Enantiomerically pure amines as substrates for the Ti-catalyzed hydroamination of alkynes

For two representative reactions employing enantiomerically pure (S)-1-phenylethylamine and (S)-l-cyclohexylethylamine it is shown that Ti-catalyzed hydroamination reactions of alkynes do not generally take place without partial race-mization at the chiral center adjacent to the nitrogen atom. However, identified from a selection of nine Ti catalysts, CP*2TiMe2 and at least two other catalysts can be used for racemization-free hydroamination reactions of alkynes. Furthermore, the amount of racemization can be reduced significantly by the addition of pyridine to the reaction mixture. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).