What do we know about the ionic liquid effect in catalyzed multicomponent reactions?: A critical review

Several multicomponent reactions (MCRs) have been conducted with improved yields and selectivities when ionic liquids (ILs) were applied as the catalysts or reaction media, as will be presented and discussed in this tutorial review. The current review also presents the importance of the IL effect in catalyzed MCRs. The effect of ion-pairing formation of large supramolecular aggregates, as well as their influences on the outcome of MCRs, are analyzed. Far beyond a reaction media of “innocent” ionic components, ILs are capable of aiding in the formation, stabilization and to improve the reactivity of reagents and intermediates during a multicomponent transformation. The origin of these positive effects relies on a combined action of cations and anions during the reaction. Although enantioselective MCRs are rarely carried out in ILs, they are also presented and critically analyzed.