Multi-component Syntheses of Diverse 5-Fluoroalkyl-1,2,3-Triazoles Facilitated by the Air Oxidation and Copper catalysis
Air is the ideal oxidant due to its abundance, low cost and lack of toxic by-products. However, catalytic aerobic oxidation reaction using air as the oxidant is still challenging due to reduced activity and poor selectivity. In this paper, a new class of glycinamide-type ligands were sucessfully synthesized and utilized to aerobic oxidative reaction through the in-situ trapping of formed triazolides with nucleophilic fluoroalkyl reagents. By this designed oxidative procedure, variant 5-fluoroalkyl-1,2,3-triazoles could be synthesized from avaible fluoroalkyl reagents, terminal alkynes and organic azides through the one-pot reactions. Air was used as the sole oxidant, which is greatly reduced the cost of this transfermation and the resulted operations and work-up procedures were greatly simplified. Alkyl azides and alkynes bearing various functional groups and nature structural motifs, and even aryl azides that are ineffective in other reported methods, reacted efficiently under the current conditions. Different fluoroalkyl reagents including trifluoromethyl trimethylsilane (CF3TMS), pentafluoroethyl trimethylsilane (C2F5TMS) and heptafluoropropyltrimethylsilane (C3F7TMS) could be used effectively for the reactions. Mechanism study further indicated that the new N,O-ligand could stabilize Cu(I) catalyst in a multiple binding mode and effectively promote the generation of oxidative coupling products. High efficiency together with a wider substrate scope enlisted this copper-catalyzed aerobic coupling reaction among the most efficient methods for preparations of 5-fluoroalkyl 1,2,3-triazoles.