Cycloaddition of isatin-derived MBH carbonates and 3-methyleneoxindoles to construct diastereoselective cyclopentenyl bis-spirooxindoles and cyclopropyl spirooxindoles: Catalyst controlled [3 + 2] and [2 + 1] annulations

Abstract A highly diastereoselective organocatalytic synthesis of cyclopentenyl bis-spirooxindoles and cyclopropyl spirooxindoles has been achieved via [3 + 2] and [2 + 1] annulations. The tertiary amine catalysts have been effectively employed to tune the cycloaddition of isatin-derived MBH carbonates and 3-methyleneoxindoles for the outcome of two different spirooxindole frameworks with vicinal quaternary spiro centers and three contiguous stereocenters. The reactions worked under mild and practical conditions to afford the spirooxindoles in good to excellent yields with very high diastereoselectvity.