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Synthesis of cinchona alkaloid squaramide polymers as bifunctional chiral organocatalysts for the enantioselective michael addition of β-ketoesters to nitroolefins

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Abstract Novel chiral polymers containing cinchona-based squaramides in their main chain structure were designed. We synthesized chiral squaramides bearing two cinchona moieties, which contain double bonds. Repeated Mizoroki-Heck reactions between… Click to show full abstract

Abstract Novel chiral polymers containing cinchona-based squaramides in their main chain structure were designed. We synthesized chiral squaramides bearing two cinchona moieties, which contain double bonds. Repeated Mizoroki-Heck reactions between the double bonds of the cinchona-based squaramide and aromatic diiodides proceeded smoothly to give cinchona squaramide chiral polymers. The catalytic activity of the chiral polymers was subsequently investigated. The asymmetric Michael addition of β-ketoesters to nitroolefins was successfully catalyzed by the polymeric organocatalysts to give the corresponding Michael adducts in good yields and excellent enantioselectivities of up to 99% ee . As the polymeric catalysts were insoluble in commonly used organic solvents, they were easily recovered from the reaction mixture and reused for further reaction without any loss of catalytic activity.

Keywords: michael addition; ketoesters nitroolefins; addition ketoesters; cinchona; chiral polymers

Journal Title: Molecular Catalysis
Year Published: 2017

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