Intramolecular [2 + 2] Photocycloaddition/Thermal Fragmentation: Formally "Allowed" and "Forbidden" Pathways toward 5-8-5 Ring Systems

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• 作者：Scott J. Bader and Marc L. Snapper
• 刊名：Journal of the American Chemical Society
• 出版年：2005
• 出版时间：February 2, 2005
• 年：2005
• 卷：127
• 期：4
• 页码：1201 - 1205
• 全文大小：131K
• 年卷期：v.127,no.4(February 2, 2005)
• ISSN：1520-5126

文摘

The thermal fragmentation of highly functionalized, linear polycyclobutanes with a cis,syn,cis-relative stereochemistry is shown to offer a rapid entry into the dicyclopenta[a,d]cyclooctenyl (5-8-5) ringsystem. The thermolysis of polyfused cyclobutanes with a cis,syn,cis- or a cis,anti,cis-relationship proceedsin a formally "symmetry-allowed" manner through the intermediacy of a cis,trans-cyclooctadiene. When abridging tether used to establish the cis,syn,cis-stereochemistry in the intramolecular [2 + 2] photocyclizationis present in the thermolysis step, however, the result of a formally "symmetry-forbidden" fragmentation isobserved yielding cis,cis-cyclooctadiene-containing 5-8-5 products. In general, the stereochemicalobservations noted in these fragmentations offer new opportunities for accessing a variety of stereochemicalrelationships in these 5-8-5 ring systems.