关键词: 可见光诱导反应, 吲哚-2-酮, 芳基卤化物, N-芳基丙烯酰胺, 无催化剂合成

Oxindoles constitute privileged heterocyclic scaffolds frequently encountered in natural products, pharmaceuticals, and other biologically active compounds. Herein, we disclose an operationally simple, visible-light-driven arylative cyclization of N-arylacrylamides with aryl halides, providing rapid access to structurally diverse 3,3-disubstituted oxindoles without transition metals or exogenous photocatalysts. Under the optimized conditions, an N-arylacrylamide, an aryl halide, and diisopropylethylamine (DIPEA) are dissolved in dimethyl sulfoxide and irradiated with 18 W violet light-emitting diodes at room temperature for 20 h. Unlike established approaches that rely on metal catalysts, photocatalysts, or additional activating reagents, this protocol uses readily available aryl halides as aryl radical precursors and proceeds under additive-free conditions. The method accommodates a range of substituents on the N-aryl moiety and the aryl halide coupling partner, demonstrating good functional-group tolerance and enabling the preparation of various oxindole derivatives. The method's synthetic practicality is further supported by successful gram-scale synthesis. Control experiments establish that both light and DIPEA are indispensable for productive conversion. The reaction proceeds efficiently under nitrogen but is almost completely suppressed by oxygen. Furthermore, addition of 2,2,6,6-tetramethylpiperidin-1-oxyl inhibits cyclization, indicating the involvement of radical intermediates. Light on/off experiments reveal that product formation occurs only during irradiation and ceases in the dark, confirming the essential role of continuous illumination. Based on these observations, we propose a plausible pathway involving photoinduced activation of the carbon-halogen bond and formation of an aryl radical. Regioselective radical addition to the acrylamide, followed by intramolecular cyclization, oxidation, and deprotonation, furnishes the desired oxindole. Overall, this catalyst-free transformation combines mild conditions, broad substrate compatibility, scalability, and reduced reagent requirements, thus providing a practical and sustainable route to valuable oxindole scaffolds. Nevertheless, the limited reactivity of less activated coupling partners remains to be addressed.

Key words: Visible-light-induced reaction, Oxindoles, Aryl halides, N-Arylacrylamides, Catalyst-free synthesis