How Torsional Effects Cause Attack at Sterically Crowded Concave Faces of Bicyclic Alkenes

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• 作者：Steven A. Lopez ; Melika Pourati ; Hans-Joachim Gais ; K. N. Houk
• 刊名：Journal of Organic Chemistry
• 出版年：2014
• 出版时间：September 5, 2014
• 年：2014
• 卷：79
• 期：17
• 页码：8304-8312
• 全文大小：646K
• ISSN：1520-6904

文摘

Cycloadditions of 1,3-dipoles and related species to a cis-oxabicyclo[3.3.0]octenone occur on the more sterically crowded concave face. These cycloadditions were studied experimentally by Gais and co-workers in 1998 (Eur. J. Org. Chem. 1998, 257鈥?73) and have now been studied computationally with density functional theory (DFT). Transition states have been computed for various types of (3 + 2) cycloadditions, including diazomethane 1,3-dipolar cycloadditions, a thermally promoted methylenecyclopropane acetal cycloaddition, and a Pd-catalyzed cycloaddition of methylenecyclopropane to an oxabicyclo[3.3.0]octenone. The concave stereoselectivities arise from alkene predistortion that leads to torsional steering in the transition states.