Nanoconfined Photocatalytic Cascade Reaction in Vinylene-Linked Covalent Organic Frameworks

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.