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Highly efficient redox isomerization of allylic alcohols at ambient temperature catalyzed by novel ruthenium cyclopentadienyl complexes: New insight into the mechanism
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Stockholm University, Faculty of Science, Department of Organic Chemistry.
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2005 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 11, no 20, 5832-5842 p.Article in journal (Refereed) Published
Abstract [en]

A range of ruthenium cyclopentadienyl (Cp) complexes have been prepared and used for isomerization of allylic alcohols to the corresponding saturated carbonyl compounds. Complexes bearing CO ligands show higher activity than those with PPh3 ligands. The isomerization rate is highly affected by the substituents on the Cp ring. Tetra(phenyl)methyl-substituted catalysts rapidly isomerize allylic alcohols under very mild reaction conditions (ambient temperature) with short reaction times. Substituted allylic alcohols have been isomerized by employing Ru–Cp complexes. A study of the isomerization catalyzed by [Ru(Ph5Cp)(CO)2H] (14) indicates that the isomerization catalyzed by ruthenium hydrides partly follows a different mechanism than that of ruthenium halides activated by KOtBu. Furthermore, the lack of ketone exchange when the isomerization was performed in the presence of an unsaturated ketone (1 equiv), different from that obtained by dehydrogenation of the starting allylic alcohol, supports a mechanism in which the isomerization takes place within the coordination sphere of the ruthenium catalyst.

Place, publisher, year, edition, pages
Wiley , 2005. Vol. 11, no 20, 5832-5842 p.
Keyword [en]
allylic compounds;hydrides;isomerization;mechanism elucidation;ruthenium
National Category
Organic Chemistry
URN: urn:nbn:se:su:diva-23893DOI: 10.1002/chem.200500490OAI: diva2:195181
Part of urn:nbn:se:su:diva-537Available from: 2005-05-13 Created: 2005-05-13 Last updated: 2010-10-04Bibliographically approved
In thesis
1. Ruthenium-catalyzed redox reactions and lipase-catalyzed asymmetric transformations of alcohols
Open this publication in new window or tab >>Ruthenium-catalyzed redox reactions and lipase-catalyzed asymmetric transformations of alcohols
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The major part of this thesis describes the synthesis of enantiopure alcohols and diols by combining ruthenium-catalyzed redox reactions that lead to racemization or epimerization and lipase-catalyzed asymmetric trans-formations in one-pot.

A mechanistic study of the unexpected facile formation of meso-diacetate products found in enzyme-catalyzed acetylations of alkanediols with Candida antarctica lipase B (CALB) was first performed. By deuterium labeling it was found that the formation of meso-diacetates proceeds via different mechanisms for 2,4-pentanediol and 2,5-hexanediol. Whereas the first reacts via an intramolecular acyl migration, the latter proceeds via a direct, anomalous S-acylation of the alcohol. The acyl migration occurring in the 2,4-pentanediol monoacetate was taken advantage of in asymmetric transformations of substituted 1,3-diols by combining it with a ruthenium-catalyzed epimerization and an enzymatic transesterification using CALB. The in situ coupling of these three processes results in de-epimerization and deracemization of acyclic, unsymmetrical 1,3-diols and constitutes a novel dynamic kinetic asymmetric transformation (DYKAT) concept.

Racemization of secondary alcohols effected by a new ruthenium complex was combined in one-pot with an enzyme-catalyzed transesterification, leading to a chemoenzymatic dynamic kinetic resolution (DKR) operating at room temperature. Aromatic, aliphatic, heterocyclic and functionalized alcohols were subjected to the procedure. A mechanism for racemization by this ruthenium complex has been proposed and experimental indications for hydrogen transfer within the coordination sphere of ruthenium were found. The same ruthenium catalyst was used for epimerization in DYKAT of 1,2-diols, and a very similar complex was employed in isomerization of allylic alcohols to saturated ketones. The former method is a substrate extension of the above principle applied for DYKAT of 1,3-diols. The combination of a lipase and an organocatalyst was demonstrated by linking a lipase-catalyzed transesterification to a proline-mediated aldol reaction for the production of enantiopure (S)-β-hydroxy ketones and acetylated (R)-aldols.

Place, publisher, year, edition, pages
Stockholm: Institutionen för organisk kemi, 2005
ruthenium, lipase, catalysis, alcohols, diols
National Category
Chemical Sciences
urn:nbn:se:su:diva-537 (URN)91-7155-053-4 (ISBN)
Public defence
2005-06-10, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 16:15
Available from: 2005-05-13 Created: 2005-05-13Bibliographically approved

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Martín-Matute, BelénBäckvall, Jan-E.
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