Light-initiated Perfluoroalkylation Reactions of Alkenes in water

MARIEL SLODOWICZ; ALBERTO POSTIGO

MENDOZA

Conferencia; 21ST I-APS Conference (Interamerican Photochemical Society); 2011

IAPS-INTERAMERICAN PHOTOCHEMICAL SOCIETY

Perfluoroalkyl-substituted compounds are regarded as important components of fluorophors and for the introduction of fluorous tags into organic substrates. Their syntheses in organic solvents are achieved through different methods, among which, the addition of perfluoroalkyl radicals to unsaturated bonds represents a convenient choice. On the other hand, intermolecular radical reactions in water have attracted the attention of synthetic chemists as a strategic route to carbon-carbon bond formation reactions. In previous works[1] we have reported the radical perfluoroalkylation reaction of alkenes mediated by silyl radicals, and obtained perfluoroalkyl-substituted compounds in fairly good yields. The radical triggering events employed consist of the thermal decomposition of an azo compound and the dioxygen initiation. Our results indicate that for intermolecular carbon-carbon bond formation reactions mediated by (Me3Si)3SiH, the decomposition of the azo compound 1,10- azobis(cyclohexanecarbonitrile) (ACCN) is the best radical initiator. In this work we undertook the intermolecular addition of perfluoroalkyl radicals on electron rich alkenes and alkenes with electron withdrawing groups in water, initiated photochemically. The lack of hydrogen donor (i.e.: (Me3Si)3SiH) in our reaction medium facilitates a Halogen Atom Transfer reaction (HAT), affording the respective perfluoroalkylated alkyl halide in good yields. We also found that water exerts a relevant solvent effect on the rates of perfluoroalkyl radical additions onto double bonds. Our account provides a versatile and convenient method to achieve perfluoroalkylation reactions of alkenes in water to render perfluoroalkylated haloalkanes as key intermediates in the synthesis of fluorophors and other fluorinated materials. This is the first report where perfluoroalkyl-substituted alkanes are synthesized through intermolecular radical carbon-carbon bond formation reactions in water, induced by light. [1] Barata-Vallejo, Sebastián; Postigo, Al. “(Me3Si)3SiH-Mediated Intermolecular Radical Perfluoroalkylation Reactions of Olefins in Water”. J.Org.Chem. 2010, 75, 6141-6148.