Transition-Metal-Catalyzed Allylic Substitution Reactions: Stereoselective Construction of α- and β-Substituted Carbonyl Compounds

Abstract

The stereoselective synthesis of α- and β-substituted carbonyl compounds remains a significant area of interest in organic chemistry. This is largely due to their ubiquity and versatility as synthetic intermediates and the importance of this functionality in a range of biologically important agents. In this context, the transition-metal-catalyzed allylic substitution provides an extremely powerful tool for the asymmetric construction of a variety of α- and β-tertiary and quaternary substituted carbonyl compounds. This review highlights pertinent historical developments of these reactions, from the seminal work with enolate equivalents to the more recent developments with unstabilized enolates and acyl anions. It also outlines the most important mechanistic aspects of these transformations in order to provide insight into the current scope and limitations and potential areas for further development. 1 Introduction 2 Unstabilized Enolate Nucleophiles 2.1 Enolate Equivalents 2.1.1 Enamines 2.1.2 Imines 2.1.3 Silyl Enol Ethers 2.1.4 Enolstannanes 2.1.5 Decarboxylative Approaches 2.2 Metal Enolates 2.2.1 Boron Enolates 2.2.2 Tin Enolates 2.2.3 Copper Enolates 2.2.4 Zinc Enolates 2.2.5 Magnesium Enolates 2.2.6 Sodium Enolates 2.2.7 Lithium Enolates 3 Acyl Anion Equivalents 3.1 Acylmetal Nucleophiles 3.2 ‘Masked’ Acyl Anion Equivalents 4 Conclusions