Iridium-Catalyzed Asymmetric Hydrogenation of N-Protected Indoles

Chiral indolines substituted at C-2 or C-3 can be prepared in high yield and excellent enantioselectivity by asymmetric hydrogenation of N-protected indoles by using Ir catalysts with chiral N,P ligands. With less reactive substrates, the reaction had to be carried out at elevated temperature, but even at 60–110 °C very high enantiomeric excesses of up to 98–99 % could be obtained.