Laticyclic Conjugated Polyenes. Study on Diels-Alder Cycloadditions of a Facially Dissymmetric Maleic Anhydride.

The tetracyclic ring-fused, facially dissymmetric maleic anhydride 2 was synthesized from compound 9 obtained from the Diels-Alder cycloaddition of the bicyclic ring-fused cyclohexadiene 1 and acetylenedicarboxylate. Maleic anhydride 2 readily underwent the Diels-Alder cycloadditions with anthracene, 1,3-diphenylisobenzofuran, cyclopentadiene, 1,3-cyclohexadiene, 6,6-dimethylfulvene, and o-quinodimethane. All the cycloadditions occurred exclusively on the pi-face syn to the etheno bridge of 2, thereby in cases of the cycloadditions with anthracene, cyclopentadiene, 1,3-cyclohexadiene, and 6,6-dimethylfulvene producing the corresponding adducts 11a, 18b, 22b, and 23b that contain three double bonds aligned in parallel. The structures of 18b and 22b were unequivocally established by the X-ray structural determinations. The molecular structure of maleic anhydride 2 was analyzed by X-ray crystallography to have a pyramidalized dienophilic double bond, which appeared to correlate well with the observed pi-facial selectivity.