such as alkylammonium, pyridinium, and imidazolium cations. Compared to other macrocycles, pillararenes exhibit a high degree of symmetry and rigidity, which gives them a

Selective recognition of ATP by multivalent nano-assemblies of bisimidazolium amphiphiles through “turn-on” fluorescence response

• Rakesh Biswas,
• Surya Ghosh,
• Shubhra Kanti Bhaumik and
• Supratim Banerjee

Beilstein J. Org. Chem. 2020, 16, 2728–2738, doi:10.3762/bjoc.16.223

• [36][37][38], conjugated polymers [39][40][41][42], quantum dots [43][44] and sensors based on organic receptors such as imidazolium, ammonium, guanidinium [45][46][47][48][49][50][51][52], etc. have also been developed. Imidazolium based synthetic receptors typically utilize a combination of

• electrostatic and (C–H)···O− hydrogen bonds involving the acidic proton at the 2-position of the imidazolium moiety to bind to ATP and other phosphate analytes [46]. A number of cyclophanes and tweezers [53][54][55][56] have been reported possessing the following common structural features: a) the presence of

• multiple imidazolium groups to overcome the high hydration enthalpy of phosphates and b) the imidazolium groups are connected to aromatic moieties such as anthracene, pyrene, etc. The variation in the luminescence of the aromatic moieties signals the binding event and furthermore, they provide additional

Optical detection of di- and triphosphate anions with mixed monolayer-protected gold nanoparticles containing zinc(II)–dipicolylamine complexes

• Lena Reinke,
• Julia Bartl,
• Marcus Koch and
• Stefan Kubik

Beilstein J. Org. Chem. 2020, 16, 2687–2700, doi:10.3762/bjoc.16.219

• binding of these anions to the immobilized receptor units strengthened their interaction with a simultaneously present bis(imidazolium) ion, which in turn caused nanoparticle crosslinking [16][17]. Our group recently showed that a mixed monolayer-protected AuNP containing solubilizing triethylene glycol

Synergy between supported ionic liquid-like phases and immobilized palladium N-heterocyclic carbene–phosphine complexes for the Negishi reaction under flow conditions

• Edgar Peris,
• Raúl Porcar,
• María Macia,
• Jesús Alcázar,
• Eduardo García-Verdugo and
• Santiago V. Luis

Beilstein J. Org. Chem. 2020, 16, 1924–1935, doi:10.3762/bjoc.16.159

• corresponding Pd–NHC complexes 4a and 4b (Scheme 1) were obtained by treatment of the supported imidazolium species with Pd(OAc)2 in the presence of a base. The amount of immobilized NHC ligand was determined by elemental analysis, while the palladium loaded on the polymer was determined by ICP analyses (see

• inactive species and keeping their activity for further catalytic cycles. Three different SILLPs were evaluated displaying different imidazolium substitution patterns and a loading of IL-like fragments of 13–24% by weight. Figure 4 summarizes the results obtained for this study. The presence of SILLPs

• affected both activity and Pd leaching. Regarding the activity, the presence of methyl imidazolium groups in SILLP 9a slightly reduced the catalytic activity, while the presence of butyl- and methyldecylimidazolium units (SILLPs 9b and 9c, respectively) led to more active systems. This can be clearly

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

A systematic review on silica-, carbon-, and magnetic materials-supported copper species as efficient heterogeneous nanocatalysts in “click” reactions

• Pezhman Shiri and
• Jasem Aboonajmi

Beilstein J. Org. Chem. 2020, 16, 551–586, doi:10.3762/bjoc.16.52

• Cu(I)-catalyzed cyclization between CRGO–N3 (93) and 1-propargyl-3-methylimidazolium bromide (94) was used to attach the imidazolium moiety to the surface of the CRGO. Finally, a graphene-containing copper complex of N-heterocyclic carbene, (NHC)-Cu (96), was produced via proton exchange of the

• imidazolium scaffold with a Cu(I) (Scheme 21). The reaction between benzyl azide and alkynes proceeded in deuterated THF at 40 °C within 72 h using 2.0 mol % of the catalyst to obtain the desired products with good to high yields (Scheme 21). The nanocatalyst 96 could be readily recycled for use in more than