Efficient Access to Extended Yagupolskii–Umemoto‐Type Reagents: Triflic Acid Catalyzed Intramolecular Cyclization of <i>ortho</i>‐Ethynylaryltrifluoromethylsulfanes

Abstract

King of the ring: S-(trifluoromethyl)benzo[b]thiophenium salts 1, as analogues of Yagupolskii–Umemoto type reagents, were synthesized by novel triflic acid catalyzed intramolecular cyclization of ortho-ethynylaryltrifluoromethylsulfanes 2. 1 j is especially useful for the electrophilic trifluoromethylation of β-ketoesters and dicyanoalkylidenes.