Enolaatit

Enolaatit, in English enolates, are the conjugate bases of carbonyl compounds formed by deprotonation at the alpha carbon of aldehydes, ketones, esters, and amides. They are widely used as reactive intermediates in organic synthesis for carbon–carbon bond formation.

In solution, enolates exist as resonance hybrids in which the negative charge is delocalized between the alpha carbon and the carbonyl oxygen. The metal counterion, typically lithium or sodium, stabilizes the enolate as a metal enolate, influencing reactivity and selectivity. Enolates can be generated in situ from carbonyl compounds using strong, non-nucleophilic bases, or isolated as metal salts. A protected form of enolates is the silyl enol ether, prepared by silylation of the corresponding enol.

Common methods for generation include using bases such as LDA (lithium diisopropylamide), NaH, KH, or organometallic reagents like n-butyllithium. These methods can favor kinetic or thermodynamic enolates: kinetic enolates form at lower temperatures with bulky, strong bases and often reside at the less substituted alpha carbon, while thermodynamic enolates form under conditions that favor the more substituted enolate.

Reactivity centers on the alpha carbon, enabling C-alkylation with alkyl halides to form new C–C bonds. Enolates also participate in classic carbonyl condensations such as aldol reactions, Dieckmann cyclizations, and Claisen condensations. O-alkylation is possible under certain conditions but C-alkylation is typically preferred for carbon skeleton construction. As masked enolates, silyl enol ethers expand the toolbox for various catalytic and stoichiometric transformations.

Enolates are foundational in modern organic synthesis, providing versatile routes to complex molecules through alpha-functionalization of carbonyl compounds.