The Experts below are selected from a list of 264 Experts worldwide ranked by ideXlab platform
Péter Bakó - One of the best experts on this subject based on the ideXlab platform.
-
Synthesis of xylal- and arabinal-based crown ethers and their application as asymmetric phase transfer catalysts.
Chirality, 2019Co-Authors: Tamás Nemcsok, Zsolt Rapi, György Keglevich, Péter Bagi, Péter BakóAbstract:: New xylal- and arabinal-based monoaza-15-crown-5 ethers were synthesized starting from l- and d-xylose, and l- and d-arabinose, respectively. These monosaccharide-based chiral macrocycles were tested as phase transfer catalysts in a few asymmetric reactions. The xylal-based crown compounds proved to be efficient catalysts in a few liquid-liquid phase reactions. The epoxidation of trans-chalcone and the Darzens Condensation of α-chloroacetophenone with benzaldehyde took place with complete diastereoselectivity and up to 77% ee and 58% ee, respectively. It was found that the substituents in the aromatic ring of the chalcone and the α-chloroacetophenone had an influence on the enantioselectivity. The highest ee values were obtained in the epoxidation of 4-chlorochalcone (81% ee) and in the reaction of a 2-naphthyl analogue (96% ee), while in the Darzens Condensation of 4-phenyl-α-chloroacetophenone with benzaldehyde, a maximum ee of 91% was detected. The configuration of the monosaccharide unit in the crown ring influenced the absolute configuration of the epoxyketones synthesized.
-
Synthesis of chiral crown ethers derived from D-galactose and their application in enantioselective reactions
Tetrahedron, 2019Co-Authors: Zsolt Rapi, Tamás Nemcsok, György Keglevich, Péter Bagi, Péter BakóAbstract:Abstract A few new α- and β- d -galactopyranoside-based chiral lariat ethers of monoaza-15-crown-5 type were synthesized. These macrocycles proved to be efficient catalysts in a few asymmetric reactions under mild phase transfer conditions. The catalytic effect of the lariat ethers with methoxy, ethoxy, isopropoxy and aryloxy substituents on the C-1 of the sugar unit in both α and β positions was compared. In the presence of β- d -galactopyranoside-based crown ethers, the asymmetric Darzens Condensation of α-chloroacetophenone and benzaldehyde, the epoxidation of trans -chalcone, the cyclopropanation (MIRC reaction) of benzylidenemalononitrile and 2-benzylidene-1,3-indandione with diethyl bromomalonate were performed with enantioselectivities of 61%, 64%, 86% and 96%, respectively. In all reactions, the β-anomers were more efficient in terms of enantioselectivity than the α forms.
-
Synthesis of d-mannitol-based crown ethers and their application as catalyst in asymmetric phase transfer reactions.
Chirality, 2017Co-Authors: Tamás Nemcsok, Zsolt Rapi, György Keglevich, Alajos Grün, Péter BakóAbstract:: A few new d-mannitol-based monoaza-15-crown-5 type chiral lariat ethers and 18-crown-6 type macrocycles were synthesized. These crown compounds were used as phase transfer catalysts in asymmetric Michael addititons and in a Darzens Condensation under mild conditions to afford the corresponding products in a few cases in good to excellent enantioselectivities. In the Michael addition of diethyl acetoxymalonate to trans-chalcone, in the addition of diethyl acetamidomalonate to s-nitrostyrene, in the reaction of diethyl bromomalonate with benzylidene malononitriles, in the cyclopropanation reaction of diethyl bromomalonate and 2-benzylidene-1,3-indandione, and in the Darzens Condensation of α-chloroacetophenone with benzaldehyde, maximum enantioselectivities of 39%, 65%, 99%, 56%, and 62%, respectively, were obtained in the presence of the d-mannitol-based macrocycles as the catalysts.
-
Sugar-based Crown Ethers in Enantioselective Syntheses
Periodica Polytechnica Chemical Engineering, 2015Co-Authors: Péter Bakó, Zsolt Rapi, György KeglevichAbstract:A number of chiral macrocyclic compounds have been prepared that contain a monosaccharide-derived sub-unit. These sugar-based crown ethers were used as chiral phase transfer catalysts in a few asymmetric reactions. A few of them proved to be effective catalysts in Michael additions, a Darzens Condensation and an epoxidation of α,β-enones. It was found that the type of the monosaccharide, the substituents on the sugar unit and on the nitrogen atom of the macroring have a significant influence on both the yield and the enantioselectivity.
-
Side‐Arm Effect of a Methyl α‐d‐Glucopyranoside Based Lariat Ether Catalysts in Asymmetric Syntheses
Heteroatom Chemistry, 2014Co-Authors: Zsolt Rapi, Péter Bakó, László Drahos, György KeglevichAbstract:Methyl α-d-glucopyranoside based monoaza-15-crown-5 type lariat ethers with different heteroatom-containing side arm attached to the nitrogen of the macrocyclic ring have been synthesized. These compounds were used as chiral phase transfer catalysts in a few asymmetric reactions, such as Michael additions, Darzens Condensation, and epoxidation of chalcone. The side arms of the macrocycles had a significant impact on the chemical yields and the enantioselectivity. The effect of the lariat ethers with side arms having heteroatom (O, N, and S) was compared with the effect of the analogues having substituents without a heteroatom. The terminal allyl group also generated a significant enantioselectivity (79% enantiomeric excess) in one of the Michael additions. The application of crown ethers with substituents (CH2)3OH or (CH2)3OCH3 leads to the best enantioselectivities 85% and 99%, respectively.
György Keglevich - One of the best experts on this subject based on the ideXlab platform.
-
Synthesis of xylal- and arabinal-based crown ethers and their application as asymmetric phase transfer catalysts.
Chirality, 2019Co-Authors: Tamás Nemcsok, Zsolt Rapi, György Keglevich, Péter Bagi, Péter BakóAbstract:: New xylal- and arabinal-based monoaza-15-crown-5 ethers were synthesized starting from l- and d-xylose, and l- and d-arabinose, respectively. These monosaccharide-based chiral macrocycles were tested as phase transfer catalysts in a few asymmetric reactions. The xylal-based crown compounds proved to be efficient catalysts in a few liquid-liquid phase reactions. The epoxidation of trans-chalcone and the Darzens Condensation of α-chloroacetophenone with benzaldehyde took place with complete diastereoselectivity and up to 77% ee and 58% ee, respectively. It was found that the substituents in the aromatic ring of the chalcone and the α-chloroacetophenone had an influence on the enantioselectivity. The highest ee values were obtained in the epoxidation of 4-chlorochalcone (81% ee) and in the reaction of a 2-naphthyl analogue (96% ee), while in the Darzens Condensation of 4-phenyl-α-chloroacetophenone with benzaldehyde, a maximum ee of 91% was detected. The configuration of the monosaccharide unit in the crown ring influenced the absolute configuration of the epoxyketones synthesized.
-
Synthesis of chiral crown ethers derived from D-galactose and their application in enantioselective reactions
Tetrahedron, 2019Co-Authors: Zsolt Rapi, Tamás Nemcsok, György Keglevich, Péter Bagi, Péter BakóAbstract:Abstract A few new α- and β- d -galactopyranoside-based chiral lariat ethers of monoaza-15-crown-5 type were synthesized. These macrocycles proved to be efficient catalysts in a few asymmetric reactions under mild phase transfer conditions. The catalytic effect of the lariat ethers with methoxy, ethoxy, isopropoxy and aryloxy substituents on the C-1 of the sugar unit in both α and β positions was compared. In the presence of β- d -galactopyranoside-based crown ethers, the asymmetric Darzens Condensation of α-chloroacetophenone and benzaldehyde, the epoxidation of trans -chalcone, the cyclopropanation (MIRC reaction) of benzylidenemalononitrile and 2-benzylidene-1,3-indandione with diethyl bromomalonate were performed with enantioselectivities of 61%, 64%, 86% and 96%, respectively. In all reactions, the β-anomers were more efficient in terms of enantioselectivity than the α forms.
-
Synthesis of d-mannitol-based crown ethers and their application as catalyst in asymmetric phase transfer reactions.
Chirality, 2017Co-Authors: Tamás Nemcsok, Zsolt Rapi, György Keglevich, Alajos Grün, Péter BakóAbstract:: A few new d-mannitol-based monoaza-15-crown-5 type chiral lariat ethers and 18-crown-6 type macrocycles were synthesized. These crown compounds were used as phase transfer catalysts in asymmetric Michael addititons and in a Darzens Condensation under mild conditions to afford the corresponding products in a few cases in good to excellent enantioselectivities. In the Michael addition of diethyl acetoxymalonate to trans-chalcone, in the addition of diethyl acetamidomalonate to s-nitrostyrene, in the reaction of diethyl bromomalonate with benzylidene malononitriles, in the cyclopropanation reaction of diethyl bromomalonate and 2-benzylidene-1,3-indandione, and in the Darzens Condensation of α-chloroacetophenone with benzaldehyde, maximum enantioselectivities of 39%, 65%, 99%, 56%, and 62%, respectively, were obtained in the presence of the d-mannitol-based macrocycles as the catalysts.
-
Sugar-based Crown Ethers in Enantioselective Syntheses
Periodica Polytechnica Chemical Engineering, 2015Co-Authors: Péter Bakó, Zsolt Rapi, György KeglevichAbstract:A number of chiral macrocyclic compounds have been prepared that contain a monosaccharide-derived sub-unit. These sugar-based crown ethers were used as chiral phase transfer catalysts in a few asymmetric reactions. A few of them proved to be effective catalysts in Michael additions, a Darzens Condensation and an epoxidation of α,β-enones. It was found that the type of the monosaccharide, the substituents on the sugar unit and on the nitrogen atom of the macroring have a significant influence on both the yield and the enantioselectivity.
-
Side‐Arm Effect of a Methyl α‐d‐Glucopyranoside Based Lariat Ether Catalysts in Asymmetric Syntheses
Heteroatom Chemistry, 2014Co-Authors: Zsolt Rapi, Péter Bakó, László Drahos, György KeglevichAbstract:Methyl α-d-glucopyranoside based monoaza-15-crown-5 type lariat ethers with different heteroatom-containing side arm attached to the nitrogen of the macrocyclic ring have been synthesized. These compounds were used as chiral phase transfer catalysts in a few asymmetric reactions, such as Michael additions, Darzens Condensation, and epoxidation of chalcone. The side arms of the macrocycles had a significant impact on the chemical yields and the enantioselectivity. The effect of the lariat ethers with side arms having heteroatom (O, N, and S) was compared with the effect of the analogues having substituents without a heteroatom. The terminal allyl group also generated a significant enantioselectivity (79% enantiomeric excess) in one of the Michael additions. The application of crown ethers with substituents (CH2)3OH or (CH2)3OCH3 leads to the best enantioselectivities 85% and 99%, respectively.
John W Cran - One of the best experts on this subject based on the ideXlab platform.
-
the Darzens Condensation of α β unsaturated aldehydes and ketones
ChemInform, 2011Co-Authors: Marie E Krafft, Steven J R Twiddle, John W CranAbstract:Enolates of α-bromo esters (I) or ketones (V) undergo one-pot Darzens Condensation to give diastereomeric mixtures of epoxides.
-
The Darzens Condensation of α,β‐Unsaturated Aldehydes and Ketones.
ChemInform, 2011Co-Authors: Marie E Krafft, Steven J R Twiddle, John W CranAbstract:Enolates of α-bromo esters (I) or ketones (V) undergo one-pot Darzens Condensation to give diastereomeric mixtures of epoxides.
-
the Darzens Condensation of α β unsaturated aldehydes and ketones
Tetrahedron Letters, 2011Co-Authors: Marie E Krafft, Steven J R Twiddle, John W CranAbstract:The one-pot Darzens Condensation of α,β-unsaturated aldehydes and ketones with enolates of an α-bromo ester or ketone is described.
Zsolt Rapi - One of the best experts on this subject based on the ideXlab platform.
-
Synthesis of xylal- and arabinal-based crown ethers and their application as asymmetric phase transfer catalysts.
Chirality, 2019Co-Authors: Tamás Nemcsok, Zsolt Rapi, György Keglevich, Péter Bagi, Péter BakóAbstract:: New xylal- and arabinal-based monoaza-15-crown-5 ethers were synthesized starting from l- and d-xylose, and l- and d-arabinose, respectively. These monosaccharide-based chiral macrocycles were tested as phase transfer catalysts in a few asymmetric reactions. The xylal-based crown compounds proved to be efficient catalysts in a few liquid-liquid phase reactions. The epoxidation of trans-chalcone and the Darzens Condensation of α-chloroacetophenone with benzaldehyde took place with complete diastereoselectivity and up to 77% ee and 58% ee, respectively. It was found that the substituents in the aromatic ring of the chalcone and the α-chloroacetophenone had an influence on the enantioselectivity. The highest ee values were obtained in the epoxidation of 4-chlorochalcone (81% ee) and in the reaction of a 2-naphthyl analogue (96% ee), while in the Darzens Condensation of 4-phenyl-α-chloroacetophenone with benzaldehyde, a maximum ee of 91% was detected. The configuration of the monosaccharide unit in the crown ring influenced the absolute configuration of the epoxyketones synthesized.
-
Synthesis of chiral crown ethers derived from D-galactose and their application in enantioselective reactions
Tetrahedron, 2019Co-Authors: Zsolt Rapi, Tamás Nemcsok, György Keglevich, Péter Bagi, Péter BakóAbstract:Abstract A few new α- and β- d -galactopyranoside-based chiral lariat ethers of monoaza-15-crown-5 type were synthesized. These macrocycles proved to be efficient catalysts in a few asymmetric reactions under mild phase transfer conditions. The catalytic effect of the lariat ethers with methoxy, ethoxy, isopropoxy and aryloxy substituents on the C-1 of the sugar unit in both α and β positions was compared. In the presence of β- d -galactopyranoside-based crown ethers, the asymmetric Darzens Condensation of α-chloroacetophenone and benzaldehyde, the epoxidation of trans -chalcone, the cyclopropanation (MIRC reaction) of benzylidenemalononitrile and 2-benzylidene-1,3-indandione with diethyl bromomalonate were performed with enantioselectivities of 61%, 64%, 86% and 96%, respectively. In all reactions, the β-anomers were more efficient in terms of enantioselectivity than the α forms.
-
Synthesis of d-mannitol-based crown ethers and their application as catalyst in asymmetric phase transfer reactions.
Chirality, 2017Co-Authors: Tamás Nemcsok, Zsolt Rapi, György Keglevich, Alajos Grün, Péter BakóAbstract:: A few new d-mannitol-based monoaza-15-crown-5 type chiral lariat ethers and 18-crown-6 type macrocycles were synthesized. These crown compounds were used as phase transfer catalysts in asymmetric Michael addititons and in a Darzens Condensation under mild conditions to afford the corresponding products in a few cases in good to excellent enantioselectivities. In the Michael addition of diethyl acetoxymalonate to trans-chalcone, in the addition of diethyl acetamidomalonate to s-nitrostyrene, in the reaction of diethyl bromomalonate with benzylidene malononitriles, in the cyclopropanation reaction of diethyl bromomalonate and 2-benzylidene-1,3-indandione, and in the Darzens Condensation of α-chloroacetophenone with benzaldehyde, maximum enantioselectivities of 39%, 65%, 99%, 56%, and 62%, respectively, were obtained in the presence of the d-mannitol-based macrocycles as the catalysts.
-
Sugar-based Crown Ethers in Enantioselective Syntheses
Periodica Polytechnica Chemical Engineering, 2015Co-Authors: Péter Bakó, Zsolt Rapi, György KeglevichAbstract:A number of chiral macrocyclic compounds have been prepared that contain a monosaccharide-derived sub-unit. These sugar-based crown ethers were used as chiral phase transfer catalysts in a few asymmetric reactions. A few of them proved to be effective catalysts in Michael additions, a Darzens Condensation and an epoxidation of α,β-enones. It was found that the type of the monosaccharide, the substituents on the sugar unit and on the nitrogen atom of the macroring have a significant influence on both the yield and the enantioselectivity.
-
Side‐Arm Effect of a Methyl α‐d‐Glucopyranoside Based Lariat Ether Catalysts in Asymmetric Syntheses
Heteroatom Chemistry, 2014Co-Authors: Zsolt Rapi, Péter Bakó, László Drahos, György KeglevichAbstract:Methyl α-d-glucopyranoside based monoaza-15-crown-5 type lariat ethers with different heteroatom-containing side arm attached to the nitrogen of the macrocyclic ring have been synthesized. These compounds were used as chiral phase transfer catalysts in a few asymmetric reactions, such as Michael additions, Darzens Condensation, and epoxidation of chalcone. The side arms of the macrocycles had a significant impact on the chemical yields and the enantioselectivity. The effect of the lariat ethers with side arms having heteroatom (O, N, and S) was compared with the effect of the analogues having substituents without a heteroatom. The terminal allyl group also generated a significant enantioselectivity (79% enantiomeric excess) in one of the Michael additions. The application of crown ethers with substituents (CH2)3OH or (CH2)3OCH3 leads to the best enantioselectivities 85% and 99%, respectively.
Fabrice Gallou - One of the best experts on this subject based on the ideXlab platform.
-
development of a robust and practical process for the Darzens Condensation and α β epoxide rearrangement scope and limitations of the methodology
Synthesis, 2008Co-Authors: Jeremy Malcolm Zimbron, Manuela Seegerweibel, Hans Hirt, Fabrice GallouAbstract:A practical and robust process for the Darzens Condensation of substituted benzaldehydes and subsequent α,β-epoxy rearrangement is reported. The process developed is both amenable to large scale and parallel synthesis. While electron-poor benzaldehydes gave mixtures of aryl ketones and 2-substituted aryl ketones in mediocre to low yields, electron-rich benzaldehydes were found to react in high yields with complete regioselectivity to form 2-substituted aryl ketones.
-
Development of a Practical Route for the Manufacture of N-[5-(3-Imidazol-1-yl-4-methanesulfonyl-phenyl)-4-methyl-thiazol-2-yl]acetamide
Organic Process Research & Development, 2008Co-Authors: Hans Hirt, Ruedi Haenggi, Jesus Reyes, Manuela Seeger-weibel, Fabrice GallouAbstract:An efficient synthesis of a potent candidate in our respiratory program is described. The synthesis based on a key Darzens Condensation−α,β-epoxide rearrangement circumvented the toxicity and safety issues encountered in the original synthesis route. Subsequent functionalization and formation of an heterocyclic moiety is presented with a particular emphasis on the practicality, robustness, and streamlining of the process.
