Sulfonic acid functionalized silica: an efficient heterogeneous catalyst for a three-component synthesis of 1,4-dihydropyridines under solvent-free conditions.

Sulfonic acid functionalized silica catalyzed the three-component reaction of aromatic amines, alpha,beta-unsaturated aldehydes and beta-keto esters forming the corresponding 1,4-dihydropyridines in short reaction times and in high yields.