Cinchona Alkaloids in Organic Catalysis
Durch Katalysatoren bewirkte asymmetrische Synthese.
Biochem. Z. 1912;
Asymmetrische Synthesen mit Ketenen.
Justus Liebigs Ann. Chem. 1960;
15. April 2019 (online)
In 1912, Bredig and Fiske published the first example of asymmetric (nonenzymatic) (organo)catalysis. They reported the addition of HCN to benzaldehyde catalyzed by the pseudoenantiomeric alkaloids quinine and quinidine, with low but reproducible enantioselectivities. About four decades later, Pracejus, for the first time, achieved reasonable enantioselectivities (74% ee) by using O-acetylquinine as an organocatalyst. This groundwork paved the way to a variety of cinchona-alkaloid-catalyzed asymmetric transformations in industry and academia.
Cinchona alkaloids are among the most privileged asymmetry inducers in the area of enantioselective catalysis. They possess a chiral skeleton that is easily modifiable. In the last century, methodologies were developed in which they were used as chiral bases, as chiral Lewis base catalysts, in ligand-accelerated catalysis, or as quaternized ammonium salts in phase-transfer catalysis, among others. Current research continues to showcase their importance and utility in asymmetric catalysis, for example by incorporating other privileged organic catalophores such as thioureas.