期刊
TETRAHEDRON
卷 71, 期 52, 页码 9645-9661出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.tet.2015.10.064
关键词
Multicomponent; Cycloaddition; Azomethine ylide; Pyrrolizidines; Prolines
资金
- Spanish Ministerio de Ciencia e Innovacion (MICINN) [CTQ2010-20387, CSD2007-00006]
- Spanish Ministerio de Economia y Competitividad (MINECO) [CTQ2013-43446-P, CTQ2014-51912-REDC]
- FEDER
- Generalitat Valenciana [PROMETEO 2009/039, PROMETEOII/2014/017]
- University of Alicante
- Spanish Government
A general synthesis of highly substituted pyrrolizidines can be performed by a multicomponent 1,3-dipolar cycloaddition using proline ester hydrochlorides, aldehydes and dipolarophiles, at room temperature without catalysts or in the presence of AgOAc (5 mol %). In the case of (2S,4R)-4-hydroxyproline derivatives it is possible to obtain enantioenriched pyrrolizidines with high control of the regio- and diastereoselectivity affording the adducts 2,4-trans-2,5-trans according to an endo-approach and a S-dipole geometry of the in situ generated azomethine ylide. For proline esters a similar regioselectivity and endo-diastereoselectivity are observed when the dipole promotes an a-attack. However, when ethyl glyoxylate is used as aldehyde component the gamma-attack of the S-ylide takes place preferentially giving rise the opposite regioselectivity for acrylic dipolarophiles, being crucial the role of silver acetate. In this case, the exo-adducts with a 2,3-cis-2,5-trans relative configuration are diastereoselectively obtained. In addition, computational studies have also been carried out to shed light on the origins of the diastereo- and regioselectivity observed for the described 1,3-dipolar cycloadditions. (C) 2015 Elsevier Ltd. All rights reserved.
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