New Approach for Complete Reversal of Enantioselectivity Using a Single Chiral Source

Abstract

Obtaining both enantiomers of a given compound in high enantiomericexcess is an attractive and important challenge, because it is oftenthe case that each enantiomer exhibits different bioactivity. Thisreview summarizes some approaches to realize complete reversal ofenantioselectivity by changing various reaction conditions. Ournew approach to achieve reversal of enantioselection in the enantioselectiveaddition of diketene to aldehydes, affording optically active 5-hydroxy-3-ketoesters in high optical yield using Schiff bases that contain anoxazoline moiety derived from L-serine,is also described. 1 Introduction 2 Reversal Based on the Nature of the Substituent 2.1 Control with Catalyst Substituent 2.2 Control with Substrate Substituent 3 Control with Central Metal 4 Reversal of Enantioselectivity by Changing Reaction Conditions 4.1 Control with Solvent 4.2 Control with Temperature 4.3 Control with Additives 4.4 Control with Other Factors 5 Recent Concepts for Reversal of Enantioselectivity 5.1 Asymmetric Addition of Readily Available Nucleophiles withAldehydes 5.2 Enantioselectivity Reversal in Asymmetric Addition of Diketenewith Aldehydes 6 Conclusions and Outlook