Facile synthesis of benzimidazolin-2-chalcogenones: Nature of the carbon–chalcogen bond

A new method using chalcogen nucleophiles E2−/E22− (E = S, Se, Te) for the convenient and high yield synthesis of benzimidazolin-2-chalcogenones has been developed. The reaction of strong nucleophiles E2−/E22− with various benzimidazolium salts under mild conditions afforded benzimidazolin-2-chalcogenones (10a–10g) in better yield compared to the other methods involving E0 powder. Benzimidazolin-2-tellurones were found to be unstable when pyridyl/phenyl groups were bonded to one of the nitrogens of the benzimidazolium salts and the reaction led to the isolation of the corresponding diamines (12a and 12b). The selenones/tellurones could be easily oxidized to the corresponding dihaloderivatives (16a–16e) by the reaction of the chalcogenones with bromine/iodine. The nature of the carbon–chalcogen double bond has been investigated with the help of single crystal X-ray, NMR spectroscopy and Density Functional Theory (DFT) calculations.