Polyfluorocyclopentadienes. Part VII. Synthesis of perfluoronorbornadiene and perfluoronorbornene from perfluorocyclopentadiene

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Abstract
Perfluorocyclopentadiene combines thermally with bis(trimethylstannyl)acetylene to yield a Diels–Alder adduct, 1,2,3,4,7,7-hexafluoro-5,6-bis(trirnethylstannyl)bicyclo[2,2,1]hepta-2,5-diene (1). Cleavage of the C–Sn bonds in this adduct with hydrogen chloride to give 1,2,3,4,7,7-hexafluorobicyclo[2,2,1]hepta-2,5-diene and with chlorine, bromine, or iodine to give 2,3-dihalogenohexafluorobicyclo[2,2,1]hepta-2,5-dienes proceeds smoothly to give excellent yields of the expected bicycloheptadienes, in contrast to cleavage with fluorine. The chlorinolysis product, 2,3-dichloro-1,4,5,6,7,7-hexafluorobicyclo[2,2,1]hepta-2,5-diene (2) reacts with cobalt trifluoride to give 2,3-dichloro-1,2,3,4,5,5,6,6,7,7-decafluorobicyclo[2,2,1]heptane; zinc-dechlorination of the last product provides perfluorobicyclo[2,2,1 ]hept-2-ene (perfluoronorbornene) and 2-chloro-1,3,4,5,5,6,6,7,7-nonafluorobicyclo[2,2,1]hept-2-ene. Photochemical chlorination of the dichlorohexafluorodiene (2) gives a mixture of 5,5,6,6-tetrachloro-1,2,3,4,7,7-hexafluorobicyclo[2,2,1]hept-2-ene and 2,3,5,6-tetrachloro-1,4,5,6,7,7-hexa-fluorobicyclo[2,2,1]hept-2-ene; fluorination with cobalt trifluoride of this mixture followed by zinc-dechlorination of the isomeric tetrachloro-octafluorobicyclo[2,2,1]heptanes thus obtained yields perfluorobicyclo[2,2,1]hepta-2,5-diene (perfluoronorbornadiene) and 2-chloro-1,3,4,5,6,7,7-heptafluorobicyclo[2,2,1]hepta-2,5-diene.

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