Abstract
Sulfamic acid efficiently catalyzes the three‐component condensation reaction of aldehydes, 1,3‐dicarbonyl compounds, and urea/thiourea under solvent‐free conditions to afford the corresponding dihydropyrimidinones and thio‐derivatives in high yields. Silica sulfuric acid is also found to be an efficient catalyst for the Biginelli reaction under solvent‐free conditions. Compared to the classical Biginelli reaction conditions, this new method consistently has the advantage of giving good yields and requiring short reaction times.