Asymmetric induction (also enantioinduction) in stereochemistry describes the preferential formation in a chemical reaction of one enantiomer or diastereoisomer over the other as a result of the influence of a chiral feature present in the substrate, reagent, catalyst or environment.
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- Diastereofacial selection in nucleophilic additions to acyclic aldehydes and ketones is of major importance in synthetic organic chemistry. … In 1952, Donald I. Cram (1919-2001, Nobel Prize in Chemistry, 1987) and his coworker Fathy A. Abd Elhafez presented an experimental rule for the diastereoface-differentiating reaction of ketones having a chiral center at the vicinal carbon with metal hydride complexes or with organometallic reagents. … The Cram rule as originally formulated is only valid when there is no chelating group attached to the substrate and so neglects any dipolar interactions with the nucleophile. Moreover, there is considerable torsional strain between the L and the R groups. … The degree of Cram and Felkin-Anh selectivity depends on a number of other factors. … α-Chelation not only increases the electrophilic character of the carbonyl carbon but also prevents free rotation about the Cα-C(=O) bond, thus directing the nucleophile to the less hindered Si diastereoface. … these 1,2- asymmetric inductions in such rigid chelated systems provide a high degree of diastereoselectivity.
- George S. Zweifel and Michael H. Nantz, Modern Organic Synthesis (2006), Ch. 4 : Functional Group Transformations: Oxidation and Reduction