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Zheng H, McDonald R, Hall DG. Boronic acid catalysis for mild and selective [3+2] dipolar cycloadditions to unsaturated carboxylic acids. Chemistry. 2010;16(18):5454-60doi: 10.1002/chem.200903484.
Zheng, H., McDonald, R., & Hall, D. G. (2010). Boronic acid catalysis for mild and selective [3+2] dipolar cycloadditions to unsaturated carboxylic acids. Chemistry (Weinheim an der Bergstrasse, Germany), 16(18), 5454-60. https://doi.org/10.1002/chem.200903484
Zheng, Hongchao, et al. "Boronic acid catalysis for mild and selective [3+2] dipolar cycloadditions to unsaturated carboxylic acids." Chemistry (Weinheim an der Bergstrasse, Germany) vol. 16,18 (2010): 5454-60. doi: https://doi.org/10.1002/chem.200903484
Zheng H, McDonald R, Hall DG. Boronic acid catalysis for mild and selective [3+2] dipolar cycloadditions to unsaturated carboxylic acids. Chemistry. 2010 May 10;16(18):5454-60. doi: 10.1002/chem.200903484. PMID: 20373314.
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Chemistry. 2010 May 10;16(18):5454-60. doi: 10.1002/chem.200903484.

Boronic acid catalysis for mild and selective [3+2] dipolar cycloadditions to unsaturated carboxylic acids.

Chemistry (Weinheim an der Bergstrasse, Germany)

Hongchao Zheng, Robert McDonald, Dennis G Hall

Affiliations

  1. Department of Chemistry, Gunning-Lemieux Chemistry Centre, University of Alberta, Edmonton, Alberta, T6G 2G2, Canada.

PMID: 20373314 DOI: 10.1002/chem.200903484

Abstract

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 ortho-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.

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