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

Abstract

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 CH(2)CH(2)CH(2)SCHCF(2)CHFCF(3) (1), CH(2)CH(2)CH(2)SCHCF(2)CHFCF(2)C(6)F(5) (2), CH(2)CH(2)CH(2)SCHCFCHFCF(2)CF(2) (3), and CH(2)CH(2)CH(2)SCHCClCHClCF(2)CF(2) (4), respectively. Pentamethylene sulfide reacts analogously with hexafluoropropene to give CH(2)CH(2)CH(2)CH(2)SCHCF(2)CHFCF(3) (8). Reaction of 1,4-thioxane with hexafluoropropene or perfluoroallylbenzene gives a mixture of two products, OCH(2)CH(2)SCH(2)CHCF(2)CHFCF(3) (9) and SCH(2)CH(2)OCH(2)CHCF(2)CHFCF(3) (10) or OCH(2)CH(2)SCH(2)CHCF(2)CHFCF(2)C(6)F(5) (11) and SCH(2)CH(2)OCH(2)CHCF(2)CHFCF(2)C(6)F(5) (12), respectively. Fluorinated alcohols C(6)F(5)CF(2)CHFCF(2)C(CH(3))(2)OH (15), C(6)F(5)CF(2)CHFCF(2)CH(CH(3))OH (16), and C(6)F(5)CF(2)CHFCF(2)CH(2)OH (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 C(6)F(5)CF(2)CHFCF(2)C(CH(3))(2)OC(6)F(5)CN (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) Å(3), D(calc) = 1.768 mg/m(3), Z = 8, and R = 0.0617. Compound 19 crystallizes in the triclinic system, space group P&onemacr;, with a = 8.103(3) Å, b = 8.790(3) Å, c = 9.832(3) Å, alpha = 66.25(4) degrees, beta = 72.01(3) degrees, gamma = 80.19(4) degrees, V = 608.7(4) Å(3), D(calc) = 1.845 mg/m(3), Z = 2, and R = 0.0346.