New unsaturated sulfur-containing heterocycles derived from 1,3-dithiane or 1,3,5-trithiane and α -ferrocenylvinyl cation generated from ethynylferrocene

• Protonation of ethynylferrocene with Nafion film in sc-CO 2 . • “Green” and mild preparation of ferrocenylvinyl sulfonium salts. • 1,3-Dithiane and 1,3,5-trithiane based vinyl sulfoniums. • Rearrangements of vinyl sulfoniums to thiacyclooctenes . Ferrocenylacetylene 1 protonates a superacidic polymer Nafion in sc-CO 2 (35 °C, 9 MPa) to form the α -ferrocenylvinyl cation, FcC + =CH 2 ( 2 , Fc = ferrocenyl). Carbocation 2 alkenylates in situ 1,3-dithiane or 1,3,5-trithiane (35 °C, 35 MPa) to give the mono and disulfonium salts with Nafion anion. An anion exchange in the last ones for tetrafluoroborate afforded the disulfonium salts 4 and 12 , whose deprotonation produced, after a sequence of transformations, the neutral unsaturated 8-membered heterocycles, 2-ferrocenyl-3,7-dithiacyclooct-1-ene 10 and 2-ferrocenyl-3,5,7-tritiacyclooct-1-ene 14 . Along with 14 , the reaction of 1 with 1,3,5-trithiane furnished two other neutral sulfur heterocycles, 2,4-diferrocenyl-5-thiacyclohexa-1,3-diene 18 , and 1-ferrocenyl-3,5-dithiacyclohex-1-ene 23 . These transformations proceed at room temperature via the C-S bond scission followed by a formation of new C C bond. Compounds 10, 14, 18, 23 were fully characterized by the NMR spectra. The molecular structures of 10, 14, 18, 23 were elucidated by X-ray study.