Dibenzotricycloöctadiene (I) yields on heating with dienophiles, Diels-Alderadducts (IV and V) and forms with oxygen a peroxide (VI). These reactions are explained by formation of an intermediate with an ortho-quinonoid structure (II). Polycyclic Diels-Alderadducts were obtained in good yields from a solution of benzocyclobutadiene and unstable hydrocarbons such as ortho-quinodimethane or 2,3-dihydronaphthalene