Asymmetric catalysis is a method of achieving asymmetric synthesis by using a chiral catalyst. Chiral catalysts are catalysts containing chiral C atoms, which play a pivotal role in some synthetic reactions. Asymmetric synthesis, also known as chiral synthesis, stereoselective synthesis, and enantioselective synthesis, is an organic synthesis branch that studies the chemical reaction of introducing one or more chiral elements into a reactant. According to the definition of Morrison and Mosher, asymmetric synthesis is "an organic reaction in which an achiral unit in the bulk of a substrate molecule is converted into a chiral unit by a reactant that produces a stereoisomer in an unequal amount." Here, the reactant can be a catalyst, a chemical reagent, a solvent or a physical factor. Asymmetric organocatalysts are catalysts that catalyze an asymmetric organic reaction.
Asymmetric organocatalysts are generally stable in nature, cheap and readily available, non-toxic, and have asymmetric synthetic potentials for chiral activity. The types of asymmetric organocatalysts are extremely diverse. According to the type of reaction, they can be divided into asymmetric catalytic hydrogenation organocatalysts, asymmetric catalytic oxidation organocatalysts, non-dihydroxylation organocatalysts, asymmetric hydroxylation organocatalysts, asymmetric catalytic cyclopropanation organocatalysts, and asymmetric hydrocyanide organocatalysts.
Asymmetric organocatalysts have a wide range of applications in the synthesis field, and one of the most common applications is to catalyze the Michael addition reaction. The Michael addition reaction is one of the easiest ways to construct a C-C bond, through which many important intermediates can be synthesized. In addition, there are asymmetric catalytic hydrogenation reactions, asymmetric catalytic oxidation reactions, asymmetric catalytic carbonyl reduction reactions and so on.
Figure 1. L-valine catalyzed asymmetric Michael addition reaction