Free radical addition reactions of tetrahydrothiophene. pentamethylene sulfide, and 1,4-thioxane with various cyclic and acyclic per- and polyfluorinated olefins are readily initiated by di-tert-butyl peroxide, providing a convenient route for synthesizing cyclic sulfanes with fluorinated side groups. Tetrahydrothiophene reacts with hexafluoropropene, perfluoroallylbenzene, perfluorocyclobutene, and 1,2-dichlorotetrafluorocyclobutene in the presence of catalytic amounts of the peroxide to give the corresponding addition products CH2CH2CH2SCHCF2-CHFC3 (1), CH2CH2CH2SCHCF2CHFCF2C6F5 (2), CH2CH2CH2SCHCFCHFCF2CF2 (3), and CH2CH2-CH2SCHCClCHClCF2CF2 (4), respectively. Pentamethylene sulfide reacts analogously with hexafluoropropene to give CH2CH2CH2CH2SCHCF2CHFCF3 (8). Reaction of 1,4-thioxane with hexafluoropropene or perfluoroallylbenzene gives a mixture of two products, OCH2CH2SCH2CHCF2CHFCF3 (9) and SCH2CH2OCH2CHCF2-CHFCF3 (10) or OCH2CH2SCH2CHCF2CHFCF2C6F5 (11) and SCH2CH2OCH2CHCF2CHFCF2C6F5 (12), respectively. Fluorinated alcohols C6F5CF2CHFCF2C(CH3)(2)OH (15), C6F5CF2CHFCF2CH(CH3)OH (16), and C6F5CF2CHFCF2CH2OH (17) are prepared by reacting perfluoroallylbenzene with the corresponding alcohols. When 15 is reacted with pentafluorobenzonitrile in the presence of potassium carbonate, an unexpected cyclic ether 19 is obtained as the major product in addition to C6F5CF2CHFCF2C(CH3)(2)OC6F5CN (18). Alcohols 15-17 can be cyclized by heating with potassium carbonate to give fluorinated cyclic ethers 19-21. The X-ray crystal structures of acyclic ether 18 and cyclic ether 19 are given. Compound 18 crystallizes in the tetragonal system, space group P4(2)/n, with a = 18.471(0) Angstrom, b = 18.471(0) Angstrom, 11.702(0) Angstrom, V = 3992.5(9) Angstrom(3), D-calc = 1.768 mg/m(3), Z = 8, and R = 0.0617. Compound 19 crystallizes in the triclinic system, space group P (1) over bar, with a = 8.103(3) Angstrom, b = 8.790(3) Angstrom, c = 9.832(3) Angstrom, alpha = 66.25(4)degrees, beta = 72.01(3)degrees, gamma = 80.19(4)degrees, V = 608.7(4) Angstrom(3), D-calc = 1.845 mg/m(3), Z = 2, and R = 0.0346.