Diastereoselective Electrophile‐Directed Alkylations

Abstract

Electrophile‐directed alkylations in which a chiral, sp3‐hybridized electrophile, dictates the facial attack on a prochiral nucleophile, provides a powerful method of asymmetric induction. The strategy is inherently efficient because the asymmetry of an sp3‐hybridized electrophile is propagated to install two contiguous chiral centers, the first through an SN2 displacement and the second through preferential facial recognition. The two primary modes of topological matching are through steric approach control and chelation between the electrophile and nucleophile. Electrophiles capable of chelation generally induce higher diastereoselectivity for secondary and primary electrophiles. Key parameters that influence the stereoselectivity are those expected for enolate/anion alkylations: solvent, cation, complexing agents. A generalized enolate‐electrophile alkylation model is used to provide an evaluative framework for collecting related alkylations with the aim of providing insight into the origin of the electrophile‐directed diastereoselectivity as a powerful synthetic strategy.