Enantioselective Cascade Reactions under N-Heterocyclic Carbene Catalysis

The use of chiral N-heterocyclic carbenes (NHCs) as catalysts in asymmetric synthesis has opened a wide range of applications due to their unique ability to generate reaction intermediates with unusual reactivity patterns that very often involve the reversal of the typical polarity associated with the functional groups present in the starting materials. In this sense, the direct activation of aldehydes or surrogates by these reactive species provides different chemical structures (conjugated Breslow intermediates, azolium enolates and dienolates, or unsaturated acyl azolium cations) which constitute excellent platforms for initiating cascade or domino reactions in the presence of a polyfunctional reagent. 1 Introduction 2 Cascade Reactions Initiated by the Participation of Homoenolate Equivalents 3 Cascade Reactions Initiated by the Participation of Azolium Enolates 4 Cascade Reactions Initiated by the Participation of Dienolate Equivalents 5 Cascade Reactions Initiated by the Participation of alpha ,beta-Unsaturated Acyl Azolium Intermediates 6 Summary and Outlook