Lewis Base-Mediated [3 + 3] Cycloaddition of <i>N</i> -2,2,2-Trifluoroethylisatin Ketimines with Diazo Esters: Synthesis of Trifluoromethyl-1,2,4-triazine-spirooxindoles

A facile and efficient DBU-mediated [3 + 3] cycloaddition reaction of <i>N</i>-2,2,2-trifluoroethylisatin ketimines with diazo esters for the synthesis of trifluoromethyl dihydro-1,2,4-triazine-spirooxindole derivatives has been developed. The reaction proceeds under mild conditions with a broad substrate scope, tolerating various electronically and sterically diverse substituents to afford moderate to excellent yields. Furthermore, a one-pot cycloaddition/oxidation strategy is established to achieve efficient synthesis of trifluoromethyl-1,2,4-triazine-spirooxindoles. This study not only enriches the structural diversity of spirooxindoles but also provides a valuable synthetic tool for developing novel bioactive molecules in medicinal chemistry.