HClO4-SiO2 and PPA-SiO2 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

Efficient one-pot Knoevenagel condensation, Michael addition and cyclodehydration of dimedone with various aldehydes in acetonitrile and solvent free conditions using PPA-SiO2 catalyst gave 1,8-dioxo-octahydroxanthenes 3 in excellent yields; whereas in the presence of HClO4-SiO2 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 HClO4-SiO2 and PPA-SiO2, catalysts yielded only 4 as the product. The scope and limitations of the two catalysts in various reaction conditions examined were described. (c) 2007 Elsevier B.V. All rights reserved.