[3 + 3] Formal Cycloadditions of Nitrones from Isatins and Azaoxyallyl Cations for Construction of Spirooxindoles

A [3 + 3] formal cycloaddition reaction between in situ formed azaoxyallyl cations and nitrones from isatins has been developed, furnishing a spectrum of spiro[1,2,4‐oxadiazinan‐5‐one]oxindoles in good to excellent yields with excellent diastereoselectivity. This method provides direct and efficient access to potentially bioactive spirooxindoles incorporating a six‐membered heterocyclic scaffold.