XO-4,8-ETHENOPOLYFLUORO-2,6-DIOXAPERHYDROINDACENES - UNUSUAL ALKENES FLANKED WITH FLUORINE-ATOMS

Unusual alkenes, ,3,5,5,7,7-octafluoro-2,6-dioxaperhydro-s-indacene (1 ) and heno-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 crystallogra phy and of all three compounds in solution by H-1, F-19, and C-13 NMR spectroscopy. The chemical. properties of compounds 1-3 were investiga ted and compared, The double bond in fluorinated polycycloalkenes 1 an d 2 was found to be totally inert toward bromination, hydrogenenation, and oxidation with m-chloroperbenzoic acid and ozone. This is in cont rast 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 I was achieved by treatment wit h Mn2O7, which led to oxirane 15 and rearranged pentacyclic acetal 16. An interesting skeletal rearrangement occurred in the course of bromi nation of 3 leading to bicyclic tetrabromo derivative 12. High chemica l inertness of polyfluoroindacenes 1 and 2 has been attributed mainly to through-space electronic interactions of the double bond with proxi mal fluorine atoms.