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.