A Tailored Quinoline-Locked Covalent Organic Framework for Metal-Free Photocatalytic α-Amino C–H Annulation
Jingjun Li, Jiaying Liu, Shuiying Gao, Xue Yang, Rong Cao
Abstract
Metal-free α-amino C–H annulation via photocatalysis stands as a pioneering strategy for accessing heterocyclic compounds. Imine-linked covalent organic frameworks (ILCOFs), known for their photonic excitation potential, have been underutilized in C–H annulation due to inherent photochemical instability and inefficient C–H activation. Here, we propose a novel locking strategy using chlorotrimethylsilane-catalyzed cyclization to convert ILCOF- n into stable QLCOF- n with methylquinoline motifs, thereby establishing it as a robust photocatalytic platform for metal-free α-amino C–H annulation. This structural modulation preserves crystallinity, while enhancing structural robustness and optoelectronic properties versus parent ILCOFs. QLCOF- n demonstrates superior catalytic efficiency and stability over ILCOF- n, as validated by extensive scale-up and recycling experiments, as well as substrate derivatization across 22 examples. Further investigation explores strategies to enhance the photocatalytic efficiency, including synergistic integration of film catalysis and Bro̷nsted acid (BA) assistance. The apparent quantum yield (AQY) of the film at λ = 450 nm achieves an impressive value of 1.12 ± 0.08%. Mechanistic insights highlight the pivotal roles of amino carbon and superoxide anion (O 2 •– ) radicals in the annulation. This work establishes quinoline-locked QLCOFs as durable photocatalysts for sustainable C–H functionalization.