Covalently anchored sulfonic acid on silica gel as an efficient and reusable heterogeneous catalyst for the one-pot synthesis of Hantzsch 1,4-dihydropyridines under solvent-free conditions

A highly efficient one-pot synthesis of Hantzsch 1,4-dihydropyridines under solvent-free conditions catalyzed by sulfonic acid covalently anchored onto the surface of silica gel is reported here. All types of aldehydes, including aromatic, unsaturated, and heterocyclic aldehydes, gave excellent yields. The silica gel/sulfonic acid catalyst (SiO2-SO3H) is completely heterogeneous and can be recycled for eight consecutive runs without significant loss of activity.