The First Bidirectional [4+2] Cycloadditions of Benzo[1,2:4,5]dicyclobutenes: Synthesis of Benzo[1,2-f:4,5-f′]diisoindole-1,3,7,9-tetraones

Bidirectional reactions are an efficient tool for the synthesis of larger, often symmetric compounds. Whereas the ring opening of benzocyclobutene derivatives with subsequent cycloaddition of the ortho-quinodimethanes formed has been used extensively for the syntheses of various classes of compounds such as steroids, acenes, and natural as well as synthetic oligocycles including heterocyclic systems, the respective bidirectional reactions have barely been explored. Here, the first bidirectional cycloadditions starting from benzo[1,2:4,5]dicyclobutene derivatives are presented using N-methylmaleinimide as the dienophile. The benzo[1,2:4,5]dicyclobutene derivatives used have in common that they are dimethylacetals of the respective diones. As a consequence, the cycloadducts easily undergo elimination of methanol. Subsequent dehydrogenations generate the aromatic anthracene systems, which are part of the benzo[1,2-f:4,5-f]diisoindole-1,3,7,9-tetraone derivatives formed as the final products.