Ionic Liquid Effect in Catalysed Multicomponent Reactions
In this book chapter the effects produced in using ionic liquids over multicomponent reactions are presented and discussed. Ionic liquids may be used as reaction media (solvents) or as catalysts for several multicomponent reactions. It is observed that many multicomponent reactions characteristically proceed through charged intermediates, thereby rendering them as desirable features to interact with cations and/or anions of ionic liquids. These interactions are mostly ruled by Coulombic attraction/stabilisation between the charged intermediates and the ionic liquid ions. These Coulombic interactions give rise to new ion pairs and larger supramolecular aggregates (higher ion clusters). Additional interactions such as hydrogen bonds and van der Waals forces also play a role in the formation, directionality (entropic drivers) and stabilisation of these ion pairs (and larger supramolecular clusters) between the charged intermediates and the ionic liquid ions; an effect typically noted for imidazolium derivatives. Understanding the multicomponent reaction mechanism in this context is essential in aiming at predicting a positive ionic liquid effect. Many multicomponent reactions have proven to be capable of undergoing two or more competitive reaction mechanisms, but usually the final multicomponent reaction adduct is the same regardless of the reaction pathway. Ionic liquids may also contribute to tune the reaction through one specific mechanism. As we intend to show herein, the combination of multicomponent reactions and ionic liquids typically returns excellent results and produces many achievements, although both are a huge challenge to understand and to predict their effects over multicomponent reactions.