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

Abstract

Whereas the enantioselective palladium-catalyzed allylic substitution with ‘soft’, 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 π-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 π-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 ‘Ate’ Complexes

• 2.4 Zinc Enolates

• 2.5 Lithium and Magnesium Enolates

• 2.6 Enolates Generated in situ

• 3 Mechanistic Aspects

• 4 Conclusion

Key words

chirality - catalysis - substitution - carbon-carbon bond formation - asymmetric synthesis

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62

The face selectivity of the cyclohexanone enolate is relatively low when compared with the corresponding reaction of diphenyl-substituted acetate 58. This may indicate that the remote phenyl group has a significant influence on stereoselectivity.

63

Braun, M.; Meier, T. Synthesis, to be submitted.