REACTIONS OF CYCLO-OCTATETRAENE AND ITS DERIVATIVES .I. CYCLOOCTATETRAENE AS A DIENOPHILE

Cyclo-octatetraene behaves as a dienophile towards tetrachlorocyclopentadienone acetals to form 1:2-adducts having the hexacyclo[12,2,1,15,8,02,13,03,10,0 4,9]octadeca-6,11,15-triene skeleton (V), probably via its valence tautomer, bicyclo[4,2,0]octa-2,4,7-triene, and intermediate 1:1-adducts thereof having the tetracyclo-[8,2,1,02,9,03,8]trideca-4,6,11- triene structure (VII). The 1:1-adduct (IIIa) of 1,2,3,4-tetrachloro-5,5- dimethoxycyclopentadiene and the dibromo-derivative of cyclo-octatetraene, when treated with concentrated sulphuric acid, yields the corresponding carbonyl-bridged compound (IIId) which then undergoes skeletal rearrangement to the αβ-unsaturated ketone (VIIIa); the transformation may be reversed by u.v. irradiation. Similarly, acid hydrolysis of the 2:1-adduct (Va) from the same tetrachlorocyclopentadienone acetal and cyclo-octatetraene is accompanied by rearrangement to the hexacyclo[8,5,2,14,7,02,9,0 3,8,011,15]octadeca-5,12,16-triene system (XVI).