Univerzita Pardubice Fakulta chemicko- technologická

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Asymmetric Sharpless epoxidation catalysed by polystyrene-supported tartrate

Autoři: Sedlák Miloš | Bartáček Jan | Drabina Pavel | Váňa Jiří

Rok: 2018

Druh publikace: ostatní - přednáška nebo poster

Strana od-do: nestránkováno

Tituly:

Jazyk	Název	Abstrakt	Klíčová slova
eng	Asymmetric Sharpless epoxidation catalysed by polystyrene-supported tartrate	The Sharpless asymmetric epoxidation is one of the earliest known methods of the enantioselective synthesis. The reaction involves a stereoselective oxygen-transfer from organic hydroperoxides to allylic alcohols’ double bond, catalysed by chiral titanium (IV) complexes of enantiopure tartaric acid derivatives (predominantly esters) [1]. The resulting products, 2-hydroxymethyloxiranes, are important intermediates in the synthesis of many perspective compounds [2]. The enantiomeric excess is excellent for various substrates. However, there are still some difficulties with the synthesis. One of them is the need of the alkaline aqueous workup to decompose the titanium (IV) complex, which can be problematic for labile epoxides. The second major problem is the possibly difficult separation of the catalyst residues from the product [3]. These synthesis issues can be resolved by preparing a pearl-like copolymer of tartrate ligand with styrene, which can be easily filtered off after the reaction without the need of the catalysis complex decomposition or further separation from the product. A novel molecule suitable for polymerization with tartrate moiety, ethyl(4-vinylbenzyl)-L-tartrate, was prepared. Several different pearl-like copolymers with different tartrate/styrene ratio were prepared by suspension copolymerization. The prepared copolymers were in situ complexed with titanium (IV) isopropoxide and the catalytic activity was tested on a model epoxidation of allylic alcohols with tert-butyl hydroperoxide at –25 °C. The results obtained (up to 99% conversion and >99% ee) in terms of enantioselectivity are comparable to the homogenous catalyst. The conversion achieved is even better than under homogeneous conditions [4].	Sharpless epoxidation; allylic alcohols; polymerization; ethyl(4-vinylbenzyl)-L-tatrate