homoenolate

Homoenolate, also called gamma-enolate or vinylogous enolate, refers to the enolate equivalent formed when deprotonation occurs at the gamma position of a carbonyl compound. This places the reactive center one carbon farther from the carbonyl than in a conventional enolate and generates an extended, conjugated anionic system in which the negative charge can be delocalized across the carbonyl and the gamma-carbon region. The resulting species behaves as a nucleophile at the gamma center.

Generation and scope: Homoenolates are typically generated from β,γ-unsaturated carbonyl compounds (such as enones, esters, or 1,3-dicarbonyls) by deprotonation at the gamma position using strong bases or through other activation strategies that reveal the gamma-functionalized form. In some systems the homoenolate is accessed as a distinct intermediate, while in others it is invoked conceptually as the gamma-extended form of an enolate in catalytic or ionic processes.

Reactivity and applications: The gamma-centered nucleophile can undergo gamma-alkylation with electrophiles, enabling C–C bond formation at the gamma position. It can also participate in intramolecular cyclizations to form rings and in various cross-coupling or condensation processes. Collectively, these transformations are referred to as homoenolate chemistry and are used to construct carbon frameworks adjacent to carbonyl groups.

Relationship to related concepts: Homoenolates are related to vinylogous enolates, with terminology and emphasis varying by substrate and conditions. The concept broadens the synthetic toolkit for forming bonds beyond the alpha position of carbonyls and is employed in both classical and modern asymmetric synthesis.