Water-soluble (salicyladimine)<sub>2</sub>Cu complex as an efficient and renewable catalyst for Michael addition of indoles to nitroolefins in water

<p>An efficient and environmentally friendly protocol has been demonstrated for water-soluble (salicyladimine)<sub>2</sub>Cu complex-catalyzed Michael addition of indoles to nitroolefins in water at 30 °C. A variety of substituted indoles and β-nitrostyrenes could be worked well to provide the title products in 81–97% yields. Moreover, the catalyst can be reused directly at least for four times without significantly decreasing activity.</p>