Cobalt-Catalyzed Asymmetric Sequential Hydroboration/Hydrogenation of Internal Alkynes

A highly regio- and enantioselective
cobalt-catalyzed hydroboration/hydrogenation
of internal alkynes with HBpin and a hydrogen balloon in one pot was
developed. A new type of chiral imidazoline iminopyridine (IIP) ligand
was introduced for the first time in this novel and efficient strategy.
This protocol used relatively simple and available starting materials
with good functional group tolerance to construct more valuable chiral
secondary organoboronates. The primary mechanistic studies illustrated
that the cobalt-catalyzed regioselective hydroboration of alkynes
did initially occur followed by HBpin-promoted and cobalt-catalyzed
enantioselective hydrogenation of alkenylboronates.