Selenium-promoted cyclization of unsaturated thioacetate 5 provides the selenyltetrahydrothiophene 12 or the sulfanyl acetate 13, depending on the selenium reagent used. On the other hand, electrophile-induced cyclization of 1-sulfanyl-4-penten-2-ol derivatives 23−25 depends on the electrophile used. Iodothioetherification of benzyl sulfide 25 followed by oxidation affords unsaturatedsulfone 26 as a result of 6-endo-cyclization