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

摘要

src="http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ascecg/2017/ascecg.2017.5.issue-11/acssuschemeng.7b02613/20171031/images/medium/sc-2017-02613u_0012.gif">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 β-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.