Selective C(sp 2 )-H Halogenation of "Click" 4-Aryl-1,2,3-triazoles.

Selective bromination reactions of "click compounds" are described. Electron-neutral and electron-deficient arenes selectively undergo unprecedented Pd-catalyzed C-H ortho-halogenations assisted by simple triazoles as modular directing groups, whereas electron-rich arenes are regioselectively halogenated following an electrophilic aromatic substitution reaction pathway. These C-H halogenation procedures exhibit a wide group tolerance, complement existing bromination procedures, and represent versatile synthetic tools of utmost importance for the late-stage diversification of "click compounds". The characterization of a triazole-containing palladacycle and density functional theory studies supported the mechanism proposal.