Application of a Keplerate type giant nanoporous isopolyoxomolybdate as a reusable catalyst for the synthesis of 1,2,4,5-tetrasubstituted imidazoles

The Keplerate-type giant nanoporous isopolyoxomolybdate (NH4)42[MoVI72MoV60O372-(CH3COO)30(H2O)72], denoted {Mo132}, has been used as a catalyst for the synthesis of 1,2,4,5-tetrasubstituted imidazoles by the one-pot, four-component thermal reaction of benzil with aromatic aldehydes, primary amines, and ammonium acetate under solvent-free conditions. The catalyst was prepared according to a previously published literature procedure using inexpensive and readily available starting materials, and subsequently characterized by FT-IR, UV and X-ray diffraction spectroscopy, as well as microanalysis. The results showed that {Mo132} exhibited high catalytic activity towards the synthesis of 1,2,4,5-tetrasubstituted imidazoles, with the desired products being formed in good to high yields. Furthermore, the catalyst was recyclable and could be reused at least three times without any discernible loss in its catalytic activity. Overall, this new catalytic method for the synthesis of 1,2,4,5-tetrasubstituted imidazoles provides rapid access to the desired compounds following a simple work-up procedure, and avoids the use of harmful organic solvents. This method therefore represents a significant improvement over the methods currently available for the synthesis of tetrasubstituted imidazoles.

Graphical Abstract{Mo132} efficiently catalyzed the synthesis of 1,2,4,5-tetrasubstituted imidazoles under solvent-free conditions. The method was relatively fast and high yielding, and the work-up was easy. The catalyst used at least four times without any substantial reduction in its catalytic activity.Figure optionsDownload full-size imageDownload as PowerPoint slide