Valence-bond isomer chemistry. Part 13. Photochemical oxidation of hexafluorobenzene: formation of hexafluoro-3-oxatricyclo2,4>hept-6-ene and its reactions

Article abstract of DOI:10.1016/S0022-1139(00)80429-7

Vapour-phase ultraviolet irradiation of hexafluorobenzene in the presence of oxygen slowly yields hexafluoro-3-oxatricyclo<3.2.0.0^2,4>hept-6-ene (2) (10percent).The CF=CF bond in 2 adds (yields of adducts given) the dienes; cyclopentadiene (74percent), furan (61percent) and 2,5-diphenylisobenzofuran (59percent); benzonitrile oxide (58percent); chlorine (59percent) and bromine (71percent) photochemically.Heptene 2 isomerises thermally hexafluorocyclohexa-2,4-dienone (6) (60percent) at 50 deg C, and reacts with diethyl ether at room temperature yielding ethyl fluoride (89percent) and 2-ethoxypentafluorocyclohexa-2,5-dienone (21percent).The benzonitrile oxide adduct, upon flow pyrolysis at 440 deg C, yields an isomeric oxepin derivative and the cyclohexadienone 6 with longer contact times.The chlorine adduct similarly yields a dichloro-oxepin derivative; attempts to dechlorinate this to hexafluoro-oxepin were unsuccessful.Benzonitrile oxide adds to one or both of the C=C bonds of hexafluorobicyclo<2.2.0>hexa-2,5-diene; the 1:1 adduct isomerises thermally to the benzonitrile oxide-hexafluorobenzene adduct.