Preparation of magnetic particles modified with calixarenes and evaluation as catalyst in Biginelli reaction

Dihydropyrimidinones (DHPMs) are obtained from the Biginelli reaction, requiring acid catalysts to increase the yield. The p-sulfonic acid calix[4]arene has already been used, in homogeneous medium, in this reaction [1]. However, solid catalysts have many advantages over homogeneous catalysts. Thus, systems that can use this acid supported on a solid can be an important alternative for the synthesis of DHPMs [2]. The use of magnetic particles as supports of catalyst unites the efficiency of a heterogeneous catalyst to its magnetic capacity [3]. In this context, the synthesis of the DHPMs was carried out using the magnetic particles modified with calixarenes, according to Scheme 1. The reaction conditions were optimized (temperature, solvent, catalyst) and shown in Scheme 1. Then, different aromatic aldehydes were tested, and yields ranged from 55-88%. The catalyst maintained its constant activity after five cycles of reuse (80-88% yield). The next steps will be to apply the catalyst to other multicomponent reactions and glycerol valuation reactions.