The Disappearing Director: The Case of Directed N-Arylation via a Removable Hydroxyl Group.

A facile and broadly applicable method for the regiospecific N-arylation of benzotriazoles is reported. Copper-mediated reactions of diverse 1-hydroxy-1H-benzotriazoles with aryl boronic acids lead to 1-aryl-1H-benzotriazole 3-oxides. A N1-OH → N3 prototropy in the 1-hydroxy-1H-benzotriazoles is plausibly the underlying basis, where the tautomer is captured by the boronic acid, leading to C-N (not C-O) bond formation. Because the N-O bond in amine N-oxides and 1-hydroxy-1H-benzotriazoles can be easily reduced by diboron reagents such as (pinB)2 and B2(OH)4, exposure of the 1-aryl-1H-benzotriazole 3-oxides to B2(OH)4 then leads to facile reduction of the N-O bond resulting in diverse, regiospecifically-arylated benzotriazoles. Thus, the N-hydroxyl group in 1-hydroxy-1H-benzotriazoles acts as a disposable arylation director.