REACTIONS OF CYCLO-OCTATETRAENE AND ITS DERIVATIVES-IX. CYCLOPENTADIENONE ADDUCTS OF TRICYCLO2,5>DECA-3,7-DIENES AND TRICYCLO2,5>NONA-3,7-DIENES

Article abstract of DOI:10.1016/0040-4020(80)88029-X

Tetracyclo<8.2.2.0^2,9.0^3,8>tetradeca-4,6,11-trienes 5 are produced from tricyclo<4,2,2,0^2,5>deca-3,7-dienes 1 by reaction with cyclopentadienones 2 (or equiv) followed by thermal decarbonylation.With tetraphenylcyclopentadienone, however, the product 5e rearranges under the conditions required for its formation to give the dihydrosemibullvalene 11.The rearrangement evidently proceeds via the cyclo-octa-1,3,5-triene 14, the ring-opening 5e-14 being facilitated by a phenyl-conjugation effect, uncovered in another series of experiments involving the reaction of cyclopentadienone s with the tricyclo<4.2.1.0^2,5>nona-3,7-diene 16.Thus the tetraphenylcyclohexa-1,3-diene 18c undergoes ring-opening in refluxing xylene to afford the cyclo-octa-1,3,5-triene 21a, whereas the dimethyldiphenyl-analogue 18b resists valence isomerisation under these conditions.