Phthalimide-N-sulfonic acid: a new and efficient organocatalyst for the Biginelli reaction under solvent-free conditions Hamzeh Kiyani • Maryam Ghiasi Received: 30 May 2014 / Accepted: 7 July 2014 Ó Springer Science+Business Media Dordrecht 2014 Abstract 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. Keywords Phthalimide-N-sulfonic acid Á Organocatalyst Á Biginelli-3CR Á 3,4- Dihydropyrimidin-2(1H)-ones/thiones Á Solvent-free conditions Introduction The one-pot multicomponent reaction (MCR) was an attractive broad area of research in the synthesis of N-containing heterocyclic scaffolds such as the 3,4- dihydropyridin-2-1H-(ones)/3,4-dihydropyridin-2-1H-(thiones) (DHPMs) and their heterocyclic derivatives [1–19]. A one-pot process in organic synthetic chemistry that generates DHPMs via MCR in a single operation is called the Biginelli 3-component reaction (Biginelli-3CR). Since the 3CR synthesis of ethyl-6-methyl- Electronic supplementary material The online version of this article (doi:10.1007/s11164-014-1766-7) contains supplementary material, which is available to authorized users. H. Kiyani (&) Á M. Ghiasi School of Chemistry, Damghan University, 36715-364 Damghan, Iran e-mail: hkiyani@du.ac.ir 123 Res Chem Intermed DOI 10.1007/s11164-014-1766-7