Ionic Liquid-coordinated Ytterbium(III) Sulfonate Catalyzed Michael Addition of Indoles to Electron-deficient Nitroolefins

The Michael addition of indoles to electron-deficient nitroolefins was effectively catalyzed by an ionic liquid-coordinated ytterbium(III) sulfonate catalyst. The recycling procedure of the catalyst was very simple without extraction with water, and the catalyst was reused for five times without any loss of its catalytic activity. Furthermore, to demonstrate the application of this methodology, the Pictet-Spengler reaction was chosen and successfully carried out in the mixture of Bronsted-acidic ionic liquid and [bmim]BF(4).