3- imidazolium bromide, reaction

No examples of such reactions have been disclosed. Displacement of halogens on the parent heterocycle through metal-catalyzed processes have surprisingly not been reported to our knowledge on the neutral heterocycle. Recently, Suzuki-Miyaura cross-coupling reactions of imidazolium bromide 113 with various boronic acids or esters were reported <2005T6207> to proceed in good yield, without deprotonation at the C-3 position (Scheme 35). 

Shen and co-workers reported a method for preparing lanthanide-NHC halides through protonolysis.75 Reaction of the imidazolium bromide salt with anionic LiLn(N Pr)4 affords salicylaldiminato-functionalized NHC-lanthanide bromides (Scheme 33). The complexes were all characterised by single crystal X-ray diffraction and exhibit capped octahedral geometries. The NHC-Ln MIC bond angles decrease Nd>Sm>Er> which is consistent with decreasing ionic radii, and the Ln-NHC bond lengths also... 

Recently, the reactivity of N-heterocyclic carbenes with bromine and some chloride sources were reported. Imidazolium chloride salts are sometimes obtained as side products when carbene (1) is reacted with main group species to produce main group carbene adducts. However, they can be prepared directly from the reaction of carbene (1) (R = Mes, R = H) with chloroalkanes, such as hexachloroethane in acetonitrile (134). Reaction of carbene (1) (R = Mes, R = H) with Br2 or 1,2-dibromoethane affords the 2-bromo-l,3-bis(2,4,6-trimethylphenyl) imidazolium bromide (135). 

A broader exploitation of cellulose solubility in ionic liquids lies in modification of cellulose into more useful forms. Cellulose acetate is currently the most useful derivative of cellulose, with uses in photographic film, as a synthetic fibre and as a component of adhesives. Acetylation of cellulose has been carried out effectively in l-allyl-3-methylimidazolium chloride [Amim][Cl], [C4mim CI], [C2mim][Cl], l-butyl-2,3-dimethylimidazolium chloride [C4dmim][Cl] and l-allyl-2,3-dimethyl-imidazolium bromide [Admim][Br] [136, 159-162], The first report of cellulose acetylation in an ionic liquid involved a one-step reaction in [Amim][Cl] without catalyst, yielding cellulose acetate with a controllable degree of substitution [136], Yields of cellulose acetate of up to 86% have been obtained via reaction in [C4mim] [Cl] at 80 °C for 2 h [160],... 

To end this section, it has to be mentioned that there is a single example of a conjugate Friedel Crafts alkylation involving enones as Michael acceptors. In particular, a camphor-based sulfonic acid (94) has been used as catalyst in the reaction of indoles with chalcones (Scheme 4.57). It has also to be noted that the best conditions involved the use of catalyst 94 together with an ionic liquid (l-butyl-3-methyl-l//-imidazolium bromide BmimBr). However, although excellent yields were obtained for a set of different substrates tested, the enantioselectivities remained in rather low values. 

Since MBH reactions carried out with common ionic liquids, such as [bmim]pC], give lower to moderate yields, more recently, Tsai el al. have synthesized a new and highly active di-naphthalene imidazolium salt. They found that l,3-bis[2-(naphthalene-2-yloxy)propyl]imidazolium bromide (306) promoted... 

In 2012, Zhu et al. [60] designed and S5mthesized a novel bifunctional IL-supported iodoarene-TEMPO catalyst 162 with two catalytic sites, which are the iodoarene and TEMPO moieties. Reaction of l-(bromomethyl)-4-iodoben-zene with 1-methylimidazole gave l-(4-iodobenzyl)-3-methylimidazolium bromide 161 followed by metathesis of Na[TEMP0-0S03] with imidazolium bromide to deliver final IL-supported iodoarene-TEMPO bifunctional reagent 162 (Scheme 20) [60]. IL-anchored hypervalent iodine reagents were demonstrated to be useful for the efficient... 

The cation of an ionic liquid can also influence the acidity of a system and a weak Lewis acidity is attributed by the imidazolium ion itself. The catalytic effect of imidazolium bromide melts in Diels-Alder reactions is reported to be related to this weak acidity of the imidazolium ion. Moreover, the H atom in the a-position of an imidazolium ion possesses significant Bronsted acidity which could be beneficial for reactions involving transition metal complexes as in situ carbene complexes can be formed in the presence of base. °... 

Aryl nitriles 82 and 83 were synthesized from the corresponding iodide 84 and bromide 85 in imidazolium bromide ionic solvent (86). The described protocol using either excess copper cyanide or catalytic copper(I) iodide and sodium cyanide, allows for these reaction to be run at between 90 and 130 °C. Isolation of the products is still somewhat problematic, however, the catalyst can be recycled from this medium and effectively re-used. ... 

The use of imidazolium-based ionic liquids in Pd-catalyzed Heck reactions always carries with it the possibility of in situ formation of Pd-carbene complexes (for more details see Section 5.2.2.3). The formation of these under the conditions of the Heck reaction was confirmed by investigations by Xiao et al. [30], who described a significantly enhanced reactivity of the Heck reaction in [BMIM]Br in relation to the same reaction in [BMIM][Bp4] and explained this difference by the fact that formation of Pd-carbene complexes was observed only in the bromide melt. 

The use of imidazolium salts for in situ catalyst formation was shown to be optimal for the coupling of TMS-protected alkynes even with sterically demanding aryl bromides and avoids the formation of homocoupling-derived products. For this reaction, Nolan reported that the activation of chlorobenzene by this catalytic system was possible in moderate yield [125] (Scheme 6.41). 

The first examples utilising A-heterocyclic carbenes as ligands in the Buchwald-Hartwig amination involved the in situ formation of the catalyst from the corresponding imidazolium salt and a Pd(0) source. Nolan reported IPr-HCl/PdjCdbalj as a catalytic system for the amination of aryl chlorides in excellent yields, using different types of amines, anilines, and also imines or indoles [142,143] (Scheme 6.46). Hartwig showed later that in some cases the reactions could be performed at room temperature and without anhydrous conditions even for aryl chlorides [ 144]. This was later shown for the less challenging bromides and iodides [145,146]. 

Route A 1- is very convenient for the substitution of OH groups by bromide or iodide. The reaction conditions are relatively mild (acetonitrile, room temperature, and reflux for 1—3 h, neutral medium). The activating halide (methyl iodide, ally or benzyl bromide) is added in excess (5 equivalents) or in large excess (10 equivalents) when the resultant halide is nearly as reactive as the activating halide. The imidazolium-iV-carboxylates are the important intermediates, which undergo a displacement reaction to give the halides,... 

Besides the advantage of recyclability, reactions in ionic liquids are generally faster and are run under milder conditions than reactions with conventional solvents. Further activation may come from ultrasonic agitation.520 Since the majority of ionic liquids used are imidazolium salts, the effect of these solvents can be at least partly attributed to the in situ formation of carbene complexes (Section 9.6.3.4.10).521 Cross-coupling of ArB(OH)2 can also be efficiently performed in ionic liquids based on long-chain tetraalkylphosphonium salts, in which case aryl bromides and some aryl chlorides can be processed in the presence of the trivial ligand PPh3.522... 

Similar imidazolium ylides are implicated in the aroylation of TV-phenyl benzimidoyl chlorides (92CPB2627), and in reactions of 1-substituted imidazoles with cyanogen bromide to form 2-cyano- or 2-bromo-imidazoles (88S470). 

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