Phospho sulfonic acid: an efficient solid acid catalyst for the facile preparation of 1,4-dihydropyridines

A simple and mild one-pot three-component reaction for the preparation 1,4-dihydropyridines has been developed from various aldehyde substrates, 1,3-dicarbonyl compounds (dimedone) and ammonium acetate (Hantzsch method) in the presence of a catalytic amount of phospho sulfonic acid (PSA) as an efficient and heterogeneous solid acid in EtOH at room temperature. Preparation of PSA is straightforward and handling of the reagent is also easy. The attractive features of this protocol are: (i) The elimination of corrosive liquid acids; (ii) the use of an inexpensive and relatively non-toxic catalyst, and (iii) reusability of the catalyst.