Visible-light-initiated catalyst-free oxidative cleavage of (Z)-triaryl-substituted alkenes containing pyridyl motif under ambient conditions

Abstract

The catalyst-free oxidative cleavage of (Z)-triaryl-substituted alkenes bearing a pyridyl motif in ambient air under the irradiation of blue LEDs at room temperature has been developed. The reaction was facile and scalable, and proceeded with good functional group tolerance, affording pharmaceutically useful 2-acyl pyridines. The electron paramagnetic resonance (EPR) studies together with control experiments showed that the singlet oxygen (¹O₂) and superoxide anion (O₂˙⁻) are the reactive oxidants. The ¹O₂ generation mechanism correlated well with the photophysical properties of the substrate (Z)-triaryl-substituted alkenes, the excited state of which was proved to serve as the triplet sensitizer for the generation of ¹O₂.