High-Efficient Photocatalytic Synthesis of Tetrahydroquinolines Featuring Cu/Zr Metal-Organic Frameworks

Tetrahydroquinolines (THQs) are essential scaffolds in natural products and pharmaceutical agents, and feasible synthetic assembly strategies for them remain highly desirable. Photocatalysis presents an ecofriendly and atom-utilizing pathway for obtaining THQs; however, the development of high-performance photocatalysts for this transformation is still a formidable task. Here, we introduce Cu@NU-1000, a defect-engineered photocatalyst fabricated by embedding copper species into the secondary building units (SBUs) of Zr-based metal-organic framework (MOF) NU-1000. Introducing copper species alters the electronic structure of NU-1000, thereby facilitating charge redistribution and enhancing electron-hole separation. In addition, the inherent structural characteristics of MOFs, such as high porosity and large specific surface area, further promote selective substrate adsorption and activation. The Cu/Zr centers and pyrene linkers act synergistically as dual active sites, significantly enhancing the catalytic activity of Cu@NU-1000. The resulting photocatalytic system exhibits a broad substrate scope and remarkable efficiency, enabling the synthesis of THQs in yields as high as 94% with a significantly reduced catalyst loading. Furthermore, this catalytic system achieves remarkable recyclability over at least five cycles. This research not only presents a strong approach to enhance the photocatalytic efficiency of the materials but also creates a versatile platform for the mild and sustainable photoproduction of THQs derivatives.