Ligand-Controlled Chromium Catalysis for Tunable Z/E Selectivity in Asymmetric Homoallylic Alcohol Synthesis

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.