INTRAMOLECULAR CYCLIZATION TO 1-PHENYL-1-BENZOTHIOPHENIUM SALTS BY ELECTROPHITIC ADDITION OF O-(PHENYLSULFANYL) PHENYLALKYNES

Electrophilic addition of -(phenylsulfanyl)phenyl]-2-(p-methoxyphenyl) ethyne with electrophiles such as perchloric acid. tetrafluoroboric ac id, bromine, and benzenesulfenyl chloride gave 1-phenyl-1-benzothiophe nium salts exclusively. The substituent effect on the intramolecular c yclization with electrophiles has been examined. The aryl-substituted alkynes afforded predominantly the cyclized 1-phenyl-1-benzothiopheniu m salts but methyl-substituted alkynes yielded a mixture of the cycliz ed salt and the 1,2-addition product. In addition to the intramolecula r cyclization at the intermediate vinyl cation or bridged ion, it is p roposed, on the basis of the product from the reaction of methyl-subst ituted alkyne, that the pi complex partly participates in the intramol ecular cyclization.