Recyclable C2-symmetric tertiary amine-squaramide organocatalysts: Design and application to asymmetric synthesis of γ-nitrocarbonyl compounds

Abstract

Simple C2-symmetric chiral tertiary amines bearing squaramide fragments along with the 1,2-di(pyridin-2-yl)ethane spacer group have been synthesized. Among them, amine 8b with a different configuration of stereocenters in 1,2-di(pyridin-2-yl)ethane and 1,2-diaminocyclohexane units efficiently catalyzed asymmetric additions of β-dicarbonyl compounds to nitroolefins and domino reaction of ortho-(tosylamino)chalcone with β-nitrostyrene in wet (20 equiv. of H2O) DCM, affording corresponding adducts in up to 99% yield and 94% ee. The developed procedure is scalable. Due to poor solubility in organic solvents and water, the catalyst could be readily separated from the reaction mixture and over 10 times reused in the reaction without compromising enantiomeric enrichment and yield of product.