Reaction of [o-(arylthio)phenyl] ethenes with bromine or IC1 undergoes intramolecular cyclization to give 1-aryl-1-benzothiophenium salts. Electrophilic addition of [o-(phenylthio)phenyl] alkynes with electrophiles such as HClO4, HBF4, Br2, and PhSCl also affords 1-phenyl-1-benzothiophenium salts. Copper-catalyzed reaction of 1-benzothiophenes with diphenyliodonium triflate gives 1-phenyl-1-benzothiophenium triflates directly. This method is especially effective for the synthesis of parent

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... nyl-1-benzothiophenium salt. Reaction of 1-phenyl-1-benzothiophenium salts with halide ions leads to the formation of 1-benzothiophenes and (Z)-haloethenes . while the reaction with alkoxide ions provides only (Z)-alkoxyethenes. In the cases of 2-alkyl-subsituted and 3-unsubstituted benzothiophenium salts, allenes and alkynes are formed, respectively . Cycloaddition of 1-phenyl-1-benzothiophenium salts with cyclopentadiene or 1, 3-diphenylisobenzofuran proceeds efficiently in the cases of less substituted 1-phenyl-1-benzothiophenium salts . Phenyl migration is observed in the thermolysis of 1-phenyl-1-benzothiiophenium triflates , while the phenyl migration competes with the dephenylation in the photolysis . The reactions observed in this study are attributed to the loss of aromaticity of the thiophene ring .