abstract
- Nanoconfined catalysis and cascade reactions taking place in two-dimensional covalent organic frameworks (2D-COFs) hold great promise for tackling the long-standing challenges such as uncontrollable reactive intermediates and low selectivity in aerobic oxidation. Herein, for the first time, a nanoconfined photocatalytic cascade reaction system based on vinylene-linked nitrogen-rich 2D-COFs (N-2D-COFs) have been developed for selective generating oxazole derivatives which are privileged building blocks for numerous natural products and bioactive molecules. The CSU-4N-COF photocatalyst enables in itu H2O2 generation as needed, and achieves a remarkable yield (> 90%), high selectivity (> 98%) and robust reusability (> 7 consecutive runs) under mild conditions for oxidative cyclization of N-propargyl amides. This performance rivals leading-edge photocatalytic systems and significantly surpasses other COFs analogs, comparable to the current industrial route. Both experimental study and theoretical calculation confirm that the nanoconfinement effect of vinylene-linked N-2D-COFs enables a precise regulation on adsorption and transformation of Se-based reactive species (PhSeOOH), while simultaneously suppressing competitive side reactions like coupling of reactive radicals (PhSeOO•). This work systematically elucidates the critical role of nanoconfinement effect in modulating behaviors of intermediates for advancing aerobic oxidation, and also provides new insight for engineering high-performance COF photocatalysts.