Confined N‐oxyl Radical as a Redox Shuttle Enabling the Efficient Benzoxazole Synthesis Under Visible Light With TiO 2 and TEMPO
Hao Li, Ting Li, Kaiyi Su, Jinlan Cheng, Tingwei Zhang, Zhengwei Li, Chengyan Zou, Hanlian Chen, Jingjing Yang, Chaofeng ZhangABSTRACT
The integration of semiconductor photocatalysis with molecular redox catalysis offers an attractive strategy for developing efficient synthetic methodologies. Herein, a heterogeneous–homogeneous hybrid catalytic system based on TiO 2 , N‐hydroxyphthalimide (NHPI), and 2,2,6,6‐tetramethylpiperidine‐1oxyl (TEMPO) is developed for the visible‐light‐driven synthesis of benzoxazoles from 2‐aminophenols and aldehydes. Upon adsorption on the TiO 2 (anatase) surface, NHPI is proposed to undergo a ligand‐to‐metal charge transfer (LMCT) process under blue LED irradiation, generating surface‐confined phthalimide‐N‐oxyl radicals (PINO•). These confined PINO• radicals are proposed to act as redox shuttles between TiO 2 and the TEMPO/TEMPOH cycle, enabling efficient activation of ArO─H and C─H bonds under mild conditions. Mechanistic studies suggest that the reaction likely proceeds via radical coupling between a phenoxyl radical and an imine intermediate, followed by oxidative dehydrogenation to afford benzoxazoles. This work provides an effective strategy for integrating semiconductor photocatalysis with radical‐mediated transformations, thereby expanding the application of semiconductor materials in organic synthesis.