Abstract: A method is disclosed for the pretreatment of olefinic hydrocarbon feedstock to remove conjugated dienes and/or basic nitrogen compounds that deactivate acidic catalyst particles used in olefin conversion processes by reacting the dienes with one or more dienophiles to form the corresponding Diels-Alder adduct, followed by catalytic conversion of the olefinic hydrocarbon feedstock containing the adduct. The formation of the Diels-Alder adduct essentially eliminates the role of dienes in the feedstock as catalyst deactivating agents. When maleic anhydride (MA) is employed as the dienophile, basic nitrogen reacts with maleic anhydride, or with the tetrahydrophthalic anhydride adduct, to lower the amount of catalyst deactivating basic nitrogen compounds in the feedstock. Where the olefin conversion process comprises etherification of isoolefins with alkanol in a C.sub.4 + or C.sub.