Chapter 25: Alkylation of Enolates

The authors present both kinetic and thermodynamic enolates, emphasizing how reaction conditions such as base strength, temperature, and solvent determine which enolate isomer predominates and how this selectivity impacts alkylation outcomes. A central focus involves regioselectivity in unsymmetrical carbonyl compounds, where competition between monoalkylation and polyalkylation must be carefully controlled through stoichiometry and base choice. The chapter details how different bases like lithium diisopropylamide produce kinetic enolates preferentially at less-substituted positions, while other conditions favor thermodynamic enolates at more-substituted alpha carbons. The authors thoroughly discuss mechanistic pathways, including SN2 and SN1 processes depending on the alkylating agent structure and reaction conditions. Stereochemical considerations are addressed, particularly how enolate geometry and alkylating agent approach determine stereochemical outcomes in subsequent transformations. The chapter also covers malonic ester alkylations and related synthetic protocols that leverage enolate reactivity for efficient carbon skeleton construction. Particular attention is given to controlling unwanted side reactions such as polyalkylation through protecting group strategies and alternative synthetic routes. The relationship between enolate structure, reactivity, and selectivity provides predictive frameworks for designing alkylation sequences in multi-step synthesis. Applications in synthesizing natural products and pharmaceutical intermediates demonstrate the practical importance of mastering enolate alkylation in modern organic chemistry.