Chiral Bicyclic Guanidine, Bis-Guanidinium, Pentanidium and Related Organocatalysts

The roles of chiral bicyclic guanidine, bis-guanidinium and pentanidium in catalysis are presented. Besides the usual Bronsted base reactivity, less known modes of interactions of these catalysts, such as Bronsted base–Bronsted acid and Bronsted–Lewis acid bifunctional activations will be discussed in this account. Pentanidiums are ‘super-guanidines’ with extended conjugation, and their roles in catalysis and halogen bonding will also be elaborated.