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.
4-乙氧羰基-5-苯基-
1H-吡咯-2,3-二酮(1)与环
己二烯和二氢
吡喃的光环加成反应分别主要生成顺式融合的
环丁烷5b和反式融合的
环丁烷6b。其结构包括立体
化学通过X射线晶体学分析确定。这些体系的结果与1与五元环烯烃、
环戊二烯和二氢
呋喃的光环加成反应得到骨架重排产物的结果明显不同。根据环的大小产生不同的产物可以与立体
化学途径的差异相关。供体和受体之间的距离被认为是决定供体-受体对极性的一个重要因素,因此也是决定光环加成立体
化学的一个重要因素。