Visible Light-Driven Azidation/Difunctionalization of Vinyl Arenes with Azidobenziodoxole under Copper Catalysis

Visible light-driven azidation of vinyl arenes with azidobenziodoxole as the azidating agent was investigated in acetonitrile by using Cu(I)(phenanthroline)(2) complex [Cu(dap)(2)]PF6 as photocatalyst. The reactions generated three types of difunctionalization products, which correspond to reaction patterns of amido-azidation, benzoyloxy-azidation, and diazidation. The electronic nature of the aryl group attached to the olefin moiety was found to play a crucial role in determining the reaction consequence: when the aryl group was electron-rich, the reactions afforded benzoyloxy-azidation products exclusively; for highly electron-deficient vinyl arenes, by contrast, diazidation products were generated in moderate yields. When the aryl group was moderately electron-rich or electron-deficient, on the other hand, a three-component reaction involving acetonitrile as well as azidobenziodoxole took place to give predominantly amido-azidation products. A plausible mechanism is proposed based on the mechanistic studies to rationalize these results. The reactions of electronically less biased vinyl arenes probably proceed via a redox catalysis pathway, while the electron-rich alkenes are believed to be converted through a radical chain process. The present reactions may be of synthetic usefulness as they provide a new means for the amido-azidation of vinyl arenes.