Boronic Acid Catalysis for Mild and Selective [3+2] Dipolar Cycloadditions to Unsaturated Carboxylic Acids
書誌事項
- 公開日
- 2010-05-04
- 権利情報
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- http://onlinelibrary.wiley.com/termsAndConditions#vor
- DOI
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- 10.1002/chem.200903484
- 公開者
- Wiley
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説明
<jats:title>Abstract</jats:title><jats:p>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 further 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 <jats:italic>ortho</jats:italic>‐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.</jats:p>
収録刊行物
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- Chemistry – A European Journal
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Chemistry – A European Journal 16 (18), 5454-5460, 2010-05-04
Wiley
