The nucleophilic addition of imidazole derivatives to trifluoromethylated acetylenes was studied. Unpredictable regioselectivity of the reaction was observed to yield both β- and α-addition products. The reaction is 100% stereoselective to give the corresponding adducts as a Z -isomers only. The observed regioselectivity is discussed in terms of polarization of triple bond using experimental and calculated data.