关键词: 二苯并[b;d]氮杂䓬-6-酮, 磺酰化, 多样官能化, 可见光催化, 7-exo-trig自由基环化

This study presents a photoinduced 7-exo-trig radical cyclization protocol for the efficient synthesis of diversely functionalized dibenzo[b,d]azepin-6-ones. Characterized by mild reaction conditions, broad substrate scope, and excellent functional group tolerance, this method enables the direct construction of various 7-substituted derivatives, with sulfonylated compounds emerging as the predominant product class. Notably, the protocol is not limited to sulfonyl-based radical precursors; a variety of other radical sources were also successfully employed to introduce diverse functional groups at the 7-position. Radical trapping experiments, Stern-Volmer fluorescence quenching studies, and light on/off experiments were performed to elucidate the reaction mechanism. The results indicate that the reaction is initiated by single-electron transfer between the excited-state Ir(III) species and arylsulfonyl chloride, generating a sulfonyl radical that adds to the alkene substrate. Density functional theory (DFT) calculations reveal that methyl-substituted alkenes fail to undergo cyclization due to a significantly elevated activation barrier (23.3 kcal/mol for TS_Me vs 18.4 kcal/mol for TS_H), which accounts for the observed substituent-dependent chemoselectivity. This protocol provides a practical alternative to traditional transition-metal-catalyzed C-H activation/cyclization strategies for constructing this important heterocyclic scaffold. Collectively, this strategy offers a concise and robust synthetic platform for accessing biologically relevant dibenzo[b,d]azepin-6-one scaffolds with potential biological activities. The general procedure is as follows: to a mixture of N-aryl acrylamide substrates (0.2 mmol), arylsulfonyl chloride (0.3 mmol, 1.5 equiv.), and Ir(ppy)₃ (2 mol%) in a 10 mL Schlenk tube was added acetonitrile (3.0 mL). The vessel was evacuated and backfilled with N₂ three times. The tube was screw-capped and stirred at room temperature under irradiation of 24V blue LEDs (λmax = 455 nm, distance ca. 5-6 cm) for 2 hours. After completion of the reaction, the mixture was concentrated under reduced pressure, and the residue was purified by flash column chromatography on silica gel using a mixture of petroleum ether and ethyl acetate (V_PE:V_EA = 3:1) as the eluent to afford the desired products.

Key words: Dibenzo[b,d]azepin-6-ones, sulfonylated, diversely functionalized, visible-light-induced, 7-exo-trig radical cyclization