HIGHLY CONDENSED POLYCYCLIC SYSTEMS .2. PENTACYCLO[7,2,1,0,0,0]DODEC-4-ENES

Hexachlorocyclopentadiene and tetrachlorocyclopentadienone acetals undergo thermal (4 + 2)π cycloadditions with cyclohepta-1,3,5-triene. The resulting endo-1:1-adducts contain a 1,3-diene system and an isolated double-bond; prolonged heating of these adducts effects intramolecular Diels-Alder addition of these structural features with the formation of pentcyclo[7,2,1,0 2,8,03,11,6,10]dodec-4-enes. Bromination of the hexachlorocyclopentadiene-cycloheptatriene adduct involves selective attack on the 5,6-double bond and yields a cis-diequatorial dibromide.