1- benzimidazolium salts

In situ derived systems, in general, performed similarly to preformed complexes, in telomerisation of butadiene with MeOH, Tables 4.1 and 4.2 [68,70,71,77,78], In situ systans may be generated from free NHC or from imidazolium salt in combination with an appropriate Pd(0) or Pd(ll) source. Typically, 2-4 equivalents of imidazolium salt relative to Pd have been nsed [68,70,77], In situ catalysts derived from mono- and bis-Fc-snbstituted (Fc = ferrocenyl) imidazohnm and benzimidazolium salts (64-68) (Table 4.2) showed interesting telomerisation activities ascribed to the steric bulk of the Fc substituents [70]. Unsymmetrical salts 65 and 66 bearing A -Fc and A -Me... 

The abstraction of a hydride is an additional route for the preparation of ben-zimidazolium salts Treatment of 2,3-dihydro-1 /f-benzimidazoles with tritylium tetrafluoroborate generates the benzimidazolium salt and triphenylmethane [Eq. (6)].44... 

As mentioned earlier, triazolium salts can be converted into 5-methoxy-4,5-dihydro-lH-triazoles by reacting them with sodium methanolate in methanol. The heterocycles eliminate methanol upon heating in vacuo [Eq. (21)] and the formed triazolin-5-ylidenes can then be isolated. " The same method works with imidazolium and benzimidazolium salts." ... 

Figure 15.9. Strategies for the preparation of benzimidazoles and mechanism of benzimidazolium salt formation. X O, S.

Methylbenzimidazole with DMAD in acetonitrile gave134 the yellow 360, readily oxidized by bromine in perchloric acid to a pyrido-[l,2-a]benzimidazolium salt, and an isomeric red compound originally thought to have structure 357, and consequently it was surprising that oxidation did not follow the same course as for 360. The red compound is best prepared from the reactants in toluene and has now been identi-... 

Addition of DMAD to the benzimidazolium salt 387 gave the cycloadduct 388.214... 

A recent discovery has been the unprecedented double insertion of isocyanides into 1,4-dihydropyridines, bearing an electron-withdrawing group at the 3-position, resulting in the formation of substituted benzimidazolium salts 298 (Scheme 68) <2007AGE3043>. 

Fig. 13 Chemical structures of methylene blue and ferrocenic benzimidazolium salts. R is an...

Distillation of solid benzodiazepinium salts may also lead to the formation of a ketone and a benzimidazolium salt (65JCS3785). A number of benzodiazepinium salts contain water of crystallization, and this, or adsorbed water, can presumably participate in the reaction. In the absence of... 

The most common way to prepare N-heterocyclic carbenes is the deprotonation of the corresponding azolium salts, like imidazolium, triazolium, tetrazolium, pyrazolium, benzimidazolium, oxazolium or thiazolium salts or their partly saturated pendants, with the help of suitable bases. The pJCa value of imidazolium and benzimidazolium salts was determined to be between 21 and 24, which puts them right in between the neutral carbonyl carbon acids acetone and ethyl acetate [41,42], Arguably, imidazolium-based carbenes have proven to be especially versatile and useful and their synthesis should be discussed in more detail. The synthesis of imidazolium salts has been developed over many decades and numerous powerful methods exist [43]. 

The reaction of triazolium and benzimidazolium salts with sodium methoxide yields the corresponding methoxy-triazoles and benzimidazoles [30,31], which can be also used as triazolilydene and benzimidazo-lilydene precursors. Notably, adduct formation does not occur for certain unsaturated imidazolium salts with a C = C backbone. For the latter, reaction with KOBu results in direct deprotonation to the free NHC (Scheme 8, also shows the reaction of a dihydroimidazolium salt with KOBu ) [32],... 

Benzimidazoles, 2,3-dihydro-, by Nu addition at C-2, 56, 203 Benzimidazole, 2-fluoro-, 59, 272 Benzimidazole, 1-methyl-, ring expansion to chloroquinoxalines, 59, 305 Benzimidazole, l-methyl-2-(5 -methyl-2 -thienyl)-, bromination, 57, 319 Benzimidazole 3-oxides, chloro-deoxygenation, 59, 270 Benzimidazoles, 2-perfluoroalkyl-, 60, 25 Benzimidazoles, 2-(l-pyridinio)-, 60, 204 Benzimidazoles, 2-(2-pyridinioethyl)-, elimination reactions, 60, 246 Benzimidazoles, tetrafluoro-, 59, 14 Benzimidazole-2-carboxylic ester 3-oxide, 7-nitro-5-trifluoromethyl-, 60, 17 Benzimidazolium salts, l-amino-3-alkyl-, reaction with activated acetylenes, 56, 138... 

The achiral analogue of the binaphthyl scaffold is the biphenyl backbone. An example comes from Chen et al. [362] who synthesised a bis-benzimidazolium salt starting from 2,2 -diaminobiphenyl (see Figure 3.114). In contrast to the bis-carbene in Figure 3.113, the... 

Figure 4.20 Synthesis of phenoxy functionalised benzimidazolium salts and theirpalladium(ll) complexes.

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