Insertion of Fluoroalkenes into Activated CH Bonds for the Preparation of Polyfluorinated Sulfanes, Alcohols, and Acyclic and Cyclic Ethers

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 CH₂CH₂CH₂SCHCF₂CHFCF₃ (1), CH₂CH₂CH₂SCHCF₂CHFCF₂C₆F₅ (2), CH₂CH₂CH₂SCHCFCHFCF₂CF₂ (3), and CH₂CH₂CH₂SCHCClCHClCF₂CF₂ (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 SCH₂CH₂OCH₂CHCF₂CHFCF₃ (10) or OCH₂CH₂SCH₂CHCF₂CHFCF₂C₆F₅ (11) and SCH₂CH₂OCH₂CHCF₂CHFCF₂C₆F₅ (12), respectively. Fluorinated alcohols C₆F₅CF₂CHFCF₂C(CH₃)₂OH (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)₂OC₆F₅CN (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) Å, b = 18.471(0) Å, c = 11.702(0) Å, V = 3992.5(9) ų, D_calc = 1.768 mg/m³, Z = 8, and R = 0.0617. Compound 19 crystallizes in the triclinic system, space group P1̄, with a = 8.103(3) Å, b = 8.790(3) Å, c = 9.832(3) Å, α = 66.25(4)°, β = 72.01(3)°, γ = 80.19(4)°, V = 608.7(4) ų, D_calc = 1.845 mg/m³, Z = 2, and R = 0.0346.