stereocontrol

Stereocontrol refers to the ability to direct the formation of specific stereoisomers in chemical reactions. It encompasses enantioselectivity, the preferential creation of one enantiomer over its mirror image, and diastereoselectivity, the preference for one diastereomer among several possibilities. Stereocontrol arises from chiral influences in the reaction system, including chiral catalysts, chiral reagents or auxiliaries, and the inherent stereochemical information present in the substrate.

Approaches to achieve stereocontrol include asymmetric catalysis, where a chiral catalyst accelerates the formation of a preferred enantiomer or diastereomer; the use of chiral auxiliaries that temporarily impose stereochemical bias on the substrate; and substrate-controlled reactions in which existing stereocenters direct the outcome of subsequent steps. Enantioselectivity is commonly quantified by the enantiomeric excess (ee), while diastereoselectivity is described by the diastereomeric ratio (dr).

Common examples of stereocontrolled methods include asymmetric hydrogenation, enantioselective aldol and Michael additions, and enantioselective epoxidations or Diels–Alder reactions. These approaches often employ metal-based catalysts (such as ruthenium, rhodium, or palladium complexes) or organocatalysts, and may rely on chiral ligands, ligands on metal centers, or chiral organocatalysts to create a stereochemical environment in the transition state.

Stereocontrol is essential in the synthesis of pharmaceuticals, natural products, and materials, where the configuration of stereocenters can determine biological activity, properties, and function.