(Thio)urea and Squaramide‐Catalyzed Anion‐Binding Catalysis with Halogen Anions

This chapter describes the development of anion-binding catalysis using halogen anions, beginning with the foundational work on which this catalytic manifold is building. The evolution of this approach to asymmetric synthesis is discussed with examples relying on noncovalent interactions between organocatalysts and electrophiles. Reactions utilizing N -acyliminiums, as well as other electrophile types, are described in detail from a physical organic chemistry perspective. Asymmetric catalytic methods using catalyst association with the nucleophile through hydrogen-bonding motifs are also presented.