This work presents a catalyst-free, visible-light-driven protocol for constructing biologically relevant oxindoles via intramolecular hydroarylation of N-arylacrylamides, mediated by in situ-generated electron donor-acceptor (EDA) complexes. Diverging from conventional transition-metal catalysis or oxidative cyclization, which require metal pre-catalysts, pre-functionalized substrates, or strong oxidants, this strategy operates without external photocatalysts, acids, or chemical oxidants. Central to the mechanism is the weak base (Cs₂CO₃)-promoted hydrolysis of diphenyl disulfide (PhSSPh), which generates phenylthiolate anions (PhS^－) as potent electron donors. Mechanistic studies, including comprehensive UV-Vis spectroscopy, establish that these PhS^－ anions form a photoactive EDA complex with electron-deficient N-arylacrylamides (acceptors). Critically, this complex exhibits a distinct broad absorption band (450~500 nm), enabling direct visible-light irradiation (455~460 nm) to trigger single-electron transfer (SET) and initiate radical cyclization. Deuterium-labeling experiments (D₂O) confirm that trace water serves as the proton source in the reaction, while radical trapping studies corroborate the radical nature of the pathway. Substrate scope evaluation (33 diverse examples) demonstrates broad functional group tolerance on the aryl ring, accommodating both electron-donating (para-methyl, para-methoxy) and electron-withdrawing (para-halogen, trifluoromethyl, cyano, ester) substituents, as well as heterocyclic motifs (pyridyl). Ortho-substituted arenes cyclize with reduced efficiency due to steric hindrance, while meta-methyl substitution yields α/β-regioisomers. Diverse N-alkyl groups (isopropyl, cyclohexyl), functionalized N-substituents (benzyl, ester), and conformationally constrained diamides are compatible, highlighting versatility. A key limitation is the inactivity of free N-H acrylamides under the current conditions, suggesting the N-substituent is crucial for EDA complex formation or reactivity. Significant advantages of this strategy include operational simplicity (ambient temperature, 16 h reaction time), avoidance of precious metals and stoichiometric oxidants, demonstrated gram-scale feasibility, and the utilization of benign visible light. By leveraging the unique electron-donating capability of in situ-generated sulfur anions (PhS^－) to form catalytically active EDA complexes, this work provides a green, practical, and mechanistically distinct route to privileged oxindole scaffolds.

Key words: visible-light induction, oxindole, electron donor-acceptor (EDA) complex, N-arylacrylamide, catalyst-free synthesis