[3+2]-cycloaddition reactions of α-trifluoromethyl imino esters with nitrile Imines: Construction of penta-substituted 5-CF3-1,2,4-triazolines

An efficient [3 + 2]-cycloaddition reaction between α-trifluoromethyl imino esters and di/trifluoromethyl nitrile imines or nonfluorinated nitrile imines generated in-situ from hydrazonoyl halides in the presence of base has been investigated, affording a series of fluoroalkylated penta-substituted 1,2,4-triazolines with a quaternary C5 carbon atom in high yields with excellent regioselectivity under mild conditions. The results show that α-trifluoromethyl imino esters could serve as outstanding dipolarophiles suitable for [3 + 2]-cycloadditions with various fluorinated or non-fluorinated nitrile imines.