Wyniki wyszukiwania - BazTech

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Profesor Henryk Krawczyk – wspomnienia

Albrecht Ł.

Eliksir

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2018

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nr 1

5--6

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Nowe technologie w asymetrycznej syntezie α,α-dipodstawionych α-aminokwasów

Hejmanowska J., Albrecht Ł.

Technical Issues

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2016

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nr 2

11--17

EN

Optically active α,α-disubstituted α-amino acids represent a privileged structural motif present in numerous natural products and pharmacologically active molecules. These compounds have interesting biological properties owing to the presence of the quaternary stereogenic center. In recent years intensive development of methods for the synthesis of α,α-disubstituted α-amino acids has been observed. Azlactones constitute an important group of quaternary amino acid precursors that have found widespread application in organic synthesis. The aim of our work was to develop a new enantioselective methods for the synthesis α,α-disubstituted α-amino acids containing either geminal bisphosphonate, 3,4-dihydrocoumarin or tetrahydrothiophene moiety. Michael addition constitutes a key step in the developed synthetic strategies. The reactions were performed under basic conditions, using cinchona alkaloid derivatives with the proposed synthetic technologies being highly stereoselective.

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Chiralne katalizatory organiczne w asymetrycznej reakcji Michaela

Albrecht Ł., Krawczyk H.

Wiadomości Chemiczne

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2009

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[Z] 63, 5-6

391-436

EN

In marked contrast to enantioselective Michael reactions promoted by chiral Lewis acids, organocatalytic Michael reactions have not been used as standard transformation in organic chemistry until quite recently. During the past few years chiral organocatalysts have emerged as a broadly applicable class of catalysts for enantioselective Michael reaction. This review summarizes these advances emphasizing the structural and mechanistic features that contribute to high enantioselectivity in organocatalytic Michael reactions. The first part of this review deals with the development of covalent catalysis in organocatalytic asymmetric Michael reactions. To date, several chiral secondary amines have been employed to promote formation of electron-rich enamines from enolizable aldehydes and ketones, which then react with various ?,?-unsaturated electrophiles to afford products [7-24]. In contrast, chiral imidazolidinones and diarylprolinol ethers are most often used to activate ?,?-unsaturated carbonyl compounds by forming electron-deficient iminium ions, which render the ?-carbon more electrophilic then their carbonyl precursors for nucleophilic attack [2a, 7, 25-34]. The second part of this review documents the development of non-covalent catalysis [35-64]. In this regard, chiral Bronstedt bases [35-39], chiral phase-transfer catalysts [40-49] and chiral hydrogen-bond donors [50-64] have emerged in the past few years as readily accessible organocatalysts of asymmetric Michael reaction. The most efficient catalysts such as cinchona alkaloids and their derivatives, quaternary ammonium salts obtained from cinchona alkaloids and chiral thiourea derivatives, respectively are revived and the modes of actions are discussed. Furthermore, the major developments of organocatalytic asymmetric Michael reactions are also reviewed.