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环状腈类:立体发散性加成-烷基化-环化反应合成顺式和反式枞烷类化合物

Cyclic nitriles: stereodivergent addition-alkylation-cyclization to cis- and trans-abietanes.

作者信息

Fleming Fraser F, Wei Guoqing, Steward Omar W

机构信息

Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA 15282-1530, USA.

出版信息

J Org Chem. 2008 May 16;73(10):3674-9. doi: 10.1021/jo8001062. Epub 2008 Apr 17.

Abstract

Diverse cyclic hydroxy nitriles are readily synthesized through sequential 1,2-1,4-Grignard addition-methylations to 3-oxo-1-cyclohexene-1-carbonitrile. Acid-catalyzed intramolecular cyclizations of the cyclic hydroxy nitriles reveal fundamental stereoselectivity trends in Friedel-Crafts cyclizations to cis- and trans-abietanes. In contrast to previous assumptions, comparative cationic cyclizations with electron-rich and electron-poor aromatic nucleophiles exhibit similar preferences for cyclization to cis-abietanes. Optimizing the cyclizations for trans-abietanes has identified ZrCl 4 as an exceptional Lewis acid which, for cyclizations of iminolactones, favors trans-abietanes as the only observable diastereomer. The sequential oxonitrile addition-Friedel-Crafts cyclization strategy provides a rapid, stereodivergent synthesis of cis- or trans-abietanes, demonstrates the dramatic influence of ZrCl 4 in promoting cationic cyclizations, and in contrast to previous assumptions suggests that the cyclization stereoselectivity is not correlated with the electronic nature of the aromatic nucleus.

摘要

通过对3-氧代-1-环己烯-1-腈进行连续的1,2-1,4-格氏加成-甲基化反应,可以轻松合成多种环状羟基腈。环状羟基腈的酸催化分子内环化反应揭示了傅克环化反应生成顺式和反式枞酸型二萜类化合物的基本立体选择性趋势。与之前的假设相反,用富电子和贫电子芳香亲核试剂进行的比较阳离子环化反应对生成顺式枞酸型二萜类化合物表现出相似的环化偏好。对反式枞酸型二萜类化合物的环化反应进行优化后发现,ZrCl₄是一种特殊的路易斯酸,对于亚胺内酯的环化反应,它有利于生成反式枞酸型二萜类化合物作为唯一可观察到的非对映异构体。连续的氧腈加成-傅克环化策略提供了一种快速、立体发散的顺式或反式枞酸型二萜类化合物的合成方法,证明了ZrCl₄在促进阳离子环化反应中的显著影响,并且与之前的假设相反,表明环化立体选择性与芳香核的电子性质无关。

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