Imidazolium derivatives, and

Apart from LiMe the adduct A could also be trapped with cyanamide. The cation 1 reacted with N = C-NR2 in excess to form the novel imidazolium complexes 5 (Scheme 4). The formation of 5 corresponds to a [2+2+1] cyclization. Isomers of 5 have not been detected. The complexes 5 are derived from adduct A by nucleophilic addition of N = C-NR2 to the carbon atom of the NCNR2 substituent of A. The cyclization possibly proceeds via the sequence (a) formation of a metallacycle, (b) reductive elimination of a cationic imidazolium derivative and (c) formation of 5. Isomers which are derived from an attack of NSC-NR2 at the CNPh substituent of B or at the carbene carbon atom of either A or B have not been observed. 

Duan G, Zhu N, Yam VW-W (2010) Syntheses and photochromic studies of dithienylethene-containing imidazolium derivatives and their reactivity towards nucleophiles. Chem Eur J 16 13199-13209... 

Scheme 12.58 Divergence between triazolium- and imidazolium-derived NHCs in lactone formation with hydroxyenones...

On the other hand, it has been demonstrated that the a-D-glucopyranosyl aceto-nitrilium ions are stereospecifically generated from the corresponding oxocarbenium ions in dry acetonitrile [43-45]. These results indicate that the acetonjtrilium ions are axially oriented by an anomeric effect. Recently, it has been concluded from the conformational analyses of glucopyranosyl-ammonium and glucopyranosyl-imidazolium derivatives that the reverse anomeric effect does not exist [46,47]. 

It should be noted that while enyne metathesis is considered incompatible with molybdenum catalyst 1, ruthenium catalysts other than the Grubbs type also promote the reaction. Semeril et al. [103] reported efficient enyne RCM with a catalyst conveniently generated in situ from [RuCl2(p-cymene)]2,1,3-bis(mesityl)imidazolium chloride and caesium carbonate. Interestingly the authors found that the in situ derived system gave better results than the isolated catalyst. One of the most impressive examples of the use of enyne RCM is the total synthesis of (-)-longithorone by Layton et al. [104]. Inspired by a pro-... 

QC m] [various] [C4C Ciim][BF4] Pd(PPh3)4, Pd(OAc)2 and many others Na2C03 110 °C. Broad study used to identify the active catalyst species both imidazoylidenes (carbenes derived from the imidazolium cation) and halide ligands are implicated in the catalytic cycle products extracted with Et20 catalyst stable for at least 4 runs. [105]... 

According to the previous results published in 1992, Mesic et al. (1994) synthesized four new / -methylphenyl imidazolium derivatives (20-23) (Figure 66.16) and compared their biological activity to the corresponding... 

However, another study was an example of nature appreciation—the structure of thiamine was varied to learn what was special about the particular thiazolium derivative that was natural thiamine (11). As a chemical catalyst—ignoring the question of what effect changes would have on the ability of the coenzyme to bind to the proteins that have evolved to use it—thiamine proved to be the optimal relative to other related structures because of a balance of catalytic ability and chemical stability. The anion 4 derived from an imidazolium ring instead of a thiazolium ring was a weaker catalyst but was more stable in water (10). [The imidazolium aiuon and its dihydro derivative have proven to be very useful metal ion ligands, including... 

N-Acylimidazoles (azolides) have continued to provide a synthetic source of acid derivatives,and the various olysis reactions of these compounds have been studied. " The reactions of acetyl-imidazolium ions with amines have been found to depend largely on amine basic) The thermal decarboxylation of JV-alkoxycarbonylimid-... 

Li et al. [89, 90] synthesized a series of new fluoroalkoxycyelophosphazene and aryloxycyclophosphazene derivatives substituted with imidazolium ILs and studied their tribological properties on an Optimol SRV-IV oscillating friction and wear tester under ambient conditions. They found that these ILs exhibited better anti wear ability and load-carrying capacity in steel/steel contacts than X-IP. 

The catalytic efficiency of the RTILs derived from l-butyl-3-methylimidazolium (bmim) cation is influenced by the structure of the imidazolium moiety and the counteranion following the order [bmim][MeSO ]>[bmim][HSO ] [bmim]... 

The isolation of histidine, the imidazolium derivative (8), and other non-protein amino-acids from the seaweed Gracilaria secundata may be of general interest.11... 

Benzyl alcohols. After transmetaUation arylboiDnic acids are converted into aryl-rhodium species that are nucleophilic toward various aldehydes. A very active catalyst (1) is that derived from Rh2(OAc)4, l,3-bis(2,6-diisopropylphenyl)imidazolium chloride and r-BuOK. ... 

Basically, an analogous situation is found with imidazolium, thiazolium, and their benzo-annelated derivatives (9.24), although byproducts may interfere with a straightforward addition to diazo compounds (see Regitz et al., 1985). 

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