Abstract
Photocycloaddition reaction of 4-ethoxycarbonyl-5-phenyl-1H-pyrrole-2, 3-dione (1) with cyclohexadiene and dihydropyran gave the cis-fused cyclobutane 5b and the trans-fused cyclobutane 6b as major adducts, respectively. The structures including stereochemistry were established by X-ray crystallographic analysis.The results for these systems markedly contrast with those for the photocycloaddition of 1 to five-membered cycloolefins, cyclopentadiene and dihydrofuran, which yield the adducts with skeletal rearrangements. The difference of product depending on the ring size can be related to the difference in the stereochemical pathways. The distance between donor and aceeptor is suggested to be an important factor determining the polarity of the donor-acceptor pair and, therefore, the stereochemistry of the photocycloaddition.
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