Borane‐Catalyzed Chemoselective and Enantioselective Reduction of 2‐Vinyl‐Substituted Pyridines.

Herein, we report that highly chemoselective and enantioselective reduction of 2‐vinyl‐substituted pyridines has been achieved for the first time. The reaction, which uses chiral spiro‐bicyclic bisboranes as catalysts and HBpin and an acidic amide as reducing reagents, proceeds through a cascade process involving 1,4‐hydroboration followed by transfer hydrogenation of a dihydropyridine intermediate. The retained double bond in the reduction products permits their conversion to natural products and other useful heterocyclic compounds by simple transformations. [ABSTRACT FROM AUTHOR]