Organocatalytic Synthesis of δ‐Sultone‐Fused Benzofurans and Indoles by Annulative SuFEx Reactions 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 mol% BTMG and molecular sieves 4 Å, β‐arylethenesulfonyl fluorides undergo Michael addition‐intramolecular SuFEx click reaction with benzofuran‐3(2 H )‐ones to give δ‐sultone‐fused benzofurans in 72%–99% yields. Under similar reaction conditions, β‐arylethenesulfonyl fluorides couple with oxindoles to produce δ‐sultone‐fused indoles in 62%–92% yields. In these reactions, molecular sieves 4 Å act as efficient HF scavenger, which avoid the using of stoichiometric silicon additives and bases. Density functional theory (DFT) calculations reveal that the Michael addition is the rate‐determining step for the reaction.