Reactions of chlorocyclopentadienes with prop-2-ynyl bromide and bromoallene

Abstract

The reaction between hexachlorocyclopentadiene and prop-2-ynyl bromide affords the Diels–Alder adduct 1,2,3,4,7,7-hexachloronorborna-2,5-dien-5-ylmethyl bromide, its allylic rearrangement product 6-endo-bromo-1,2,3,4,7,7-hexachloro-5-methylenenorborn-2-ene, and 5-bromomethylene-1,2,3,4,7,7-hexachloronorborn-2-ene. The last compound has its origin in the Diels–Alder addition of hexachlorocyclopentadiene to bromoallene, which is produced in the thermal isomerisation of prop-2-ynyl bromide under the reaction conditions. The reactions of 1,2,3,4-tetrachlorocyclopentadiene and of 1,2,3,4,5-pentachlorocyclopentadiene with prop-2-ynyl bromide lead to comparable products. The Diels–Alder addition of the chlorocyclopentadienes to pure bromoallene affords only the 5-bromomethylene compounds, apart from a trace of 6-endo-bromo-1,2,3,4,7,7-hexachloro-5-methyl-enenorborn-2-ene as an additional minor product from hexachlorocyclopentadiene and bromoallene.