Chiral 2-Aminobenzimidazoles in Deep Eutectic Mixtures: Recyclable Organocatalysts for the Enantioselective Michael Addition of 1,3-Dicarbonyl Compounds to β-Nitroalkenes

A catalytic system based on deep eutectic solvents (DESs) and chiral 2-amino benzimidazole organocatalysts is used to promote the enantioselective addition of 1,3-dicarbonyl compounds to beta-nitrostyrenes. This procedure avoids the use of toxic volitile organic compounds (VOCs) as a reaction medium, providing access to highly functionalized chiral molecules in a selective and efficient manner. Furthermore, the reaction can be performed on a large scale and recycling the catalytic system is possible for at least four times, leading to a clean, cheap, simple, and scalable procedure that meets most of the criteria required to be a green and sustainable process. Nuclear magnetic resonance studies have confirmed the key role of the hydrogen bonding interactions between the DES and the chiral organocatalyst, which allow their recovery and the recyclability of the system.