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首页> 外文期刊>Chemistry: A European journal >Boronic acid catalysis for mild and selective [3+2] dipolar cycloadditions to unsaturated carboxylic acids
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Boronic acid catalysis for mild and selective [3+2] dipolar cycloadditions to unsaturated carboxylic acids

机译：硼酸催化轻度和选择性[3 + 2]偶极环加成反应生成不饱和羧酸

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摘要

Herein, the concept of boronic acid catalysis (BAC) for the activation of unsaturated carboxylic acids is applied in several classic dipolar [3 + 2] cycloadditions involving azides, nitrile oxides, and nitrones as partners. These cycloadditions can be used to produce pharmaceutically interesting, small heterocyclic products, such as triazoles, isoxazoles, and isoxazolidines. These cycloadducts are formed directly and include a free carboxylic acid functionality that can be employed for fur-ther transformations, thereby avoiding prior masking or functionalization. In all cases, BAC provides faster reactions, under milder conditions, with much improved product yields and regioselectivities. In some instances, such as triazole formation from the reaction of azides with 2-alkynoic acids, catalysis with ort/io- nitrophenylboronic acid circumvents the undesirable product decarboxylation observed when using thermal activation. By using NMR spectroscopic studies, the boronic acid catalyst was shown to provide activation by a LUMO-lowering effect in the unsaturated carboxylic acid, likely via a monoacylated hemiboronic ester intermediate.
机译：在本文中，用于不饱和羧酸活化的硼酸催化（BAC）的概念被应用于几种经典的偶极[3 + 2]环加成反应中，其中叠氮化物，腈氧化物和硝酮为配偶体。这些环加成物可用于生产药学上感兴趣的小的杂环产物，例如三唑，异恶唑和异恶唑烷。这些环加合物是直接形成的，并且包括可用于进一步转化的游离羧酸官能度，从而避免了事先的掩蔽或官能化。在所有情况下，BAC都能在较温和的条件下提供更快的反应，并大大提高了产品收率和区域选择性。在一些情况下，例如由叠氮化物与2-链烷酸反应形成的三唑，用叔/异硝基苯基硼酸催化可避免使用热活化时观察到的不希望的产物脱羧。通过使用NMR光谱研究，表明硼酸催化剂可能通过不饱和羧酸中的LUMO降低作用提供了活化作用，很可能是通过单酰化的半硼酸酯中间体。

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