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Keywords
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Benzoin Condensation, Cascade
reaction, N-Heterocyclic carbenes, Oxidation,
tri(tetra)-Substituted imidazoles.
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Abstract
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In this study, a novel and efficient onepot
tandem synthesis of 2,4,5-tri- and 1,2,4,5-tetrasubstituted
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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