Reactions of cyclo-octatetraene and its derivatives. Part I. Cyclo-octatetraene as a dienophile

Abstract

Cyclo-octatetraene behaves as a dienophile towards tetrachlorocyclopentadienone acetals to form 1 : 2-adducts having the hexacyclo[12,2,1,1^5,8,0^2,13,0^3,10,0^4,9]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-[8,2,1,0^2,9,0^3,8]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[8,5,2,1^4,7,0^3,8,0^11,15]octadeca-5,12,16-triene system (XVI).