To further demonstrate the application of this catalytic method, the analogous tandem cyclization of oxindoles and β-arylethenesulfonyl fluorides was next examined. Interestingly, under standard reaction conditions, δ-sultone fused indole 5a was formed in 66% yield. Switching the solvent to DMF, the yield was improved to 92%. Under this modified reaction conditions, we then investigated the substrate scope of this tandem annulation reaction. As shown in Table . Oxindole 4a reacted with different substituted β-arylethenesulfonyl fluorides to provide the corresponding δ-sultone fused indoles in high yield (5aa-5ai). N-methyl substituted oxindole 4j reacted with 2a to afford 5aj in 52% yield.