BF3-promoted aromatic substitution of N-alkyl α-trifluoromethylated imine:: Facile synthesis of 1-aryl-2,2,2-trifluoroethylamines

The aromatic substitution of three representative N-alkyl trifluoromethyl imines 1a-c (R: a, benzyl; b, benzhydryl; c, methyl), obtained from primary alkyl amines and trifluoroacetaldehyde ethyl hermacetal, was used to investigate the preparation of 1-aryl-2,2,2-trifluoroethylamines. In the presence of BF3-OEt2, the reaction of imine 1 with various aromatic compounds proceeded smoothly at room temperature, giving N-alkyl-1-aryl-2,2,2-trifluoroethylamines in moderate-to-high yields. Moreover, successful regioselective removal of N-benzyl and N-benzhydryl groups was achieved by hydrolysis in hydrochloric acid or by palladium-catalyzed hydrogenolysis.