N‐Heterocyclic Carbene‐Catalyzed Condensation/ Oxidation/ Cyclization/ Aromatization Cascade for the Synthesis of Tri‐ and Tetra‐Substituted Imidazoles

N-Heterocyclic carbene-catalyzed one-pot synthesis of highly substituted imidazoles from aldehydes and amines.

Abstract

In this study, a novel and efficient one-pot tandem synthesis of 2,4,5-tri- and 1,2,4,5-tetra-substituted imidazoles is described. In the first step of the sequence, benzil is formed via benzoin condensation catalyzed by N-heterocyclic carbene, followed by in situ aerobic oxidation. Next, it is reacted with another aldehyde and ammonium acetate (or amine) to produce the polysubstituted imidazole. The reaction proceeds smoothly in high yield and short reaction time in ethanol as a green solvent. The current strategy shows high functional group tolerance with respect to aldehydes and avoids the need for ligands and reducing agents. This method allows the synthesis of complex molecules in a one-pot procedure without isolating intermediates.

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