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Origin of Enantioselectivity in the Organocatalytic Reductive Amination of α-Branched Aldehydes
KTH, School of Biotechnology (BIO), Theoretical Chemistry. (Theoretical Chemistry)
KTH, School of Biotechnology (BIO), Theoretical Chemistry. (Theoretical Chemistry)
KTH, School of Biotechnology (BIO), Theoretical Chemistry. (Teoretical Chemistry)
2009 (English)In: Advanced Synthesis and Catalysis, ISSN 1615-4150, E-ISSN 1615-4169, Vol. 351, no 4, 525-529 p.Article in journal (Refereed) Published
Abstract [en]

The reason for enantioselectivity in thereductive amination of α-branched aldehydes wasinvestigated. The relative energies of all the diastereomeric transition states for hydride transfer of a suitable computational model were calculated at the B3LYP/6-311+(2d,2p) level of theory. Our calculations successfully reproduce and rationalize the experimentally observed stereochemical outcome of the reaction.

Place, publisher, year, edition, pages
Weinheim: Wiley-VCH Verlag GmbH&Co. KGaA , 2009. Vol. 351, no 4, 525-529 p.
Keyword [en]
density functional theory; dynamic kinetic resolution; Hantzsch esters; organocatalysis; reduction
National Category
Theoretical Chemistry Organic Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-11612DOI: 10.1002/adsc.200800613ISI: 000264831500003Scopus ID: 2-s2.0-62549085227OAI: oai:DiVA.org:kth-11612DiVA: diva2:278324
Note
QC 20100719Available from: 2009-11-25 Created: 2009-11-25 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Quantum Chemical Studies of Mechanisms and Stereoselectivities of Organocatalytic Reactions
Open this publication in new window or tab >>Quantum Chemical Studies of Mechanisms and Stereoselectivities of Organocatalytic Reactions
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

As the field of organocatalysis is growing, it is becoming more important to understand the specific modes of action of these new organic catalysts. Quantum chemistry, in particular density functional theory, has proven very powerful in exploring reaction mechanisms as well as selectivities in organocatalytic reactions, and is the tool used in this thesis. Different reaction mechanisms of several organocatalytic reactions have been examined, and we have been able to exclude various reaction pathways based on the calculated reaction barriers. The origins of stereoselection in a number of reactions have been rationalized. The computational method has generally reproduced the experimental stereoselectivities satisfactorily.

The amino acid-catalyzed aldol reaction has previously been established to go through an enamine intermediate. In the first study of this thesis the understanding of this kind of reactions has been expanded to the dipeptide-catalyzed aldol reaction. The factors governing the enantioselection have been studied, showing how the chirality of the amino acids controls the conformation of the transition state, thereby determining the configuration of the product.

In the cinchona thiourea-catalyzed Henry reaction two reaction modes regarding substrate binding to the two sites of the catalyst have been investigated, showing the optimal arrangement for this reaction. This enabled the rationalization of the observed stereoselectivity.

The hydrophosphination of α,β-unsaturated aldehydes was studied. The bulky substituent of the chiral prolinol-derived catalyst was shown to effectively shield one face of the reactive iminium intermediate, thereby inducing the stereoselectivity.

The transfer hydrogenation of imines using Hantzsch esters as hydride source and axially chiral phosphoric acid catalyst has also been explored. A reaction mode where both the Hantzsch ester and the protonated imine are hydrogen bonded to the phosphoric acid is demonstrated to be the preferred mode of action. The different arrangements leading to the two enantiomers of the product are evaluated for several cases, including the hydride transfer step in the reductive amination of α-branched aldehydes via dynamic kinetic resolution.

Finally, the intramolecular aldol reaction of ketoaldehydes catalyzed by guanidinebased triazabicyclodecene (TBD) has been studied. Different mechanistic proposals have been assessed computationally, showing that the favoured reaction pathway is catalyzed by proton shuttling. The ability of a range of guanidines to catalyze this reaction has been investigated. The calculated reaction barriers reproduced the experimental reactivities quite well.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. viii, 72 p.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2009:27
National Category
Theoretical Chemistry Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-11616 (URN)978-91-7415-498-6 (ISBN)
Public defence
2009-12-18, Svedbergsalen, FD5, Roslagstullsbacken 21, AlbaNova, Stockholm, 14:00 (English)
Opponent
Supervisors
Note
QC 20100719Available from: 2009-12-04 Created: 2009-11-25 Last updated: 2011-11-23Bibliographically approved

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