Memory of chirality: An emerging strategy for asymmetric synthesis

'Memory of chirality' (MOC) is an intriguing strategy for asymmetric synthesis because it appears to do the impossible: the sole chiral center of a molecule directs the stereochemical course of a reaction even though that center is destroyed in the key reactive inter-mediate. This review describes the critical role of transient conformational chirality in these processes, and defines the three essential requirements for success in an MOC method. The growing application of MOC to asymmetric synthesis methodology is discussed, with extensive coverage of enolate, radical, photochemical and carbocation reactions. 1 Introduction 1.1 Requirements for Memory of Chirality 1.2 Dynamic Chirality 2 Memory of Chirality in Enolate Chemistry 2.1 alpha-Alkylation of an Aspartic Acid Ester Enolate 2.2 Designed Asymmetric Alkylation of a Naphthyl Ketone 2.3 Enantioselective alpha-Alkylation of Amino Acid Esters without External Chiral Sources 2.4 Enantioselective Synthesis of Azacyclic Amino Acids 2.5 Proposed Mechanism of Asymmetric Induction in Deprotonation/Alkylation of Amino Acid Esters 2.6 Other Cyclization Reactions Involving Axially Chiral Enolate Intermediates 2.7 Enantioselective Synthesis of Quaternary 1,4-Benzodiazepine-2-ones 3 Memory of Chirality in Radical Chemistry 3.1 Retentive Benzylic Substitution Induced by Dynamic Planar Chirality 3.2 Retentive Radical Trapping Controlled by a Slow Ring Inversion 3.3 Memory of Chirality in Radical Cyclization 3.4 Memory of Chirality in the Cyclization of Photochemically Generated Diradicals 4 Memory of Chirality Involving Carbocation Intermediates 5 Conclusion