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

With visible-light irradiation, a mild, simple, and efficient metal-free photocatalytic system for the facile construction of sp3sp3 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.