4 5 of the Diels-Alder adducts of the bicyclic tautomer 3 with tetracyanoethylene or 6. Elimination of HBr to give 5 was effected by potassium t-butoxide in dichloromethane. To establish the position of the two bromine atoms, 5 was converted to 1, 4- dimethylcyclooctatetraene (4, 95%, bp 60-62"(12mm); n 2 5~, 1.5206"; nmr (CDC1,) 2CH3, s, r 8.30) by lithium dimethylcopper. 2 Catalytic hydrogenation of 4 gave 1, 4- ...
