Syntheses of heterocyclic compounds. Part XXVII. Substitution reactions and rearrangements of benzimidazole N-oxides

Abstract

Treatment of benzimidazole N-oxides with a variety of nucleophiles results in ring substitution with concomitant loss of the N-oxide oxygen atom. Thus, reactions with HCl, KCl, SOCl₂, SO₂Cl₂, and various organic acid chlorides yield various chlorinated isomers. The co-action of toluene-p-sulphonyl chloride and the nucleophiles CN^–, SCN^–, N₃^–, butane-1-thiol, butylamine, or aniline results in ring substitution, whereas co-action with the nucleophiles Br, I, and butane-1-thiolate causes deoxygenation only. With toluene-p-sulphonyl chloride and alkali a novel rearrangement to NN′-polymethylenebenzimidazolones occurred in the case of some N-oxides. These reactions are rationalised and are shown to have considerable synthetic utility.