Nano-Fe3O4 Encapsulated-Silica Particles Bearing Sulfonic Acid Groups as a Magnetically Separable Catalyst for Highly Efficient Knoevenagel Condensation and Michael Addition Reactions of Aromatic Aldehydes with 1,3-Cyclic Diketones

Sulfonic acid-functionalized silica-coated nano-Fe3O4 particles (Fe3O4@SiO2-SO3H) have been prepared as a novel heterogeneous acid using a facile process. The material was subsequently identified as an efficient catalyst for the synthesis of a variety of tetraketone derivatives via the Knoevenagel condensation and Michael addition reactions of aromatic aldehydes to dimedone, 1,3-indanedione, and 1,3-dimethyl barbituric acid. The catalyst could be readily recovered using a simple external magnet and reused several times without any significant loss in activity. The current catalytic process is both sustainable and economical because it operates under aqueous conditions, the catalyst can be recovered and reused, and the reactions themselves require only a short time and provide the products in high yield.