Silica and alumina modified by Lewis acids as catalysts in Diels-Alder reactions of carbonyl-containing dienophiles

Several aluminium and titanium derivatives are supported on silica and alumina. Some of the solids obtained contain strong Lewis acids sites and are efficient catalysts in Diels-Alder reactions of carbonyl-containing dienophiles. In cyclopentadiene reactions, high conversions and endo/exo selectivities are obtained in short reaction times, without excess of diene and with a small amount of catalyst at room temperature. With less reactive dienes, temperature, diene proportion and reaction times must be increased. However, high regio and endo/exo selectivities are obtained. The catalyst obtained by treatment of silica with diethyl aluminium chloride retains a great deal of its catalytic activity when recovered or stored in the open air for one month.This work was made possible by the generous financial support of the C.I.C.Y.T. (Project MAT90-0778-CO2-01). We are also indebted to the Subdireccion General de Cooperacion International (Accion Integrada Hispano-Francesa 243B)Peer reviewe