enolateequivalent

An enolate equivalent is a reagent or surrogate that behaves like an enolate, enabling α-carbon nucleophilicity and carbon–carbon bond formation without the need to generate a free enolate by strong base deprotonation. Enolate equivalents provide a flexible approach to alpha-alkylation, acylation, and aldol-type reactions under milder conditions or with greater functional-group tolerance than direct enolate formation. They are often masked or prefunctionalized forms that release true enolate reactivity under activation by acids, bases, or catalysts.

Common families of enolate equivalents include:

- Enamines: formed from carbonyl compounds and secondary amines; they act as nucleophiles at the α-carbon toward electrophiles and are converted back to carbonyl compounds by hydrolysis (the Stork enamine strategy).

- Silyl enol ethers: prepared from ketones or aldehydes; under Lewis acid catalysis they behave as α-nucleophiles in Mukaiyama-type aldol and related reactions.

- Boron enolates: boron-stabilized enolate equivalents used in asymmetric aldol reactions with high stereocontrol.

- Silyl ketene acetals (SKAs): act as masked enolates enabling various acylation and alkylation reactions.

- Enol phosphates and related masked enolates: serve in diverse electrophilic additions and rearrangements.

Enolate equivalents are chosen for factors such as reactivity, stereochemical outcomes, substrate scope, and catalyst compatibility. They enable synthesis of β-hydroxy carbonyls, α-alkylated carbonyl compounds, and other α-functionalized frameworks without handling highly basic conditions or unstable enolates. See also enolate chemistry and enamine chemistry for related masked-enolate strategies.