Enantiomerically Pure Amines as Substrates for the Ti‐Catalyzed Hydroamination of Alkynes

For two representative reactions employing enantiomerically pure (S)‐1‐phenylethylamine and (S)‐1‐cyclohexylethylamine it is shown that Ti‐catalyzed hydroamination reactions of alkynes do not generally take place without partial racemization 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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)