Stereoselective Synthesis of Tetrahydroquinolines via Asymmetric Domino Reaction Catalyzed by a Recyclable Ionic-Liquid-Supported Bifunctional Tertiary Amine

The most recyclable ionic liquid-supported bifunctional tertiary amine-squaramide organocatalyst for the asymmetric domino reaction has been found. Over this catalyst, ortho-aminochalcones protected with Tosyl or Nosyl groups underwent the aza-Michael/Michael domino reaction with nitroolefins to afford corresponding 2,3,4-trisubstituted tetrahydroquinolines as single diastereomers in nearly quantitative yield with up to 99 % ee. The catalyst was readily separated from the reaction mixture via a simple centrifugation/decantation workup and 19 times reused in the catalytic reaction without noticeable conversion or enantioselectivity reduction. The N-nosylated products proved their synthetic value for pharmacology given their facile conversion to fused pirrolidino-tetrahydroquinolines of high diastreomeric and enantiomeric purity via successive deprotection and reductive amination.