[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.