Some studies of polyfluorinated polycyclic polyenes

Abstract

The attempted addition of difluorocarbene, which was generated from hexafluoropropene epoxide, to polyfluorinated cyclic olefins was largely unsuccessful, although perfluorobicyclo[4,l,0]hept-3-ene was isolated from the addition to perfluorocyclohexa-1,4-diene. It seems that difluorocarbene adds to the polyfluorinated cyclic olefins to form cyclopropanes, which readily eliminate difluorocarbene under the reaction conditions required for their formation. The attempted photochemical isomerisations of pplyfluorobicyclo[2,2,2]octa-2,5-dienes, via the [2π+2π] ring closures to their corresponding tetracycles, were also unsuccessful. However, on irradiation dimethyl 1,4,5,6,7,7,8,8- octafluorobicycloC2,2,2]octa-2,5-diene-2,3-dicarboxylate formed a tricyclic biradical, which abstracted a hydrogen from the a methylene group of the diethyl ether solvent to give isomers of dimethyl 2-(3'-oxa-2'-pentyl)-l,4,5,6,7,7,8,8- octafluorotricycloC2,2,2,0(^3,5)]octane-2,3-dicarboxylate. The tricyclic biradical intermediate is similar to that proposed for the photochemical isomerisation of hydrocarbon bicyclo[2,2,2]hepta-2,5-dienes and their analogues. In contrast to their corresponding hydrocarbon analogues the tricyclic biradical intermediates formed on irradiation of polyfluorobicyclo[2,2,2]octa-2,5-dienes donot appear to form tetracycles. Perfluorotricyclo[6,2,2,0(^2,7)]dodeca-2,6,9-triene reacted as a diene in the Diels-Alder reactions with ethylene, but-2-yne, acetylene dicarboxylic acid dimethyl ester, perfluoroacetonitrile, tetrafluoroethylene and lH,2H-hexafluoro- cyclopentene. As a consequence imposed by the carbocyclic framework of the diene, the addition of lH,2H-hexafluorocyclopentene gave the exo adduct. The 1,4- alkyne adducts were pyrolysed to give 2,3-disubstituted hexafluoronaphthalenes. The pyrolysis of perfluorotricycloC6,2,2,0(^2,7)]dodeca-2,6,9-triene proceeds nvia a 1,3-alkyl migration to give perfluorotricyclo[8,2,0,0(^2,7)] dodeca-2,6,8-triene which subsequently eliminates tetrafluoroethylene to give perfluoro-l,2-dihydro- 2,7naphthalene as the major product. The reaction of perfluorotricyclo[6,2,2,0(^2,7)]-dodeca-2,6,9-triene with lithium methyl in ether proceeded preferentially at the diene moiety. The pyrolysis of the monomethyltridecafluorotricyclo[6,2,2,0(^2,7)]- dodeca-2,6,9-trienes gave monomethylnonafluoro-1,2-dihydronaphthalenes which had the methyl label in the non-aromatic ring. Nucleophilic substitution in perfluoro-1,2-dihydronaphthalene was found to occur only at the vinylic C] position with sodium borohydride whereas with lithium methyl four monomethyl substitution products were obtained, both the vinylic, the C6 and C7 fluorines being replaced. The gas phase photochemical reaction of perfluoro-1,2-dihydronaphthalene produces the perfluoro-1- and -2- methylenindanes possibly via the perfluorovinyl-o-quinodimethane.