Reactivity and mechanistic insight into visible-light-induced aerobic cross-dehydrogenative coupling reaction by organophotocatalysts

摘要

With visible-light irradiation, a mild, simple, and efficient metal-free photocatalytic system for the facile construction of sp ~3-sp ~3 C-C bonds between tertiary amines and activated C-H bonds has been achieved. Spectroscopic study and product analysis demonstrate for the first time that photoinduced electron transfer from N-aryl tetrahydroisoquinolines to eosin Y bis(tetrabutylammonium salt) (TBA-eosin Y) takes place to generate TBA-eosin Y radical anion, which can subsequently react with nucleophiles and molecular oxygen. More strikingly, electron spin resonance (ESR) measurements provide direct evidence for the formation of superoxide radical anions (O_2 ?) rather than singlet oxygen (~1O_2) during visible-light irradiation. This active species is therefore believed to be responsible for the large rate of acceleration of the aerobic photocatalytic reactions. Light work: With visible-light irradiation (λ>450 nm), a mild, simple and efficient metal-free photocatalytic system for the facile construction of sp ~3-sp ~3 C-C bonds between tertiary amines and activated C-H bonds has been achieved (see scheme). Electron spin resonance measurements offer direct evidence for the formation of superoxide radical anions (O_2 ?) during visible-light irradiation.