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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.

2

Karbeny N-heterocykliczne : synteza i zastosowanie

Malinowska M., Hryniewicka A.

Wiadomości Chemiczne

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2015

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[Z] 69, 3-4

227--253

EN

N-Heterocyclic carbenes (NHCs) are powerful tools in organic chemistry, with numerous applications in academic and industrial laboratories. They are usually defined as singlet carbenes, in which the divalent carbonic centre is connected directly to at least one nitrogen atom in the heterocycle [1]. They have played an important role in organic chemistry ever since the first evidence of their existence. The isolation of stable, free 1,3‑diadamantylimidazol-2-ylidene (IAd, Fig. 1) by Arduengo et al. in 1991 was a milestone in the chemistry of carbenes [2]. From the beginnings as academic curiosities, N‑heterocyclic carbenes today are very useful compounds in a variety of organic transformations (Fig. 13). NHCs are neutral σ-donors, which form very strong bonds with the majority of transition metals (stronger than phosphines). These compounds are easy-to-make ligands with great potential in homogeneous catalysis (mainly ruthenium and palladium complexes) for large number of reactions, including the coupling reactions (Heck, Negishi, Stille, Suzuki or Sonogashira reactions) and olefin metathesis [3]. Moreover, they are very useful as organocatalysts used in the benzoin condensation, the Stetter reaction and ring-opening polymerization (ROP) or transesterification [4]. In this review, we aim to give an overview of the properties and applications of NHCs, which we expect will be a useful introduction for chemists interested in studying and applying these important compounds. The first part of this review is devoted to the main synthetic routes to NHCs, their properties and reactivity. In the second part we describe the metal complexes with NHCs as homogeneous catalysts and their applications in various types of reactions. At the end of this part of the paper the use of NHCs as organocatalysts is presented.

3

Asymetryczna reakcja aldolowa: część II - katalityczna asymetryczna reakcja aldolowa w środowisku wodnym

Paradowska J., Rogozińska M., Młynarski J.

Wiadomości Chemiczne

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2010

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[Z] 64, 7-8

599-627

EN

Asymmetric organometallic and organocatalytic processes in aqueous systems are currently of great interest. A few years ago, only a few practitioners studied the subject; now organic reactions in water have become one of the most exciting research areas. Nature has perfected the stereospecific aldol reaction by using aldolase enzymes. While virtually all the biochemical aldol reactions use unmodified donor and acceptor carbonyls and take place under catalytic control in an aqueous environment, the chemical domain of the aldol addition has mostly relied on prior transformation of carbonyl substrates, and the whole process traditionally is carried out in anhydrous solvents. The area of asymmetric aldol reactions in water has received much attention recently in light of the perception of both its green chemistry advantages and its analogy to eon-perfected enzyme catalysis. Only recently catalytic asymmetric reactions promoted by water-compatible Lewis acids with chiral ligands have been developed; most Lewis acids are not stable in water. Seminal work by List, Lerner, and Barbas on the intermolecular proline-catalyzed direct asymmetric aldol reaction opened a new platform for designing metal-free asymmetric catalysts, although their application was initially limited to organic solvents. Most recently, the challenge of developing efficient aqueous-phase organocatalytic processes has also been tackled. Recent progress in the area initiated constructive discussion on the role and practical merits of water as a solvent. This article describes recent developments in this area.

4

Asymetryczna reakcja aldolowa : część I - nowe koncepcje, katalizatory i ich praktyczne zastosowanie w syntezie produktów naturalnych

Stodulski M., Młynarski J.

Wiadomości Chemiczne

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2010

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[Z] 64, 5-6

435-465

EN

The aldol reaction is one of the most important method for the stereoselective construction of polyketide natural products in both – living organisms and laboratory. The tremendous development in this field has led to development of many new variants of the aldol addition. There has been some success in the use of asymmetric catalysts, although they normally rely on a Mukaiyama-type process. This reaction required a conversion of a donor substrate into more reactive species such as enol silyl ether using not less than stoichiometric amounts of a silicon reagent and a base. From atom economic perspectives, such stoichiometric amounts of reagents should be excluded from the procedures. An exciting challenge in enhancement of the efficiency of the aldol reaction is to find a compound that will catalyze direct aldol addition without pre-formation of a nucleophile and to do so asymmetrically. Direct asymmetric aldol reaction, catalyzed by both metallic complexes and purely organic molecules now becomes one of the most desired tools in organic chemistry. After an initial period of validating methodology by using a wide range of important model reactions, the time has now been reached to address specific synthesis and solve pending problems of practical relevance. In this review we describe recently discovered, most important and most flexible catalysts for direct asymmetric aldol reaction and their application in total synthesis of target natural products and known compounds of biological and pharmaceutical relevance.

5

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.