The Disappearing Director: The Case of Directed <i>N</i>‐Arylation <i>via</i> a Removable Hydroxyl Group

Abstract

A facile and broadly applicable method for the regiospecific <i>N</i>-arylation of benzotriazoles is reported. Copper-mediated reactions of diverse 1-hydroxy-1<i>H</i>-benzotriazoles with aryl boronic acids lead to 1-aryl-1<i>H</i>-benzotriazole 3-oxides. A <i>N</i>1-OH → <i>N</i>3 prototropy in the 1-hydroxy-1<i>H</i>-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 <i>N</i>-oxides and 1-hydroxy-1<i>H</i>-benzotriazoles can be easily reduced by diboron reagents such as (pinB)₂ and B₂(OH)₄, exposure of the 1-aryl-1<i>H</i>-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 <i>N</i>-hydroxyl group in 1-hydroxy-1<i>H</i>-benzotriazoles acts as a disposable arylation director.