Cope rearrangements of diels-alder adducts containing norbornene and norbornenone systems

The product formed from cyclopentadiene and the cyclo-octatetraene dimer 5a has been shown to possess structure 6a, probably resulting from Cope rearrangement of an initial adduct 4a. The reaction of tetraphenylcyclopentadienone with 1 - methoxybuta - 1,3 - diene yields a mixture of the exo-adduct 14 and the rearranged endo-adduct 13 Rearrangement of the norbornenone derivative 27 gives the Cope product 29 Treatment of the 4,5-fused 2,3,4,5-tetrachlorocyclopent-2-enones 29,40 and 41 with powdered sodium hydroxide in tetrahydrofuran results in ring-cleaveage with the formation of 2,3,5-trichlorobuta-2,4-dienoic acid derivatives, 36, 43 and 44 respectively.