Formation of zwitterionic salts via three-component reaction of benzimidazolium bromides, aromatic aldehydes and 1,3-indanedione

Abstract

The three-component reaction of N-butyl-N′-phenacylbenzimidazolium bromide, aromatic aldehydes and 1,3-indanedione in ethanol in the presence of triethylamine as base catalyst resulted in the unusual charge-separated zwitterionic salts in good yields. Similar reactions with N-butyl-N′-(4-nitrobenzyl)- and N-butyl-N′-ethoxycarbonylmethylbenzimidazolium bromide also afforded the corresponding zwitterionic salts. Furthermore, ¹H NMR spectra and single crystal structures indicated that the zwitterionic salts usually exist as two kinds of conformational isomers due to hindered interconversion of the different conformations.