Electrophilic substitution of indole with trifluoroacetaldehyde hemiaminals 1a-f, prepared from primary amines and trifluoroacetaldehyde ethyl hemiacetal (TFAE), proceeds readily in the presence of Lewis acids. Formation of N-alkyl 1-(indol-3-yl)-2,2,2-trifluoroethylamines (2) is preferred in the presence of BF 3 , but yield of 2,2,2-trifluoroethyl alcohol (3) markedly increases when ZnI 2 is used. A stereochemistry study clearly showed that ethylamines 2e and 2f are produced with high diastereoselective excess when the optically active hemiaminals 1e and 1f are used.