Quaternary ammonium salts, especially derived from Cinchona Alkaloids, have become the most privileged class of chiral PTCs.

Asymmetric PTC has been recognized as a “green” alternative to many homogeneous synthetic organic transformations and is nowadays one of the major catalytic principles in the synthesis of chiral molecules.

Its operational simplicity, mild reaction conditions, environmentally friendly reaction procedure, ready availability, easy recovery / reuse and the low toxicity of these catalysts makes it applicable to large-scale synthesis of complex and multi-functionalized organic molecules in industrial processes. In particular, the use of water as a solvent, heavy transition metal-free conditions, and low energy consumption due to employing room temperature or 0 °C as the reaction temperature make phase-transfer catalysis suitable as a sustainable green chemistry.