Metal-Free Perfluoroarylation by Visible Light Photoredox Catalysis

Visible light and eosin Y catalyze
the direct arylation of simple
arenes with fluorinated aryl bromides by a photoredox process. The
reaction scope is broad in fluorinated compounds and arenes and the
general and simple procedure provides a metal-free alternative for
the synthesis of synthetically valuable polyfluorinated biaryl structures.
The mild reaction conditions allow a selective reaction with the alkaloid
brucine without protection of functional groups illustrating the potential
of the process for late stage functionalization. Mechanistic investigations
reveal the photoreduction of eosin Y via its triplet state by triethylamine
and subsequent electron transfer from the eosin Y radical anion to
the polyfluorinated bromoarene, which fragments into the polyfluorinated
aryl radical and a bromide anion. A radical chain reaction mechanism
was excluded by a quenching factor analysis.