Organocatalytic synthesis of δ-sultone-fused benzofurans by the tandem reaction of β-arylethenesulfonyl fluorides

An organocatalytic annulative sulfur(VI)-fluoride exchange (SuFEx) reaction of β-arylethenesulfonyl fluorides has been reported. Under the catalysis of 10 mmol% BTMG and molecular sieves 4Å, β-arylethenesulfonyl fluorides undergo Michael addition-intramolecular SuFEx click reaction with benzofuran-3(2H)-ones to give δ-sultone-fused benzofurans in 76-99% yield. Using 10 mmol% DBU and molecular sieves 4Å, β-arylethenesulfonyl fluorides coupled with oxindoles to produce δ-sultone-fused indoles in 81-85% yield. In these reactions, molecular sieves 4Å act as efficient HF scavenger, which avoid the using of stoichiometric silicon additives and bases. Importantly, density functional theory (DFT) calculations reveal that Michael addition is a decisive speed step for the reaction.