Synthesis of Fluorinated 1,4,5-Substituted 1,2,3-Triazoles by RuAAC Reaction

Herein, we report a convenient methodology for the synthesis of fluorinated 1,4,5-substituted 1,2,3-triazoles. The azide-alkyne cycloaddition reaction of internal alkynes catalyzed by a ruthenium complex efficiently afforded 2,2,2-trifluoroethyl- and (trifluoromethyl)thio-substituted 1,2,3-triazoles. Two types of internal alkyne, 1-aryl-2-(2,2,2-trifluoroethyl)acetylenes and 1-aryl-2-[(trifluoromethyl)thio]acetylenes, were used. This ruthenium-catalyzed azide-alkyne cycloaddition reaction was highly regioselective giving 4-aryl-5-(2,2,2-trifluoroethyl)- or 4-aryl-5-[(trifluoromethyl)thio]-1H-1,2,3-triazoles. Various functionalities were tolerated in the alkyl and aryl azides by this Huisgen 1,3-dipolar cycloaddition. All the triazoles were characterized by H-1, C-13, and F-19 NMR, IR, and HRMS (or elemental analysis). Several triazoles were characterized by single-crystal X-ray structural analysis to confirm the regioselectivity of 1,2,3-triazole formation.