Tetrabutylammonium hexatungstate [TBA]2[W6O19]: Novel and reusable heterogeneous catalyst for rapid solvent-free synthesis of polyhydroquinoline via unsymmetrical Hantzsch reaction

A novel, efficient, and environmentally friendly method for the synthesis of polyhydroquinoline derivatives by a one-pot, four-component unsymmetrical Hantzsch condensation of dimedone, aldehydes, ethyl acetoacetate, and ammonium acetate in the presence of a catalytic amount of tetrabutylammonium hexatungstate [TBA]2[W6O19] under solvent-free conditions has been developed. The results showed that this heterogeneous catalyst has high catalytic activity and the desired products were obtained in good to high yields. Moreover, the catalyst was found to be reusable and considerable catalytic activity was still achieved after the fifth run.