Synthesis and tautomerism of 2-phenacyl-1H-benzimidazoles and their hydrogen bromide salts

2-Phenacyl-1H-benzimidazoles were prepared by the acylation of 2-methylbenzimidazole using aroyl chlorides with subsequent alcoholysis or aminolysis of the N,C,O-triacylation products obtained. Treatment of the 2-phenacyl-1H-benzimidazoles with hydrobromic acid gave the corresponding salts. The structure of the products was supported by IR, 1H and 13 C NMR, and HMBC spectroscopy as well as by quantum-chemical calculations. 2-Phenacyl-1H-benzimidazoles in DMSO-d6 solution were found to display predominantly imino-enamino tautomerism, while their salts were found to display predominantly keto-enol tautomerism.