The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Xumu Zhang - One of the best experts on this subject based on the ideXlab platform.
-
Developing chiral phosphorus ligands for asymmetric hydrogenations
Pure and Applied Chemistry, 2010Co-Authors: Guohua Hou, Weicheng Zhang, Xianfeng Sun, Gao Shang, Xumu ZhangAbstract:Chiral rigid and electron-donating phosphocyclic phosphine ligands and modular atropisomeric biaryl phosphine ligands were designed and synthesized. The performance of these chiral ligands in the asymmetric hydrogenations of prochiral Dehydroamino Acid deriv- atives, enamides, imines, keto esters, and ketones has been demonstrated to be excellent.
-
enantioselective hydrogenation of α Dehydroamino Acid esters catalyzed by rhodium complexes with chiral bisaminophosphine ligands
Advanced Synthesis & Catalysis, 2010Co-Authors: Xianfeng Sun, Le Zhou, Xumu ZhangAbstract:A highly efficient strategy for the synthesis of a series of chiral bisaminophosphine ligands was well established with several remarkable features. The synthetic utility of these ligands was explored for rhodium-catalyzed asymmetric hydrogenations of α-Dehydroamino Acid esters. Up to 98% ee values were achieved for the enantioselective synthesis of aminocarboxylic Acids and their derivatives, which are very important chiral building blocks for the synthesis of a variety of natural products and biologically active molecules.
-
Enantioselective Hydrogenation of α‐Dehydroamino Acid Esters Catalyzed by Rhodium Complexes with Chiral Bisaminophosphine Ligands
Advanced Synthesis & Catalysis, 2010Co-Authors: Xianfeng Sun, Le Zhou, Xumu ZhangAbstract:A highly efficient strategy for the synthesis of a series of chiral bisaminophosphine ligands was well established with several remarkable features. The synthetic utility of these ligands was explored for rhodium-catalyzed asymmetric hydrogenations of α-Dehydroamino Acid esters. Up to 98% ee values were achieved for the enantioselective synthesis of aminocarboxylic Acids and their derivatives, which are very important chiral building blocks for the synthesis of a variety of natural products and biologically active molecules.
-
A convenient synthesis and the asymmetric hydrogenation of N-phthaloyl Dehydroamino Acid esters.
Organic letters, 2008Co-Authors: Jian Chen, Qiang Liu, Weicheng Zhang, Stephen Spinella, Aiwen Lei, Xumu ZhangAbstract:A convenient synthetic method was reported for the preparation of N-phthaloyl Dehydroamino Acid esters from easily accessible vinyl bromides (or vinyl tosylate) and potassium phthalimide. Rh-catalyzed asymmetric hydrogenation of these substrates with TangPhos gave the products with good to excellent enantioselectivities (up to 99% ee).
Tsuneo Imamoto - One of the best experts on this subject based on the ideXlab platform.
-
Three-Hindered Quadrant Phosphine Ligands with an Aromatic Ring Backbone for the Rhodium-Catalyzed Asymmetric Hydrogenation of Functionalized Alkenes
2016Co-Authors: Zhenfeng Zhang, Ken Tamura, Daisuke Mayama, Masashi Sugiya, Tsuneo ImamotoAbstract:The three-hindered quadrant phosphine ligands (R)-1-tert-butylmethylphosphino-2-(di-tert-butylphosphino)benzene ((R)-3H-BenzP*) and (R)-2-tert-butylmethylphosphino-3-(di-tert-butylphosphino)quinoxaline ((R)-3H-QuinoxP*) exhibited good to excellent enantioselectivities in the rhodium-catalyzed asymmetric hydrogenation of selected Dehydroamino Acid derivatives, enamides, and ethenephosphonates
-
three hindered quadrant phosphine ligands with an aromatic ring backbone for the rhodium catalyzed asymmetric hydrogenation of functionalized alkenes
ChemInform, 2012Co-Authors: Zhenfeng Zhang, Ken Tamura, Daisuke Mayama, Masashi Sugiya, Tsuneo ImamotoAbstract:The Rh catalysts (I) and (II) (0.1-0.5 mol%) are highly efficient in the asymmetric hydrogenation (3-10 atm H2) of various Dehydroamino Acid derivatives and ethenephosphonates (XV).
-
three hindered quadrant phosphine ligands with an aromatic ring backbone for the rhodium catalyzed asymmetric hydrogenation of functionalized alkenes
Journal of Organic Chemistry, 2012Co-Authors: Zhenfeng Zhang, Ken Tamura, Daisuke Mayama, Masashi Sugiya, Tsuneo ImamotoAbstract:The three-hindered quadrant phosphine ligands (R)-1-tert-butylmethylphosphino-2-(di-tert-butylphosphino)benzene ((R)-3H-BenzP*) and (R)-2-tert-butylmethylphosphino-3-(di-tert-butylphosphino)quinoxaline ((R)-3H-QuinoxP*) exhibited good to excellent enantioselectivities in the rhodium-catalyzed asymmetric hydrogenation of selected Dehydroamino Acid derivatives, enamides, and ethenephosphonates.
-
Highly Enantioselective Hydrogenation of α-Dehydroamino Acids by Rhodium Complexes with New Unsymmetric P−Chirogenic Bisphosphine Ligands
Organic letters, 2001Co-Authors: Atsushi Ohashi And, Tsuneo ImamotoAbstract:New rhodium catalysts with unsymmetric P−chirogenic bis(phosphino)ethanes, BisP*−Rh, exhibited very high enantioselectivity (98−99%) in the hydrogenation of α-Dehydroamino Acid derivatives. Such high enantioselectivity should result from the asymmetric environment around the Rh atom, as was shown in the molecular structure of the catalyst analyzed by X-rays. The asymmetry can be controlled by the combination of the alkyl groups on the two phosphorus atoms.
Albert S. C. Chan - One of the best experts on this subject based on the ideXlab platform.
-
The synthesis of new chiral phosphine-phosphinites, phosphine-phosphoramidite, and phosphine-phosphite ligands and their applications in asymmetric hydrogenation
Tetrahedron: Asymmetry, 2004Co-Authors: Xian Jia, Chi-hung Yeung, Sze Lam, Stanton Hon Lung Kok, Albert S. C. ChanAbstract:Abstract New chiral phosphine-phosphinite, phosphine–phosphoramidite ligands and phosphine–phosphite 1a , 1b , 2 and 3 have been synthesized and examined in the enantioselective hydrogenation of Dehydroamino Acid derivatives and α-aryl enamides. The results demonstrate that both rhodium- 1b and rhodium- 2 complexes were highly efficient catalysts in asymmetric hydrogenation reactions (up to 99.6% ee was obtained).
-
Highly Efficient Rhodium/Monodentate Phosphoramidite Catalyst and Its Application in the Enantioselective Hydrogenation of Enamides and α-Dehydroamino Acid Derivatives
The Journal of organic chemistry, 2003Co-Authors: Xian Jia, Qian Shi, Xin-sheng Yao, Albert S. C. ChanAbstract:An easily prepared and highly efficient monodentate phosphoramidite ligand derived from BINOL, (S)-2,2‘-O,O-(1,1‘-binaphthyl)-dioxo-N,N-diethylphospholidine, was examined in the hydrogenation of both enamides and α-Dehydroamino Acid derivatives. The catalyst provided remarkably high enantioselectivities (up to 99.6% ee for enamides and >99.9% ee for α-Dehydroamino Acid derivatives).
-
highly efficient rhodium monodentate phosphoramidite catalyst and its application in the enantioselective hydrogenation of enamides and α Dehydroamino Acid derivatives
Journal of Organic Chemistry, 2003Co-Authors: Xian Jia, Qian Shi, Xin-sheng Yao, Albert S. C. ChanAbstract:An easily prepared and highly efficient monodentate phosphoramidite ligand derived from BINOL, (S)-2,2‘-O,O-(1,1‘-binaphthyl)-dioxo-N,N-diethylphospholidine, was examined in the hydrogenation of both enamides and α-Dehydroamino Acid derivatives. The catalyst provided remarkably high enantioselectivities (up to 99.6% ee for enamides and >99.9% ee for α-Dehydroamino Acid derivatives).
-
Aminophosphine Phosphinites Derived from Chiral 1,2-Diphenyl-2-aminoethanols: Synthesis and Application in Rhodium-Catalyzed Asymmetric Hydrogenation of Dehydroamino Acid Derivatives
Tetrahedron, 2000Co-Authors: Rongliang Lou, Yaozhong Jiang, Yong Qin, Albert S. C. ChanAbstract:Abstract A series of chiral aminophosphine phosphinites DPAMPPs was synthesized from optically active 1,2-diphenyl-2-aminoethanols. The erythro-DPAMPPs were found to serve as excellent ligands for rhodium-catalyzed asymmetric hydrogenation of Dehydroamino Acid derivatives. For an array of Dehydroamino Acid precursors, remarkably high enantioselectivity (up to 98.4% e.e.) and reactivity (the ratio of substrate/catalyst up to 10000) were observed. Some factors controlling the enantioselectivity were examined and discussed.
-
Asymmetric hydrogenation of Dehydroamino Acid derivatives catalyzed by a new aminophosphine phosphinite ligand derived from ketopinic Acid
Tetrahedron: Asymmetry, 2000Co-Authors: Rongliang Lou, Albert S. C. Chan, Chi-hung Yeung, Wai-kwok WongAbstract:Abstract A new chiral aminophosphine phosphinite N , O -bis(diphenylphosphino)-(1 S ,2 R )-1-( N -methylamino) methyl-2-hydroxyl-7,7-dimethylbicyclo[2.2.1]heptane was synthesized from ketopinic Acid and its application to the asymmetric hydrogenation of Dehydroamino Acid derivatives examined.
Luís S. Monteiro - One of the best experts on this subject based on the ideXlab platform.
-
Synthesis and preliminary biological evaluation of new phenolic and catecholic Dehydroamino Acid derivatives
Tetrahedron, 2017Co-Authors: Luís S. Monteiro, Paula M. T. Ferreira, Sandra Oliveira, Fátima Paiva-martins, David M. Pereira, Paula B. Andrade, Patrícia ValentãoAbstract:Abstract A library of N -phenolic and N -catecholic Dehydroamino Acid derivatives was prepared using an innovative synthetic strategy that involves mild reaction conditions and simple work-up procedures. The method comprises coupling of phenolic or catecholic Acids with β-hydroxyamino Acids followed by tert -butyloxycarbonylation of all hydroxyl groups using tert -butyldicarbonate and 4-dimethylaminopyridine as catalyst. Treatment of these amino Acids with N,N,N′,N′ -tetramethylguanidine affords the corresponding O - tert -butyloxycarbonylDehydroamino Acid derivative. Deprotection of the aromatic hydroxyl groups is carried out with trifluoroacetic Acid. This synthetic strategy can be applied in a one-pot procedure and yields compounds that can be easily inserted into peptides or other biomolecules after cleavage of the C-protecting group. Preliminary studies of cell viability show that these new compounds display very low or no toxicity. These Dehydroamino Acids with a phenolic or catecholic moiety can have intrinsic biological activity or used to prepare new hydrogels that mimic mussel adhesive proteins.
-
High yielding synthesis of N-ethyl Dehydroamino Acids
Amino Acids, 2012Co-Authors: Luís S. Monteiro, Ana S. SuárezAbstract:Recently we reported the use of a sequence of alkylation and dehydration methodologies to obtain N -ethyl-α, β-Dehydroamino Acid derivatives. The application of this N-alkylation procedure to several methyl esters of β,β-dibromo and β-bromo, β-substituted Dehydroamino Acids protected with standard amine protecting groups was subsequently reported. The corresponding N -ethyl, β-bromo Dehydroamino Acid derivatives were obtained in fair to high yields and some were used as substrates in Suzuki cross-coupling reactions to give N -ethyl, β,β-disubstituted dehydroalanine derivatives. Herein, we further explore N-ethylation of β-halo Dehydroamino Acid derivatives using triethyloxonium tetrafluoroborate as alkylating agent, but substituting N,N -diisopropylethylamine for potassium tert -butoxide as auxiliary base. In these conditions, for all β-halo Dehydroamino Acid derivatives, reactions were complete and the N -ethylated derivative could be isolated in high yield. This method was also applied for N-ethylation of non-halogenated Dehydroamino Acids. Again, with all compounds the reactions were complete and the N -ethyl Dehydroamino Acid derivatives could be isolated in high yields. Some of these N -ethyl Dehydroamino Acid methyl ester derivatives were converted in high yields to their corresponding Acids and coupled to an amino Acid methyl ester to give N -ethyl dehydrodipeptide derivatives in good yields. Thus, this method constitutes a general procedure for high yielding synthesis of N -ethylated Dehydroamino Acids, which can be further applied in peptide synthesis.
-
Synthesis of Novel Nonproteinogenic Amino Acids: N-Ethyl-α,β-Dehydroamino Acid Methyl Esters
European Journal of Organic Chemistry, 2010Co-Authors: Luís S. Monteiro, Joanna Kołomańska, Ana C. SuárezAbstract:Two routes for the synthesis of N-ethyl-N-(4-nitrophenyl-sulfonyl)-α,β-Dehydroamino Acid derivatives from serine, threonine and phenylserine derivatives are presented. One route consists of dehydration of N-(4-nitrophenylsulfonyl)-β-hydroxyamino Acid esters with di-tert-butyl dicarbonate catalyzed by 4-(dimethylamino)pyridine, followed by alkylation of the N-(4-nitrophenylsulfonyl)-α,β-Dehydroamino Acid methyl esters obtained with triethyloxonium tetrafluoroborate. The second strategy applied the same procedures but in inverse order: alkylation followed by dehydration. These methods made it possible to obtain for the first time, new non-natural amino Acids, which incorporate both an N-ethyl and an α,β-dehydro moiety.
-
synthesis of non proteinogenic amino Acids from n 4 toluenesulfonyl Dehydroamino Acid derivatives
Tetrahedron Letters, 2002Co-Authors: Paula M. T. Ferreira, Hernâni L. S. Maia, Luís S. MonteiroAbstract:By treating N-(4-toluenesulfonyl)-N-(tert-butyloxycarbonyl)-Dehydroamino Acid derivatives with different reactants under different conditions, a variety of new amino Acids are obtained, viz. (i) α-alcoxy-α-amino Acids, (ii) α,α-diamino Acids and (iii) novel β-substituted Dehydroamino Acids.
-
michael addition of thiols carbon nucleophiles and amines to Dehydroamino Acid and dehydropeptide derivatives
Journal of The Chemical Society-perkin Transactions 1, 2001Co-Authors: Paula M. T. Ferreira, Luís S. Monteiro, Hernâni L. S. Maia, Joana SacramentoAbstract:Michael additions of nitrogen heterocycles, thiols, carbon nucleophiles and amines to dehydroalanine derivatives, including a glycyldehydroalanine peptide, are performed in fair to good yields. DiDehydroaminobutyric Acid derivatives react only with the stronger nucleophiles but in considerably lower yields and often no reaction is observed with the corresponding didehydrophenylalanine derivatives. When a tosyl group is bonded to the nitrogen atom of the Dehydroamino Acid, in some cases the addition product undergoes elimination of this group and yields the corresponding β-substituted derivative of the α,β-diDehydroamino Acid. Addition of some β-dicarbonyl compounds leads to formation of products to which the structure of α,α-disubstituted cyclic amino Acid derivatives is assigned.
Matthias Beller - One of the best experts on this subject based on the ideXlab platform.
-
iridium catalyzed hydrogenation of β Dehydroamino Acid derivatives using monodentate phosphoramidites
European Journal of Organic Chemistry, 2008Co-Authors: Stephan Enthaler, Giulia Erre, Kathrin Junge, Kristin Schröder, Daniele Addis, Dirk Michalik, Marko Hapke, Dmitry Redkin, Matthias BellerAbstract:The iridium-catalyzed asymmetric hydrogenation of 13 different β-Dehydroamino Acid derivatives to give optically active β-amino Acid esters has been examined. Readily accessible monodentate octahydrobinaphthol-based phosphoramidites were used as chiral ligands. Good to excellent enantioselectivities and yields were obtained for the E isomers, whereas poorer catalyst performance was found for the Z isomers. Importantly, to obtain high enantioselectivity, substitution at the 3,3′-positions of the ligands was necessary. Enantioselectivities of up to 94 % ee were achieved under optimized conditions.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
-
Iridium‐Catalyzed Hydrogenation of β‐Dehydroamino Acid Derivatives Using Monodentate Phosphoramidites
European Journal of Organic Chemistry, 2008Co-Authors: Stephan Enthaler, Giulia Erre, Kathrin Junge, Kristin Schröder, Daniele Addis, Dirk Michalik, Marko Hapke, Dmitry Redkin, Matthias BellerAbstract:The iridium-catalyzed asymmetric hydrogenation of 13 different β-Dehydroamino Acid derivatives to give optically active β-amino Acid esters has been examined. Readily accessible monodentate octahydrobinaphthol-based phosphoramidites were used as chiral ligands. Good to excellent enantioselectivities and yields were obtained for the E isomers, whereas poorer catalyst performance was found for the Z isomers. Importantly, to obtain high enantioselectivity, substitution at the 3,3′-positions of the ligands was necessary. Enantioselectivities of up to 94 % ee were achieved under optimized conditions.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
-
Development of Practical Rhodium Phosphine Catalysts for the Hydrogenation of β-Dehydroamino Acid Derivatives
Organic Process Research & Development, 2007Co-Authors: Stephan Enthaler, Giulia Erre, Kathrin Junge, Jens Holz, Armin Börner, Elisabetta Alberico, Ilenia Nieddu, Serafino Gladiali, Matthias BellerAbstract:The rhodium-catalyzed asymmetric hydrogenation of various β-Dehydroamino Acid derivatives to give optically active β-amino Acids has been examined. Chiral monodentate 4,5-dihydro-3H-dinaphthophosphepines, which are easily tuned and accessible in a multi-10-g scale, have been used as ligands. The enantioselectivity is largely dependent on the nature of the substituent at the phosphorous atom and on the structure of the substrate. Applying optimized conditions up to 94% ee was achieved.