Grindstone chemistry: protic ionic liquid-substrate tuned green synthesis of 1,2-disubstituted and 2-substituted benzimidazoles with outstanding selectivity

An environmentally benign and highly catalyst-substrate controlled synthesis of 1,2-disubstituted and 2-substituted benzimidazoles with outstanding selectivity has been developed through grinding a mixture of o-phenylenediamines, suitable aldehydes and an imidazolium trifluoroacetate protic ionic liquid catalyst. The newly developed metal-free catalysis approach produced 1,2-disubstituted benzimidazoles from aromatic aldehydes bearing electron donating group, whereas aromatic aldehydes possessing electron withdrawing groups and aldehydes with 2-alkoxy substitution selectively furnished 2-substituted benzimidazoles and their chiral analogues. Low energy consumption, short reaction time and solvent-free synthesis make this methodology green, providing a useful contribution to the existing procedures available for the synthesis of benzimidazole derivatives.