Efficient ball-mill procedure in the ‘green’ asymmetric aldol reaction organocatalyzed by (S)-proline-containing dipeptides in the presence of water |
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Authors: | José G HernándezEusebio Juaristi |
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Institution: | Departamento de Química, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Apartado Postal 14-740, 07000 México D.F., Mexico |
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Abstract: | The organocatalytic activity of (S)-proline-based dipeptides 1a-c has been evaluated in the asymmetric aldol reaction between representative ketones with various aromatic aldehydes under solvent-free conditions in a ball mill. In particular, the methyl ester of (S)-proline-(S)-tryptophan, (S,S)-1c, proved to be an efficient organocatalyst, and the aldol reaction proceeded with good chemical yields and excellent diastereo- and enantioselectivity (up to 98:2 anti/syn dr and up to 98% ee), in the presence of water, and 5 mol % of benzoic acid as additive. |
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Keywords: | Chiral dipeptides Organocatalysis Ball-milling Green chemistry Asymmetric aldol reaction |
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