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-1 H -benzotriazoles with aryl boronic acids lead to 1-aryl-1 H -benzotriazole 3-oxides. A N 1-OH → N 3 prototropy in the 1-hydroxy-1 H -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-1 H -benzotriazoles can be easily reduced by diboron reagents such as (pinB)2 and B2 (OH)4 , exposure of the 1-aryl-1 H -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-1 H -benzotriazoles acts as a disposable arylation director.