Hollow CuO-CeO2 Nanospheres for an Effectively Catalytic Annulation/A3-Coupling Reaction Sequence

A heterogeneous catalyst CuO-CeO2 with a hollow structure was successfully synthesized by assembling CuO on the outer surface of CeO2 hollow spheres through a layer-by-layer deposition strategy. Further reduction under a H-2 atmosphere was carried out to modify its surface state, resulting in sample r-CuO-CeO2. The catalysts were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform-infrared spectroscopy (FT-IR). SEM and TEM showed that the synthesized catalysts had a hollow sphere structure, which can expose more active sites and promote mass transfer. The results of XPS revealed that the content of Cu-0 & Cu+ increased from 13.6 to 19.0% after H-2 reduction, which was conducive to the activation of terminal alkyne to promote the annulation/A3-coupling reaction. The conversion of this cascade reaction with the r-CuO-CeO2 catalyst can reach more than 95%, while the value was only 55% by using CuO-CeO2 as a catalyst. Moreover, the r-CuO-CeO2 catalyst showed a good recycle property and group compatibility in the general applicability of the cascade annulation/A(3)-coupling reaction, providing a series of propargylamine derivatives in good chemoselectivity.