A novel recyclable sulfur monoxide transfer reagent.

[reaction: see text]. Trisulfide 2-oxide 11 has been prepared from disulfide 9 via reduction to the corresponding dithiol and subsequent trapping with thionyl chloride. Heating trisulfide oxide 11 in the presence of dienes results in transfer of sulfur monoxide to form cyclic unsaturated sulfoxides 13 in good to excellent yields, along with recovery of disulfide 9. A Pummerer reaction can be used to convert the cyclic sulfoxides into thiophenes.