Wells-Dawson heteropolyacid supported on silica: a highly efficient catalyst for synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles.

Heteropolyacid H(6)P(2)W(18)O(62)·24H(2)O (WD) supported on silica (WD/SiO(2)) has been used as an effective catalytic system for the synthesis of various 1,2,4,5-tetrasubstituted imidazoles by four-component condensation of benzil, aldehydes, amines and ammonium acetate under solvent-free conditions. This approach can be useful for three-component synthesis of 2,4,5-trisubstituted imidazoles. The same reactions were repeated by using benzoin instead of benzil.