enolatos

An enolate, or enolate ion, is the conjugate base of an enol, formed by deprotonation at the alpha position of a carbonyl compound such as a ketone, aldehyde, or ester. The negative charge is delocalized over the alpha carbon and the carbonyl oxygen, giving resonance forms that stabilize the anion. Enolates act as nucleophiles at the alpha carbon and, in some cases, as ambident nucleophiles that can react through carbon or oxygen.

Enolates can be generated under basic conditions or prepared as protected enolates. Common methods use strong bases such as LDA, NaH, or NaNH2 to generate metal enolates (lithium, sodium, or potassium) or to form silyl enol ethers by silylation. Kinetic enolates (less substituted) form with bulky, cold bases, while thermodynamic enolates (more substituted) form under warmer conditions with smaller bases. Some enolates are ambident, tending to react at carbon or oxygen depending on conditions, solvents, and electrophiles.

Silyl enol ethers are a widely used class of enolate equivalents, prepared by treating a carbonyl compound with a silyl chloride (for example, TMSCl) in the presence of a base. They participate in a broad range of carbon–carbon bond-forming reactions, including Mukaiyama aldol reactions, and can be revealed to carbonyl compounds under acidic or fluoride-rich conditions.

Applications of enolate chemistry include alpha-alkylation and acylation of carbonyl compounds, aldol reactions, Claisen condensations, and Michael additions. Enolates enable formation of complex molecules via controlled C–C bond formation and are central to many synthetic strategies in organic chemistry.