Ligand‐Controlled Chromium Catalysis for Tunable <i>Z</i> / <i>E</i> Selectivity in Asymmetric Homoallylic Alcohol Synthesis

Abstract

Abstract Chiral homoallylic alcohols with vicinal stereocenters and well‐defined Z/E alkene geometries are key structural motifs in bioactive polyketides, yet their efficient and selective synthesis remains a long‐standing challenge in asymmetric catalysis. Existing strategies often require preformed organometallic reagents or separate catalytic systems to access different alkene geometries, limiting synthetic efficiency and versatility. Herein, we report a chromium‐catalyzed asymmetric reductive coupling of allyl gem ‐dichlorides with aldehydes, enabling precise and tunable control over regio‐, enantio‐, diastereo‐, and Z/E ‐selectivity. This radical‐polar crossover strategy circumvents the need for preformed organometallic reagents, offering a direct and modular approach to stereochemically complex homoallylic alcohols. A chiral imidazoline sulfonamide ligand directs the formation of Z ‐alkenes, while a bisoxazoline ligand reverses the selectivity to E ‐alkenes, achieving excellent stereocontrol across a broad substrate scope. Mechanistic studies support a chromium‐mediated allyl radical generation and addition pathway. This work establishes a versatile platform for constructing stereochemically defined homoallylic alcohols and expands the synthetic utility of allyl gem ‐dichlorides in asymmetric catalysis.