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首页> 外文期刊>Chemistry: A European journal >Synthesis of 2-isoxazolines: Enantioselective and racemic methods based on conjugate additions of oximes
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Synthesis of 2-isoxazolines: Enantioselective and racemic methods based on conjugate additions of oximes

机译：2-异恶唑啉的合成：基于肟的共轭加成的对映选择性和外消旋方法

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摘要

The formation of 3-unsubstituted 2-isoxazolines by means of condensation reactions between α,β-unsaturated aldehydes and oximes proceeds readily in the presence of catalytic amounts of anilinium salts. Mechanistically, the process involves a fast conjugate addition of the oxime and a slower intramolecular oxime-transfer reaction. The rate of oxime transfer was found to correlate with the acidity of the catalyst. This finding enabled us to discover an enantioselective process in which the fragile conjugate-addition product generated in the first stage is rapidly cyclized into the stable isoxazo-line under acidic conditions, with conservation of enantiomeric excess. In summary, herein we describe synthetically useful protocols for accessing 3-unsubstituted 2-isoxazolines in both the enantioselective and racemic manner. The mechanism of the condensation reaction catalyzed by the anilinium salt was also investigated by NMR spectroscopy experiments in which the effect of differently substituted aldehydes and oximes as well as water on the reaction rate was studied. The results point to the rate-limiting elimination of water from the 3-hydroxy-2-iso-xazolidine intermediate.
机译：通过α，β-不饱和醛和肟之间的缩合反应形成3-未取代的2-异恶唑啉在催化量的苯胺盐存在下容易进行。从机理上讲，该过程涉及快速共轭添加肟和较慢的分子内肟转移反应。发现肟转移的速率与催化剂的酸度相关。该发现使我们能够发现对映选择性过程，其中在酸性条件下，在第一阶段产生的易碎的缀合物加成产物快速环化成稳定的异恶唑啉，同时保留了对映体过量。总而言之，本文中我们描述了以对映选择性和外消旋两种方式获得3-未取代的2-异恶唑啉的合成有用的方案。还通过NMR光谱实验研究了由苯胺盐催化的缩合反应的机理，其中研究了不同取代的醛和肟以及水对反应速率的影响。结果表明从3-羟基-2-异-恶唑烷中间体中限速消除水。

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