Copper-Catalyzed\nDefluorinative [3 + 2] Cyclization\nof Amidines and Trifluoromethyl Carbenoids for the Synthesis of 5‑Fluoroimidazoles

A Cu-catalyzed [3 + 2] cyclization of amidines with trifluoromethyldiazo\ncompounds is described. The reaction affords 5-fluoroimidazoles in\ngood yields by cleaving dual C–F bonds in a CF<sub>3</sub> group.\nUsing 2-aminoazo heterocycles as the substrates, various annelated\nimidazoles containing a fluorine atom were also constructed by this\nmethod without changing the conditions. The resultant 5-fluoroimidazoles\nshow high reactivity toward S<sub>N</sub>Ar reactions with a series\nof nucleophiles.