Regio- and Stereoselective Synthesis of Dispiro-bisoxindoles via [3+2] Annulation Involving Nitroisatylidene as a Vinylogous Michael Donor

A cascade [3+2] annulation, involving
a γ-selective vinylogous
Michael addition of nitroalkylideneoxindoles to various electron deficient
alkenes followed by an intramolecular Michael addition, provides access
to dispiro-bis-oxindoles and spiro-oxindoles. Up to four contiguous
chiral centers, including two quaternary spirocenters, are generated
in this high-yield regio- and diastereoselective transformation that
also provides a convenient entry into conformationally constrained
γ-amino acid derivatives.