Regioselective 1,4-hydroboration of pyridines catalyzed by an acid-initiated boronium cation.

The reaction of the commercially available ammonium salt NH4BPh4 with a pyridine-activated pinacolborane species generates a boronium cation that facilitates the 1,4-selective hydroboration of pyridines in polar solvents. This catalytic reaction is amenable to a host of reactive functional groups and provides access to sterically bulky hydroboration products, previously inaccessible by metal-free routes. Further, the regioselectivity of this reaction can be altered by reducing the polarity of the reaction solvent, resulting in greater proportions of the 1,2-hydroboration product.