Abstract
Unusual alkenes, exo,exo-4,8-etheno-1,1,3,3,5,5,7,7-octafluoro-2,6-dioxaperhydro-s-indacene (1) and exo,exo-4,8-etheno-1,1,3,3-tetrafluoro-2,6-dioxaperhydroindacene (2), as well as their nonfluorinated analogue 3 were synthesized. The structures of 1 and 3 have been determined in the solid state by X-ray crystallography and of all three compounds in solution by 1H, 19F, and 13C NMR spectroscopy. The chemical properties of compounds 1−3 were investigated and compared. The double bond in fluorinated polycycloalkenes 1 and 2 was found to be totally inert toward bromination, hydrogenenation, and oxidation with m-chloroperbenzoic acid and ozone. This is in contrast to nonfluorinated indacene 3, which behaves like a normal alkene, readily adds bromine and hydrogen, and reacts with oxidants. The only successful chemical transformation of 1 was achieved by treatment with Mn2O7, which led to oxirane 15 and rearranged pentacyclic acetal 16. An interesting skeletal rearrangement occurred in the course of bromination of 3 leading to bicyclic tetrabromo derivative 12. High chemical inertness of polyfluoroindacenes 1 and 2 has been attributed mainly to through-space electronic interactions of the double bond with proximal fluorine atoms.
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