Nickel-Catalyzed Conjugate Addition of Silyl Ketene Imines to In Situ Generated Indol-2-ones: Highly Enantioselective Construction of Vicinal All-Carbon Quaternary Stereocenters

Abstract

The first enantioselective conjugate addition of silyl ketene imines to in situ generated indol-2-ones was performed in the presence of a chiral N,N'-dioxide/Ni^II catalyst. This method provides efficient access to chiral β-alkyl nitriles bearing congested vicinal all-carbon quaternary stereocenters in up to 90 % yield with 23:1 d.r. and 98 % ee. The products enable facile transformations to chiral pyrroloindoline frameworks and spirocyclohexane oxindole derivatives. A possible transition state was also proposed to explain the origin of the asymmetric induction.

Keywords: 3-bromooxindoles; asymmetric catalysis; conjugate addition; quaternary stereocenters; silyl ketene imines.