Synthesis and derivatives of para-bonded isomers of fluoroaromatic compounds
Abstract
Some fluoroamatic compounds have been photoisomerised to bicyclo[2,2,0]hexa-2,5-diene derivatives, which were re-aromatised on heating. Hexafluorobenzene gave hexafluorobicyclo[2,2,0]hexa-2,5-diene in good yield. This compound added bromine and hydrogen, and gave 2,5- and 2,6-disubstituted products on treatment with sodium ethoxide or methyl-lithium; phenylation afforded 1-fluoropentaphenyl- and 1,4-difluorotetraphenylbenzene; on treatment with aluminium chloride in methylene chloride and with aluminium iodide in methyl iodide, 1-chloropentafluoro-, 1,4-dichlorotetrafluoro-, and 1-iodopentafluoro-bicyclo[2,2,0]hexa-2,5-diene, respectively, were obtained. 2H-Pentafluorobicyclo[2,2,0]hexa-2,5-diene was obtained from pentafluorobenzene in low yield, and was also synthesised by a different route. Octafluorotoluene gave perfluoro-1- and -2-methylbicyclo-[2,2,0]hexa-2,5-diene. The former added bromine and hydrogen; the latter added bromine and hydrogen fluoride and could be dimerised. Decafluoro-p-xylene gave perfluoro-1,4- and -2,5-dimethylbicyclo[2,2,0]hexa-2,5-diene in low yield.