Asymmetric 1,4-addition of oxazolones to nitroalkenes by bifunctional cinchona alkaloid thiourea organocatalysts: synthesis of alpha,alpha-disubstituted alpha-amino acids |
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Authors: | Alemán José Milelli Andrea Cabrera Silvia Reyes Efraim Jørgensen Karl Anker |
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Affiliation: | Danish National Research Foundation Center for Catalysis, Department of Chemistry, Aarhus University, 8000 Aarhus C, Denmark. |
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Abstract: | An easy and simple synthetic approach to optically active alpha,alpha-quaternary alpha-amino acids using asymmetric organocatalysis is presented. The addition of oxazolones to nitroalkenes catalyzed by thiourea cinchona derivatives provides the corresponding alpha,alpha-quaternary alpha-amino acid derivatives with good yields, excellent diastereoselectivities (up to 98 % dr), and from moderate to good enantioselectivities (up to 92 % ee). The reaction can be performed on a large scale. The optically active oxazolone-nitroalkene addition products can be opened in a one-pot reaction to the corresponding ester-amide derivatives. Additional transformations are also presented, such as the synthesis of amino esters, amino acids, and transformation into 3,4-disubstituted pyrrolidin-2-ones. |
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Keywords: | amino acids organocatalysis oxazolones thiourea |
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