Copper-Catalyzed Defluorinative [3 + 2] Cyclization of Amidines and Trifluoromethyl Carbenoids for the Synthesis of 5-Fluoroimidazoles

A Cu-catalyzed [3 + 2] cyclization of amidines with trifluoromethyldiazo compounds is described. The reaction affords 5-fluoroimidazoles in good yields by cleaving dual C–F bonds in a CF3 group. Using 2-aminoazo heterocycles as the substrates, various annelated imidazoles containing a fluorine atom were also constructed by this method without changing the conditions. The resultant 5-fluoroimidazoles show high reactivity toward SNAr reactions with a series of nucleophiles.