Cinchona Alkaloid-derived Polymer Catalysts for Asymmetric Aza-Michael Addition of Aniline to Chalcone

Chiral cinchona alkaloid-derived polymers having cinchona squaramide repeating units showed excellent catalytic performance in the asymmetric aza-Michael reaction between aniline and chalcone. By the use of the polymer organocatalyst, chiral β-amino ketones were yielded in a highly enantioselective manner (up to >99% ee) under solvent-free conditions. The insolubility of the polymer catalyst facilitated the separation of the catalyst from the reaction mixture. The recovered polymer was reused several times without any loss of its catalytic performance. The cinchona alkaloid-derived polymers reported in this paper catalyzed an aza-Michael addition reaction more effectively than already-reported catalysts. The reaction was excellent when the squaramide-linked polymer was used under solvent-free conditions. The polymer catalyst was recoverable by an easy separation from the reaction solution and reused without loss of the catalytic performance.