Effective and diastereoselective preparation of dispiro[cyclopent-3'-ene]bisoxindoles via novel [3+2] annulation of isoindigos and MBH carbonates

A novel and diastereoselective [3 broken vertical bar 2] annulation of isoindigos and Morita Baylis Hillman carbonates has been developed for the highly efficient and one-step preparation of highly steric dispiro[cyclopent3'-ene]bisoxindoles with two all-carbon quaternary spirocenters and three adjacent cycles in excellent yields (up to >99%) and diastereoselectivities (up to >20 : 1) under mild conditions within a few minutes. A series of dispiro[cyclopent-3'-ene]bisoxindoles were obtained and scale-up experiment was conducted with excellent results demonstrating the potential applications of this protocol.