Chapter 16: Cinchona Alkaloid Derivatives as Asymmetric Phase-transfer Catalysts

Enantioselective phase-transfer catalysis (PTC) is among the most useful asymmetric methodologies for practical syntheses, due to its operational simplicity, mild reaction conditions, environmentally friendly reaction procedure, and applicability to large-scale synthesis 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. Cinchona alkaloids have been a popular natural source of practical chiral organocatalysts due to their unique structures and commercial availability at low cost. Since the first successful application of Cinchona alkaloid-derived ammonium salts as phase-transfer catalysts in 1984, many Cinchona alkaloid derivatives have been developed and successfully applied to various asymmetric phase-transfer catalysis reactions serving as a sustainable green chemistry. In this chapter, we describe the development of Cinchona-derived chiral PTC catalysts, mainly based on asymmetric alkylation using Schiff base substrates and their applications to a variety of other enantioselective transformations.