| Lewis Acid Catalysed Reactions of Chiral Imidazolidinones and Oxazolidinones: Insights on the Role of the Catalyst. | |
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MedLine Citation:
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PMID: 21786834 Owner: NLM Status: Publisher |
Abstract/OtherAbstract:
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The mechanism proposed by Evans to justify the selectivity obtained in Lewis acid catalysed Diels-Alder reactions of cyclopentadiene with acyloxazolidinones has been generalized and used in the rationalization of selectivities obtained in many other systems. However, we recently proposed an alternative mechanism, on the basis of open-chain mono and bicomplexes, that avoids the need for chelates and explains the selectivity obtained by Evans. In this manuscript we apply our proposal to the catalysed conjugated addition of amines to acylimidazolidinones, reported by Cardillo, and we clearly show that aluminium chelates are not involved in the reaction, as they induce no selectivity, while Cardillo observed high experimental selectivities. Our data equally show that bicomplexes with carbonyl parallel orientation, proposed by Cardillo to justify the experimental selectivity with non-chelating Lewis acids, indeed induce the opposite selectivity and have also to be dismissed. On the other hand, our mechanistic proposal allows for the full rationalization of the data obtained by Cardillo with aluminium, boron or zinc Lewis acids, and supports our previous proposal on DA cycloadditions of dienes to Evans chiral auxiliary derivatives. |
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Authors:
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Filipe J S Duarte; Snezhana M Bakalova; Eurico J Cabrita; António Gil Santos |
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Publication Detail:
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Type: JOURNAL ARTICLE Date: 2011-7-26 |
Journal Detail:
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Title: The Journal of organic chemistry Volume: - ISSN: 1520-6904 ISO Abbreviation: - Publication Date: 2011 Jul |
Date Detail:
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Created Date: 2011-7-26 Completed Date: - Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 2985193R Medline TA: J Org Chem Country: - |
Other Details:
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Languages: ENG Pagination: - Citation Subset: - |
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From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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