Asymmetric Catalysis. The field of asymmetric catalysis has revolutionized organic synthesis in the last 50 years. Catalysts have been developed to introduce stereogenic centers into molecules primarily through the formation of new C-C bonds and reduction of unsaturated bonds (e.g., carbonyls, alkenes). These chiral catalysts can take many forms, including transition metal complexes, organocatalysts, and biocatalysts (Figure ). With transition metal complexes, the reaction is often catalyzed by the metal itself while stereochemistry is introduced in the form of metal ligands (e.g., chiral phosphines). In organocatalysis and biocatalysis, small organic molecules and enzymes function as both catalysts and chiral directing groups.