Synthesis of N-unsubstituted 2-arylpyrazolo[1,5-a]benzimidazoles from 1-benzylideneamino-2-methylbenziraidazole and the role of acylotropic and acylotropic-prototropic isomerization

摘要

2-Aryl-4H-pyrazolo[1,5-a]benzimidazoles were synthesized for the first time from 1-benzyl-ideneamino-2-methylbenzirnidazole by the benzoylation of the methyl group followed by the cyclization of the resulting vinyl acylates in concentrated HCl. The key steps of the process were studied by quantum chemical methods for model systems. It was shown that the concerted intramolecular acylotropic and acylotropic-prototropic transformations play an important role in this process.