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.