Initially, the reaction of phenyl allyl ketone 1a and β-phenyl-substituted ethenesulfonyl fluoride 2a was examined. In the presence of 20 mol% DBU, γ-ethenylated δ-sultone 3a was obtained in 48% yield in DMSO at room temperature (Table , entry 1). We concluded HF generated in the reaction neutralized DBU and thus quenched the reaction. Increasing the amount of DBU to 1.0 equivalent, the yield of 3a was improved to 60% ). However, triethylamine and DIPEA promoted the reaction in low efficiently (Table and). Pleasingly, Inorganic bases such as Na 2 CO 3 , K 2 CO 3 , Cs 2 CO 3 and NaHCO 3 mediated the reaction in high yields (Table ). Further study showed that the combination of catalytic amount of DBU and stoichiometric amount of inorganic base can promote the reaction to afford the desired product in excellent yield (Table and). Interestingly, when 4 Å Molecular sieves was used instead of inorganic bases, DBU can also catalyze the tandem reaction in 96% yield (Table , entries 11-13). A brief screening of the reaction solvent showed that high polar solvents such as DMSO, DMF and acetonitrile give the desired product in high yield (Table , entries 12, 14 and 15), while DCM, THF, ethyl acetate showed low efficiency (Table , entries 16-18). Finally, control experiment showed that in the absence of DBU, no desired product was formed (Table , entry 19). Having evaluated the optimal reaction conditions, we then investigated the substrate scope of this tandem annulation reaction. As shown in Table , both electron-withdrawing and electron-donating substituents substituted aryl allyl ketones participated in the reaction efficiently, producing the corresponding δ-sultones in high yields (3a-3f). However, very strong electron-withdrawing cyanide group substituted allyl ketone only gave the desired product in moderate yield (3g). Different positions of the substituents have no obvious effect on the reaction yield (3h-3k).