Abstract: The reaction of a variety of saturated heterocyclic compounds with 5-membered ring containning tricoordinated phosphorus with trifluoroethyl benzenesulfenate or hexafluoroisopropyl benzenesulfenate yielded a series of corresponding cyclic phosphoranes. Variable temperature ¹⁹FNMR studies of these compounds showed no change down to - 60℃ Reaction of compound(7) with excess trifluoroethyl benzenesul fenate yielded pentakis(trifluoethoxy) phosphorane (19), diphenyl disulfite(20) and compound(21)Compound(11) reacted with hexafluoroisopropyl benzenesulfenate to give compound (18) and (21). The mechanism of these reactions are discussed.