Reactivity and Mechanistic Insight into Visible‐Light‐Induced Aerobic Cross‐Dehydrogenative Coupling Reaction by Organophotocatalysts

Abstract

With visible‐light irradiation, a mild, simple, and efficient metal‐free photocatalytic system for the facile construction of sp³–sp³ 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 (O₂^−.) rather than singlet oxygen (¹O₂) during visible‐light irradiation. This active species is therefore believed to be responsible for the large rate of acceleration of the aerobic photocatalytic reactions.