CHAPTER 5. Anion–π Catalysis

The anion–π interaction is nowadays considered as a consolidated member of the supramolecular weak interactions family. In its naissance, it was mostly used in host–guest chemistry for the molecular recognition of anions. Nowadays its application to the construction of functional systems is attracting considerable attention. In this context, the anion–π interaction has become a prominent player in noncovalent catalysis since anionic intermediates can be conveniently stabilized on π-acidic surfaces. Remarkably, examples embrace enolate, enamine and iminium chemistry, domino processes and Diels–Alder reactions. Moreover, it is worth highlighting the recent appearance in the literature of the first example of asymmetric anion–π catalysis of cascade reactions that afford nonadjacent stereocentres. The anion–π catalysts are usually constructed using naphthalenediimide and/or fullerene building blocks, which present extended π-acidic surfaces along with high polarizabilities and are thus well suited for establishing anion–π interactions. In this chapter, we review the general concept of anion–π catalysis. It is based on the stabilization of anionic transition states and intermediates by anion–π interactions on π-acidic aromatic surfaces. Since 2013, anion–π catalysis has been explored with several reactions. In addition, anion–π enzymes and electric field-assisted anion–π catalysis are also described.