The Flash Vacuum Thermolysis (FVT) of dispiro [2.2. 6.2]-tetradeca-4, 13-diene (7a), dispiro [2.2. 5.2] trideca-4, 12-diene (7b) and dispiro [2.2. 2.2] deca-4, 9-diene (7e) at 500–750° C is reported. The complicated reaction mixture from 7a and 7b (Scheme 3) included at lower temperatures vinylspiroalkadienes 9, ethylidenespiroalkadiene 10b, β- ethylcycloalkabenzenes 11, while at higher temperatures, pn-alkyl-(5) and p-sec- ...