diastereoselektiivsus

Diastereoselektiivsus describes the preference for the formation of one diastereomer over another during a chemical reaction. Diastereomers are stereoisomers that are not mirror images of each other. This means they have the same connectivity of atoms but differ in the spatial arrangement of at least two stereocenters. For instance, if a reaction can produce both *cis* and *trans* isomers of a substituted cyclobutane, and the *cis* isomer is formed in a higher yield, the reaction is diastereoselective.

This phenomenon is crucial in organic synthesis, particularly when creating molecules with multiple chiral centers. The selectivity arises from differences in the energy of transition states leading to the various diastereomers. Factors such as steric hindrance, electronic effects, and the influence of neighboring groups can direct the reaction pathway towards a specific stereoisomer. Understanding and controlling diastereoselectivity allows chemists to synthesize desired products with high purity and yield, which is often essential for the efficacy of pharmaceuticals and other fine chemicals.

Diastereoselective reactions can be classified as either diastereoselective additions, where a new stereocenter is formed, or diastereoselective eliminations, where a stereocenter is removed. The degree of selectivity is quantified by the diastereomeric excess (de), which is the difference in the percentages of the two diastereomers formed. High diastereoselectivity is a hallmark of efficient and controlled synthetic strategies.