HClO 4–SiO 2 and PPA–SiO 2 catalyzed efficient one-pot Knoevenagel condensation, Michael addition and cyclo-dehydration of dimedone and aldehydes in acetonitrile, aqueous and solvent free conditions: Scope and limitations

Abstract

Efficient one-pot Knoevenagel condensation, Michael addition and cyclodehydration of dimedone with various aldehydes in acetonitrile and solvent free conditions using PPA–SiO 2 catalyst gave 1,8-dioxo-octahydroxanthenes 3 in excellent yields; whereas in the presence of HClO 4–SiO 2 catalyst the reaction is limited to give only 2,2′-arylmethylene bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-1-one) 4 in very good yields. In aqueous medium both HClO 4–SiO 2 and PPA–SiO 2 catalysts yielded only 4 as the product. The scope and limitations of the two catalysts in various reaction conditions examined were described.