A dual-engineered covalent organic framework with charge-oxygen synergy promotes photocatalytic dipolar [3 + 2] cycloaddition

The photocatalytic oxidative dipolar [3 + 2] cycloaddition reaction is a promising green approach for producing pyrrolo[2,1-<i>a</i>]isoquinolines. However, developing sustainable cycloaddition methods with heterogeneous photocatalysts is still in its infancy, largely owing to their low reactivity and photostability. Herein, we propose a charge-oxygen synergy strategy through a dual-engineered covalent organic framework (COF) by integrating π-spacers with donor-acceptor motifs to promote intermolecular cycloaddition. Systematic analyses reveal that electron-deficient thiadiazole units significantly enhance exciton dissociation efficiency, while a fully conjugated acetenyl spacer promotes spontaneous oxygen adsorption to stabilize endoperoxide intermediate species. This synergistic interplay between charge separation and oxygen activation significantly boosts reactive oxygen species generation, enabling efficient C-H bond activation under visible light. Remarkably, the BTDE-COF efficiently promotes dipolar [3 + 2] cycloaddition, achieving up to 97.1% yield with a broad substrate scope under visible light irradiation, while enabling a gram-scale synthesis. This work suggests that strategically engineering COFs has the potential to foster a variety of visible light-mediated energy-transfer processes.