Improved process for implementing the Diels-Alder reaction that consists in using reagents in the presence of at least one liquid salt of general formula Q.sup.+ A.sup.-, in which Q.sup.+ represents a quaternary ammonium and/or phosphonium and A.sup.- represents an anion and optionally at least one Lewis acid. The anion is preferably selected from the group that is formed by tetrafluoroborate, hexafluorophosphate, hexafluoroantimonate, hexafluoroarsenate, perfluoroalkylsulfonate, fluorosulfonate or else dichlorocuprate, tetrachloroborate, tetrachloroaluminate, and trichlorozincate. At the end of the reaction, the organic phase is separated, and the polar phase is reused.