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Addition of Azomethine Ylides to Aldehydes: Mechanistic Dichotomy of Differentially Substituted alpha-Imino Esters
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
2010 (English)In: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, no 20, 3927-3933 p.Article in journal (Refereed) Published
Abstract [en]

The formal 1,3-dipolar cycloaddition of azomethine ylides and aldehydes is explored, as hydrolysis of the resulting oxazolidine product gives facile access to valuable syn-beta-aryl-beta-hydroxy-alpha-amino esters. The use of using benzaldehyde-derived imines as the ylide precursor results in 1,3-dipolar cycloaddition with high conversions but low diastereoselectivity. In contrast, the employment of benzophenone-derived imines as the ylide precursor results in an aldol reaction, which gives the intermediate oxazolidine in high diastereoselectivity and requires a weak acid catalyst to achieve higher conversions.

Place, publisher, year, edition, pages
2010. no 20, 3927-3933 p.
Keyword [en]
Amino alcohols, Azomethine ylides, Aldol reaction, Cycloaddition
National Category
Organic Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-29445DOI: 10.1002/ejoc.201000377ISI: 000280428700019Scopus ID: 2-s2.0-77954263292OAI: oai:DiVA.org:kth-29445DiVA: diva2:397050
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council
Note
QC 20110211Available from: 2011-02-11 Created: 2011-02-02 Last updated: 2017-12-11Bibliographically approved
In thesis
1. New Methods for the Synthesis of Vicinal Stereocenters: Palladium-Catalyzed Domino Reactions and Asymmetric Transfer Hydrogenation
Open this publication in new window or tab >>New Methods for the Synthesis of Vicinal Stereocenters: Palladium-Catalyzed Domino Reactions and Asymmetric Transfer Hydrogenation
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis the synthesis of vicinal stereocenters is investigated in two distinct contexts, namely the construction of 3,3-disubstituted oxindoles and the synthesis of b-hydroxy-a-amino acids. Both scaffolds are prevalent in a range of natural products and biologically relevant compounds and, therefore, methods for their synthesis are of great import.

First, the construction of 3,3-disubstituted oxindoles using palladium-catalyzed domino reactions is described.  This covers two stereospecific methods for the construction of the desired oxindoles based on domino carbopalladation sequences.  The termination events for these domino reactions are carbonylation or cross-coupling.  In the carbopalladation-carbonylation reaction, we studied the possibilty of suppressing b-hydride elimination for substrates possessing pendant b-hydrogens.  In the carbopalladation-cross-coupling sequence, we examined the role of the boron source and substrate scaffold in the outcome of the reaction.  In both of these methods, an intricate balance of rates needs to be attained in order to achieve the desired domino sequences.  Thus, these investigations offer insight into the rates of the competing reactions, and the factors that influence these processes.

Secondly, the stereoselective synthesis of b-hydroxy-a-amino acids is explored.  This has lead to two separate methods for the construction of this scaffold.  We first examined a 1,3-dipolar cycloaddition of azomethine ylides to aldehydes for the construction of syn-b-hydroxy-a-amino esters.  It was found that one set of azomethine ylides reacted through a 1,3-dipolar cycloaddition, while the other set reacted via a direct aldol reaction.  Finally, we studied an asymmetric transfer hydrogenation reaction to provide anti-b-hydroxy-a-amido esters from the corresponding a-amido-b-ketoesters.  Two protocols were developed for the reduction of these substrates, one using triethylammonium formate and the other using sodium formate in an emulsion.  The latter method gives high yields, diastereoselectivities and enantioselectivities for a broad range of substrates.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. 75 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2012:27
Keyword
asymmetric synthesis, domino reactions, palladium-catalyzed reactions, oxindoles, amino alcohols
National Category
Natural Sciences Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-95327 (URN)978-91-7501-374-9 (ISBN)
Public defence
2012-08-17, F3, Linstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20120605Available from: 2012-06-05 Created: 2012-05-22 Last updated: 2012-06-05Bibliographically approved

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