Novel generation of arylsulfenium ion intermediates and efficient aromatic arylthiolation by the intermediates

Abstract

Reactions of hydrazoic acid and alkyl azides with alkyl aryl sulfide in trifluoroacetic acid containing trifluoromethanesulfonic acid or H₂SO₄ proceeded through an S-arylaminosulfonium ion and a protonated S-arylsulfenamide, giving efficiently S-alkylthiophenyl aryl sulfide via an arylsulfenium ion interacting with both the counter-anion and the unshared electron pair of the amine. The use of the S-arylsulfenamide instead of the azides also afforded the above product by aromatic arylthiolation in a good yield via the sulfenium ion along with its ortho-isomer, diaryl disulfide and diaryl sulfide. The formation of the sulfenium ion was demonstrated by the effect of the counter-anion, the-amine, the aryl substituent of the sulfenamide and the solvent nucleophilicity. We ruled out the possibility that the arylthiolation occurs via an arylthiyl radical and an aminium radical from the sulfenamide and by direct reaction of the protonated sulfenamide with alkyl aryl sulfides.