Silica‐bonded S‐sulfonic Acid as a Recyclable Catalyst for Synthesis of 2,3‐Dihydroquinazolin‐4(1H)‐ones

2,3‐Dihydroquinazolin‐4(1H)‐one derivatives were synthesized via a one‐pot, three component reaction of isatoic anhydride and an aromatic aldehyde with ammonium acetate or primary amine catalyzed by silica‐bonded S‐sulfonic acid in ethanol at 80°C. The reaction work‐up is simple and the catalyst is easily separated from the products by filtration. The heterogeneous catalyst was recycled for ten runs upon the condensation reaction of isatoic anhydride and 4‐chlorobenzaldehyde with ammonium acetate without losing its catalytic activity.