The synthesis and reactions of some fluorinated polycyclic polyenes

Abstract

Perfluorocyclohexa-l,3-diene gave the expected 1,4-adducts with cyclohexene, cyclopentene,1,2H-octafluorocyclohexene, 1H,2H-hexafluorocyclopenteneand lH,2H-tetrafIuorocyclobutene; reaction with 1H,2H-tetrafluorocyclobutene also yielded two 2,2-difluorovinyldecafluorobicyclo[4,2,0]oct-2-enes and the dimer 3,3,4,4,7,7,8,8-octafluorotricyclo[3,3,0,0(^2,4)]octane. Dehydrofluorinatlon of the adducts from 1H,2H-octafluorocyclohexene and 1H,2H-hexafluorocyclopentene gave the trienes, perfluorotricyclo[5,2,2,0(^2,7)]dodeca-2,6,9-triene and perfluorotricyclo[5,2,2,0(^2.6)]undeca-2,5,8-triene respectively. Perfluorotricyclo[5,2,2,0(^2,6)]undeca-2,5,8-triene reacted as a diene in Diels-Alder reactions with ethylene, propyne and but-2-yne. The 1,4-adducts with alkynes could be pyrolysed selectively to either polyfluorobenzobicyclo-[2,2,2]octa-2,5-dienes or 2,3-disubstituted hexafluoronaphthalenes. Irradiation of perfluorotricyclo[6,2,2,0(^2,7)]dodeca-2,6,9-triene and perfluorotricyclo[5,2,2,0 (^2,6)]undeca-2,5,8-triene in the vapour phase with UV radiation resulted in their isomerisation to perfluorotetracyclo[6,2,2,0(^2,7)0(^5,7)]-dodeca-2,9-dienes and perfluorotricyclo[5,2,2,0(^2,6)]undeca-2,3,8-triene respectively. Arguments presented support the latter isomerisation being a photochemical 1,5-sigmatropic migration of a fluorine atom. Vacuum pyrolysis of perfluorotricyclo[5,2,2,0(^2.6)]undeca-2,5,8-triene provides perfluoroindene in good yield. Irradiation of 2H-heptafluorocyclohexa-1,3-diene in the vapour phase with UV radiation yielded 2H-heptafluorobicyclo[2,2,0]hex-2-ene, the isomerisation proceeding in the reverse direction on pyrolysis; the photoisomer was of the same order of dienophilicity as perfluorobicyclo[2,2,0]-hex-2-ene towards furan. Perfluoroindene reacted readily with the nucleophiles sodium borohydride, sodium methoxide and lithium methyl replacing initially one of the vinylic fluorines in the five-membered ring. Its olefinic character was evident from the formation of a mixture of hydrazones on reaction with hydrazine hydrate and the isolation of l,l,3,4,5,6,7-heptafluoroindan-2-one from its reaction with oleum; intermediate unstable compounds formed in the latter transformation suggest that the initial stage in the reaction is the formation of the β sultone of perfluoroindene.