Oxidation

doi:10.1002/3527604677.ch10

Asymmetric Organocatalysis 2005

DOI: 10.1002/3527604677.ch10

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Oxidation

Abstract: The idea of using chiral ketones as catalysts for asymmetric epoxidation of olefins was first addressed by Curci et al. in the middle of the 1980s [7]. In this initial ex-

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A Practical and Versatile Access to Dihydrosalen (Salalen) Ligands: Highly Enantioselective Titanium In Situ Catalysts for Asymmetric Epoxidation with Aqueous Hydrogen Peroxide

et al. 2007

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A modular synthesis for chiral and nonsymmetrical salalen ligands (i.e., mono-reduced salens), carrying an imine and an amine functionality has been developed. The ligands can be assembled in situ by Schiff base formation of an N-(2-hydroxybenzyl)diamine with a salicylic aldehyde, thus allowing rapid and easy variation/optimization of the ligand structure. Aiming at optimal activity and enantioselectivity in the titanium-catalyzed asymmetric epoxidation of non-functionalized olefins, a positional scanning of the two ligand halves was carried out. High epoxide yields were achieved, and up to 98 % ee. The composition of the titanium complex catalysts was determined by high resolution mass spectrometry and X-ray crystallography for one selected example.

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A Practical and Versatile Access to Dihydrosalen (Salalen) Ligands: Highly Enantioselective Titanium In Situ Catalysts for Asymmetric Epoxidation with Aqueous Hydrogen Peroxide

et al. 2007

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Mass‐Spectrometric and Kinetic Studies on the Mechanism and Degradation Pathways of Titanium Salalen Catalysts for Asymmetric Epoxidation with Aqueous Hydrogen Peroxide

2008

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The composition and degradation of a highly active and enantioselective titanium salalen in situ catalyst for the asymmetric epoxidation of olefins with aqueous hydrogen peroxide was investigated. Kinetic data and ESI-MS studies point to a monoA C H T U N G T R E N N U N G nuclear titanium salalen as the catalytically active species. By means of ESI-MS and selective monodeuteration of the salalen ligand, the oxidative degradation was studied. Upon exposure to aqueous hydrogen peroxide, the amine functionality of the salalen ligand is converted to the hydroxylamine, followed by loss of water and generation of the inactive titanium-salen complex. This transformation limits the activity of the catalyst in the epoxidation of less electron-rich olefins, such as 1-octene.

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Oxidation

Abstract: The idea of using chiral ketones as catalysts for asymmetric epoxidation of olefins was first addressed by Curci et al. in the middle of the 1980s [7]. In this initial ex-

Cited by 2 publications

References 78 publications

A Practical and Versatile Access to Dihydrosalen (Salalen) Ligands: Highly Enantioselective Titanium In Situ Catalysts for Asymmetric Epoxidation with Aqueous Hydrogen Peroxide

A Practical and Versatile Access to Dihydrosalen (Salalen) Ligands: Highly Enantioselective Titanium In Situ Catalysts for Asymmetric Epoxidation with Aqueous Hydrogen Peroxide

Mass‐Spectrometric and Kinetic Studies on the Mechanism and Degradation Pathways of Titanium Salalen Catalysts for Asymmetric Epoxidation with Aqueous Hydrogen Peroxide

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