Visible Light Photoredox Catalyzed Biaryl Synthesis
Using Nitrogen Heterocycles as Promoter
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Abstract
Although
transition-metal-catalyzed direct arylation of aromatic
C–H bonds is one of the most efficient ways for the construction
of biaryl targets, it is also expected for other alternative methods
that can use inexpensive catalysts and abundant solar energy to drive
chemical reactions. Herein, we describe a new activation mode for
biaryl synthesis by using a photosensitive complex of potassium <i>tert</i>-butoxide (KO<i>t</i>-Bu) and nitrogenous
heterocyclic ligands via visible light excitation. Under low-energy
visible light irradiation, the single-electron transfer from electron-donor
KO<i>t</i>-Bu to electron-deficient nitrogenous heterocycle
occurred in the inner part of the complex by using potassium as a
bridge atom. The ligand accepted the as-photoexcited single electron
and transformed into stable radical anions which played a dominant
role in the coupling reactions of benzene with aryl halides at ambient
temperature. This reaction paradigm features the use of inexpensive
catalyst, abundant visible light energy, and more accessible bromobenzene
for the construction of biaryl compounds under rather mild conditions