Activation Modes in Asymmetric Anion-Binding Catalysis

Abstract Over the past two decades, enantioselective anion-binding catalysis has emerged as a powerful strategy for the induction of chirality in organic transformations. The stereoselectivity is achieved in a range of different reactions by using non-covalent interactions between a chiral catalyst and an ionic substrate or intermediate, and subsequent formation of a chiral contact ion pair upon anion binding. This strategy offers vast possibilities in catalysis and the constant development of new reactions has led to various substrate activation approaches. This review provides an overview on the different activation modes in asymmetric anion-binding catalysis by looking at representative examples and recent advances made in this field. 1 Introduction 2 Electrophile Activation by Single Anion-Binding Catalysis 2.1 Prior In Situ Charged Electrophiles 2.2 Neutral Electrophile Activation via Anion Abstraction 2.2.1 Anion Abstraction via an SN1 Mechanism 2.2.2 Anion Abstraction via an SN2 Mechanism 3 Nucleophile Activation and Delivery 4 Bifunctional and Cooperative Co-catalysis Strategies 4.1 Amine Groups for Bifunctional and Cooperative Catalysis 4.2 Brønsted Acid Co-catalysis 4.3 Lewis Acid Co-catalysis 4.4 Lewis Base Co-catalysis 4.5 Nucleophilic Co-catalysis for Activation of Electrophiles 4.6 Cooperative Metal and Anion-Binding Catalysis 4.7 Combination of Photoredox and Anion-Binding Catalysis 5 Anion-π Catalysis 6 Conclusion