In the case that the substrate is constituted by olefins, these can be represented by the following formula: ##STR1## in which R5, R6, R7 and R8, which may also be substituted with functional groups inert under the reaction conditions, indifferently represent hydrogen atoms or hydrocarbyl moieties, such as alkyl and alkenyl radicals of up to 30 carbon atoms, cycloalkyl and cycloalkenyl radicals of