Organic superbase BTMG catalyzed the annulative sulfur(VI)-fluoride exchange (SuFEx) reactions of β-arylethenesulfonyl fluorides with benzofuran-3(2H)-ones and oxindoles to afford δ-sultone-fused benzofurans and δ-sultone-fused indoles in good to excellent yields.

Abstract

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(2H)-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.