Abstract Approaches to Si-disubstituted 1-thia-5-silacyclooctanes based on homolytic addition of hydrogen sulfide to diallylsilanes R 2 Si (CH 2 CH= CH 2) 2 and on intramolecular cyclization of Si-disubstituted (allyl)(γ-sulfanylpropyl) silanes have been studied. In the former case the reactivity of the silanes decreases in the order R= MeO> F> Me> Ph, whereas in the latter case the reactivity order is slightly different: Me> MeO≈ F≫ ...