Memory of chirality: An emerging strategy for asymmetric synthesis

摘要

'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 Introduction1.1 Requirements for Memory of Chirality1.2 Dynamic Chirality2 Memory of Chirality in Enolate Chemistry2.1 alpha-Alkylation of an Aspartic Acid Ester Enolate2.2 Designed Asymmetric Alkylation of a Naphthyl Ketone2.3 Enantioselective alpha-Alkylation of Amino Acid Esters without External Chiral Sources2.4 Enantioselective Synthesis of Azacyclic Amino Acids2.5 Proposed Mechanism of Asymmetric Induction in Deprotonation/Alkylation of Amino Acid Esters2.6 Other Cyclization Reactions Involving Axially Chiral Enolate Intermediates2.7 Enantioselective Synthesis of Quaternary 1,4-Benzodiazepine-2-ones3 Memory of Chirality in Radical Chemistry3.1 Retentive Benzylic Substitution Induced by Dynamic Planar Chirality3.2 Retentive Radical Trapping Controlled by a Slow Ring Inversion3.3 Memory of Chirality in Radical Cyclization3.4 Memory of Chirality in the Cyclization of Photochemically Generated Diradicals4 Memory of Chirality Involving Carbocation Intermediates5 Conclusion