Copper(II) Schiff-Base Complex Modified UiO-66-NH2(Zr) Metal–Organic Framework Catalysts for Knoevenagel Condensation–Michael Addition–Cyclization Reactions

The synthesis of five- and six-membered oxygen- and nitrogen-containing heterocycles has been regarded as the most fundamental issue in organic chemistry and chemical industry because they are used in producing high-value products. In this study, an efficient, economic, sustainable, and green protocol for multicomponent synthesis has been developed. The one-pot direct Knoevenagel condensation-Michael addition-cyclization sequences for the transformation of aromatic aldehydes, malononitrile, and 4-hydroxycoumarin or phthalhydrazide generate the corresponding dihydropyrano[2,3-c]chromenes and 1H-pyrazolo[1,2-b]phthalazine-5,10-diones over a novel mesoporous metal-organic framework-based supported Cu(II) nanocatalyst [UiO-66@Schiff-Base-Cu(II)] under ambient conditions. Moreover, the [UiO-66@Schiff-Base-Cu(II)] complex efficiently catalyzed the selectively large-scale synthesis of the target molecules with high yield and large turnover numbers. As presented, the catalyst demonstrates excellent reusability and stability and can be recycled up to six runs without noticeable loss of activity. Moreover, ICP-AES analysis showed that no leaching of Cu complex occurred during the recycling process of the heterogeneous [UiO-66@Schiff-Base-Cu(II)] nanocatalyst.