A metal-free methodology for the
photoarylation of pyridines, in
water, is described giving 2 and 4-arylated-pyridines in yields up
to 96%. The scope of the aryldiazonium salts is presented showing
important results depending on the nature and position of the substituent
group in the diazonium salt, that is, electron-donating or electron-withdrawing
in the ortho, meta, or para positions. Further heteroaromatics were also successfully photoarylated.
Mechanistic studies and comparison between our methodology and similar
metal-catalyzed procedures are presented, suggesting the occurrence
of a visible-light EDA complex which generates the aryl radical with
no need for an additional photocatalyst.