Use of starch–sulfuric acid and steam as a bio and recyclable system for Hantzsch reaction

In recent years, much attention has been paid to the synthesis of 1,4-dihydropyridines (1,4- DHPs) due to their relevant biological activity [1]. The classicalmethods for the synthesis of 1,4-DHPs is the Hantzsch multicomponent synthesis between an aldehyde, a 1,3- dicarbonyl compound and a source of ammonia, for example, ammonium acetate or an amine in the presence of different acid–basic catalysts[2].Recently, the direction of science and technology has been shifting toward more eco-friendly, natural product resources and reusable catalysts. Natural biopolymers are attractive candidates in the search for solid support catalysts [3]. Starch–sulfuric acidwas prepared by reaction between starchand chlorosulfonic acid. This catalyst has been used for some multicomponent reactions [4].Nowwe report an efficient and convenient procedure for the One-Pot synthesis of ethyl acetoacetate, aromatic aldehydes and ammonium acetate, by using heterogeneous catalyst starch–sulfuric acidunder solvent-free and steam conditions to produce the 1,4- dihydropyridine derivatives in excellent yields (Figure 1). Steam conditions improved the Hantzsch reaction and the yields of 1,4-dihydropyridines under steam conditions are similar to or higher than those described in the literatures. In conclusion, we have demonstrated for the first time a novel synthetic protocol enabling access to Hantzsch 1,4-DHPs in good to excellent yields in short reaction times at room temperature. We believe that the present improved modification is a convenient and attractive alternative to the existing methods for the synthesis of 1,4-DHPs.