A Diastereoselective Ring Contraction of 1,3-Dioxepins to 2,3,4-Trisubstituted and Tetrasubstituted Tetrahydrofurans

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• 作者：Christopher G. Nasveschuk ; Tomislav Rovis
• 刊名：Journal of Organic Chemistry
• 出版年：2008
• 出版时间：January 18, 2008
• 年：2008
• 卷：73
• 期：2
• 页码：612 - 617
• 全文大小：188K
• 年卷期：v.73,no.2(January 18, 2008)
• ISSN：1520-6904

文摘

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A modular and diastereoselective approach to 2,3,4-trisubstituted and tetrasubstituted tetrahydrofurans isreported. The use of dioxepins containing an embedded vinyl acetal functionality leads to a Lewis acid-mediated [1,3] ring contraction to afford tetrahydrofurans in good yield and excellent diastereoselectivity.The use of TMSOTf in MeCN leads to the 2,3-cis/3,4-trans diastereomer while SnCl₄ in CH₂Cl₂ providesthe 2,3-trans/3,4-cis diastereomer. A variety of substituents are tolerated at each position. The presenceof Lewis basic functionality under the SnCl₄ conditions alters the reaction favoring the diastereomerformed under the TMSOTf conditions. We present conclusive evidence that the products of each ofthese reactions are formed under kinetic control. We further provide stereochemical models consistentwith each of these rearrangement reactions that account for the formation of the major diastereomer ineach case.