An advantageous synthesis of 2-substituted benzimidazoles using polyphosphoric acid. 2-(pyridyl)-1H-benzimidazoles, 1-alkyl-(1H-benzimidazol-2-yl)pyridinium salts, their homologues and vinylogues

Article abstract of DOI:10.1055/s-1992-26121

The title 2-substituted benzimidazoles are prepared by a highly efficient one-pot procedure, cyclodehydration of the corresponding accessible carboxylic acids and 1,2-arylenediamines, using polyphosphoric acid as the catalyst and solvent in a condensation of the type found in the Phillips benzimidazole synthesis. The method has been adapted and proved to be extremely useful for 1-alkyl-(1H-benzimidazol-2-yl)pyridinium tetrafluoroborates with a methylene and vinylene interannular moiety.