Enantio- and Diastereoselective Diverse Alkylation of Homoenolates via Bifunctional <i>N</i> -Heterocyclic Carbenes

We report a chiral bifunctional N-heterocyclic carbene (NHC) catalyst that enables enantio- and diastereoselective alkylation of homoenolates. Quantitative steric maps (%Vbur) of the catalytic pocket explain stereocontrol and guide catalyst optimization for metal-free SN2 alkylations with unactivated and bulky secondary halides (>20:1 dr, up to 99% ee)─a significant advance in homoenolate reactivity. The method’s usefulness is demonstrated through short syntheses of bioactive targets, including (+)-coerulescine, pyrroloindolines, and CRTH2 receptor antagonists, using a modular, transient acyl-trapping strategy. Mechanistic studies show a dynamic kinetic resolution (DKR) pathway and confirm the importance of noncovalent interactions in stereoselectivity. Additionally, the chiral NHC allows the isolation and X-ray crystallographic analysis of a stable triazolium-derived homoenolate intermediate, providing direct structural insight into a longstanding challenge in NHC catalysis. By linking homoenolate structure to reactivity, this work creates a framework for rational NHC catalyst design in stereoselective transformations.