Phthalimide-N-sulfonic acid: a new and efficient organocatalyst for the Biginelli reaction under solvent-free conditions

Phthalimide-N-sulfonic acid (PISA) was straightforwardly synthesized via addition of chlorosulfonic acid to a solution of potassium phthalimide in dry dichloromethane. This reagent is found to be an efficient solid acidic catalyst in the Biginelli reaction. The three-component reaction of aryl aldehydes, urea/thiourea, and ethyl acetoacetate or acetylacetone occurs by means of 10 mol % of PISA in solvent-free reaction conditions (SFRCs) at 120 °C. The present methodology is a green approach to access a series of 3,4-dihydropyrimidin-2(1H)-ones/thiones in high yields. In addition, the use of PISA as the catalyst offers several notable features such as simple operational procedure, no use of hazardous organic solvents, and recyclability of catalyst.