Benzimidazolium ions

The constancy of the values of klm and kBlm, rather than the values of k, in Table I suggests that the basic form of imidazole or benzimidazole is the catalytic species, and that the imidazolium or benzimidazolium ion is not. This interpretation is in agreement with that of Gurd (8) and of Bruice and Schmir (3) on the catalyzed hydrolysis of p-nitrophenyl acetate by imidazole. Bronsted and Guggen-... 

Heterocyclic compounds Substituted Benzimidazolium ions Various 58a, b... 

In 1999, the first annulated carbene derived from benzimidazole, l,3-bis(2,2-dimethylpropyl)benzimidazolin-2-ylidene, was prepared by the reduction of A/,N -dialk ylated benzimidazol-2-thione with Na/K in toluene [44]. Frequently, benzimidazolium ions containing less bulky Af-alkyl groups interconvert rapidly into enetetramine derivatives. Even when the formation of these compounds can be avoided by sterically demanding substituents, the final generation of the carbene may fail. 

Cyanations of benzimidazolium or benzimidazole N-oxides have been reported (93CHE127). Cyanopyrazoles are formed by irradiation of pyrazoles in the presence of cyanide ions in photosubstitution reactions. 

Although isolated in small amounts, the pyridinium salts 282 (arising from the iodine-mediated oxidation of DHPs 281) do not afford benzimidazolium salts 279 in the presence of isocyanides. A likely pathway may start with the iodo-dihy-dropyridinium intermediate 280, which can be formed by interaction of iodine with the reactive double bond of the DHPs (Scheme 44). The isocyanide may subsequently attack these species to generate the nitrilium ion T, which interacts with a second equivalent of isocyanide to form cation U. This intermediate undergoes an intramolecular trapping by the enamine unit to close the bicyclic system V... 

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