Hydrogenolysis reactions of some polychlorinated norborn-2-enes, and the synthesis of 1,4-dichloronorborn-2-ene

Abstract

Hydrogenolysis of 1,2,3,4,7,7-hexachloronorborn-2-ene over Raney nickel in the presence of potassium hydroxide affords 1,4,7-trichloronorbornane by way of the intermediate 1,2,3,4,7-syn-pentachloronorborn-2-ene. When 10% palladium–charcoal is used as catalyst the C-7 chlorine atoms are inert unless a 5-endo-chloro-substituent is present, as in 1,2,3,4,5-endo,7,7-heptachloronorborn-2-ene. Hydrogenolysis of the Diels–Alder adducts from the reactions of tetrachlorocyclopentadiene with trans-1,2-dichloroethylene and vinyl chloride results in removal of their chlorine-substituted double bonds. 1,4-Dichloronorborn-2-ene was synthesised by the elimination of chlorine from 1,2-exo,3-endo,4-tetrachloronorbornane when treated with magnesium and iodine, and by base-catalysed elimination of hydrogen chloride from 1,2-exo,4-trichloronorbornane.