Organocatalytic Hydroboration of Carbonyl Compounds Promoted by Choline-Based Ionic Liquids

The organocatalytic
activity of choline-based ionic liquids
in
the hydroboration of ketones, aldehydes, and carboxylic acids with
pinacolborane was investigated. The employed method was based on a
simple, inexpensive, biobased, reusable, and environmentally friendly
[Cho][OAc] catalyst. Detailed studies on catalyst screening, optimization
of reaction conditions, and substrate scope were carried out. [Cho][OAc]
showed excellent tolerance to various functional groups and chemoselectivity
toward CO hydroboration, which occurred under mild conditions.
Furthermore, it was shown that the reaction can be carried out under
repetitive batch mode, allowing effective catalyst recycling and improving
the process productivity. NMR studies and quantum-mechanical calculations
based on density functional theory (DFT) were carried out to explore
the reaction mechanism.