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.