Synthesis of Chiral Trispirocyclic Oxindoles via Organic-Base/Au(I)-Catalyzed Sequential Reactions

Chiral
spirooxindole is the core structure of a large number of
natural and unnatural products with biological activities. However,
the construction of trispirocyclic oxindoles remains challenging because
of the difficulty in the assembly, the complex skeleton, and control
of the stereoselectivities of the multiple quaternary stereocenters.
Herein, we present the organic base/Au­(I)-catalyzed sequential asymmetric
1,2-addition/cascade hydroamination/HDA/deisobutene reactions for
the elaboration of various trispirocyclic N,O-ketal tethered oxindoles and bisoxindoles in excellent
optical purities (91–99% ee). Key to the success
of this methodology is Au­(I)-catalyzed hetero-Diels–Alder reactions
utilizing N-Boc-iminooxindoles as the heterodienes.