Recent advances in carbon–carbon bond-forming reactions involving homoenolates generated by NHC catalysis

TLDR: The versatility of NHC-bound homoenolate is illustrated by its annulation with various carbonyl compounds leading to gamma-butyrolactones, spiro-gamma- butyrolactsones, and delta-lactones.

Abstract: Homoenolate, a species containing anionic carbon β to a carbonyl group or a moiety that can be transformed into a carbonyl group, is a potential three carbon synthon. Recent introduction of a protocol for the generation of homoenolate directly from enals by NHC (nucleophilic heterocyclic carbene) catalysis has made it possible to explore the synthetic utility of this unique reactive intermediate. The versatility of NHC-bound homoenolate is illustrated by its annulation with various carbonyl compounds leading to γ-butyrolactones, spiro-γ-butyrolactones, and δ-lactones. Interception of homoenolate with imines afforded γ-lactams and bicyclic β-lactams. Formation of cyclopentenes and spirocyclopentanones respectively by reaction with enones and dienones is also noteworthy. This tutorial review focuses on these and other types of reactions which attest to the synthetic potential of NHC-bound homoenolates in organic synthesis.