New Developments in Stereoselective Palladium-Catalyzed Allylic Alkylations of Preformed Enolates

Whereas the enantioselective palladium-catalyzed allylic substitution with ʹsoftʹ, stabilized carbanions can be considered as established and versatile method today, nonstabilized, preformed enolates were used for this purpose only very reluctantly. This ­report focuses on progress made recently in combining (pi)-allyl ­palladium complexes with different metal enolates derived from carboxylic esters and ketones. The elaboration of protocols that ­permit enantioselective and - at the same time - diastereoselective allylic alkylations are emphasized in this report. The stereochemistry in the approach of the enolate to the (pi)-allyl palladium complex is also discussed. 1 Introduction 2 Palladium-Catalyzed Allylic Alkylations with Different Metal Enolates 2.1 The Role of Preformed Enolates 2.2 Silyl Enol Ethers and Silyl Ketene Acetals 2.3 Tin and Boron Enolates and their ʹAteʹ Complexes 2.4 Zinc Enolates 2.5 Lithium and Magnesium Enolates 2.6 Enolates Generated in situ 3 Mechanistic Aspects 4 Conclusion