Stereogenic centers free radical reaction

Numerous research groups have shown that chiral auxiliaries can be used in free-radical reactions for the generation of new stereogenic centers [34], Sibi and Yamamoto have used oxazolidinone chiral auxiliaries in the presence of bidentate Lewis acid to create bicyclic intermediates and control the outcome of reactions (Scheme 11). 

A substitution reaction at a stereogenic center can lead to a racemic mixture of products. For example, in the free radical reaction of bromine with (5) l-chloro-2-methylbutane, a bromine atom replaces a hydrogen atom at the tertiary stereogenic center to give a racemic mixture of R) and (5)-2-bromo-l-chloro-2-methylbutane. 

The formation of new stereogenic centers using chemical intermediates such as free radicals, carbanions, or carbocations can be influenced by many factors such as solvents, electronic effects, the electrophilicity or nucleophilicity of reagents, and the presence of Lewis acid. Of course, the intrinsic reactivity of the intermediate used will also affect the outcome of the reaction. Still, the general principles governing the induction of diastereoselectivity remain the same for all of the above-mentioned species. 

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