- Asymmetric hydroformylation of N-acyl 1-aminoacrylic acid derivatives by rhodium/chiral diphosphine catalysts
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The asymmetric hydroformylation of N-acylaminoacrylic acid esters 1 is efficiently catalysed by HRh(CO)(PPh3)3 in the presence of DIOP and related diphosphines as chiral ligands. The reaction is completely regioselective and affords
- Gladiali,Pinna
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Read Online
- Concise synthesis and applications of enantiopure spirobiphenoxasilin-diol and its related chiral ligands
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The development of chiral architectures for chiral ligand and catalyst discovery is essential for asymmetric catalysis. Herein, we report the concise synthesis of a Si-centered spirocyclic skeleton, spirobiphenoxasilin-diol (SPOSiOL), and its derived chiral ligands. Using the chemical resolution method, the optical SPOSiOL could be obtained in high yield on a gram scale. Preliminary studies indicated that this ligand scaffold has great potential in transition metal-catalyzed asymmetric reactions. This finding further highlights that the Si-centered spirocyclic scaffolds are of great value in asymmetric catalysis. This journal is
- Liu, Tao,Wang, Biqin,Wang, Peng,Wu, Yichen,Xu, Wen-Qiang,Yang, Lei
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p. 13365 - 13368
(2021/12/17)
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- Nickel-Catalyzed Asymmetric Hydrogenation of 2-Amidoacrylates
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Earth-abundant nickel, coordinated with a suitable chiral bisphosphine ligand, was found to be an efficient catalyst for the asymmetric hydrogenation of 2-amidoacrylates, affording the chiral α-amino acid esters in quantitative yields and excellent enantioselectivity (up to 96 % ee). The active catalyst component was studied by NMR and HRMS, which helped us to realize high catalytic efficiency on a gram scale with a low catalyst loading (S/C=2000). The hydrogenated products could be simply converted into chiral α-amino acids, β-amino alcohols, and their bioactive derivatives. Furthermore, the catalytic mechanism was investigated using deuterium-labeling experiments and computational calculations.
- Chen, Jianzhong,Gridnev, Ilya D.,Hu, Yawen,Li, Bowen,Zhang, Wanbin,Zhang, Zhenfeng
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supporting information
p. 5371 - 5375
(2020/02/15)
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- Topology-Based Functionalization of Robust Chiral Zr-Based Metal-Organic Frameworks for Catalytic Enantioselective Hydrogenation
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The design and development of robust and porous supported catalysts with high activity and selectivity is extremely significant but very challenging for eco-friendly synthesis of fine chemicals and pharmaceuticals. We report here the design and synthesis of highly stable chiral Zr(IV)-based MOFs with different topologies to support Ir complexes and demonstrate their network structures-dependent asymmetric catalytic performance. Guided by the modulated synthesis and isoreticular expansion strategy, five chiral Zr-MOFs with a flu or ith topology are constructed from enantiopure 1,1′-biphenol-derived tetracarboxylate linkers and Zr6, Zr9, or Zr12 clusters. The obtained MOFs all show high chemical stability in boiling water, strongly acidic, and weakly basic aqueous solutions. The two flu MOFs featuring the dihydroxyl groups of biphenol in open and large cages, after sequential postsynthetic modification with P(NMe2)3 and [Ir(COD)Cl]2, can be highly efficient and recyclable heterogeneous catalysts for hydrogenation of α-dehydroamino acid esters with up to 98% ee, whereas the three ith MOFs featuring the dihydroxyl groups in small cages cannot be installed with P(NMe2)3 to support the Ir complex. Incorporation of Ir-phosphorus catalysts into Zr-MOFs leads to great enhancement of their chemical stability, durability, and even stereoselectivity. This work therefore not only advances Zr-MOFs as stable supports for labile metal catalysts for heterogeneous asymmetric catalysis but also provides a new insight into how highly active chiral centers can result due to the framework topology.
- Jiang, Hong,Zhang, Wenqiang,Kang, Xing,Cao, Ziping,Chen, Xu,Liu, Yan,Cui, Yong
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supporting information
p. 9642 - 9652
(2020/07/02)
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- Silver-Promoted Direct Phosphorylation of Bulky C(sp2)-H Bond to Build Fully Substituted β-Phosphonodehydroamino Acids
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A general and practical cross-dehydrogenative coupling protocol between readily available trisubstituted α,β-dehydro α-amino carboxylic esters and H-phosphites is described. This C(sp2)-H phosphorylation reaction proceeds with absolute Z-selectivity promoted by silver salt in a radical relay manner. The bulky tetrasubstituted β-phosphonodehydroamino acids were obtained in grams and added new modules to the toolkit for peptide modifications.
- Cao, Hao-Qiang,Liu, Hao-Nan,Liu, Zhe-Yuan,Qiao, Baokun,Zhang, Fa-Guang,Ma, Jun-An
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supporting information
p. 6414 - 6419
(2020/09/02)
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- Ni(ii)-Catalyzed vinylic C-H functionalization of 2-acetamido-3-arylacrylates to access isotetronic acids
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A ligand-free Ni(ii)-catalyzed cascade annulation reaction for the synthesis of 4-aryl-substituted isotetronic acids from 2-acetamido-3-arylacrylatesviavinylic C-H functionalization is reported. The reaction proceeds through heteroatom guided electrophilic insertion of nickel to the vinylic double bond followed by annulation with dibromomethane. This unconventional route features cascade steps, sole product formation, multiple functional group tolerance, low cost of catalysts and reagents, and readily available starting materials. Using this method, various aryl-substituted isotetronic acids have been synthesized which are biologically relevant. The annulation of 2-acetamido-3-arylacrylates has also been assessed with 1,2-dichloroethane, which resulted in the rearranged annulated products of 5-methyl substituted isotetronic acids.
- Das, Eshani,Mal, Dipakranjan,Roy, Avijit,Roy, Biswajit
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supporting information
p. 3697 - 3706
(2020/06/03)
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- Hypervalent iodane mediated reactions of: N -acetyl enamines for the synthesis of oxazoles and imidazoles
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A hypervalent iodane reagent used for the intramolecular cyclization of N-acetyl enamines and intermolecular cyclocondensation of enamines and nitriles was investigated. The reaction was performed under mild conditions and gave oxazoles and imidazoles, respectively, in moderate to excellent yields. This transformation exhibits good reactivity, selectivity and functional group tolerance. The selectivity of the intra- or intermolecular reaction is dependent on the structure of N-acetyl enamines.
- Xu, Kang,Yang, Ruiqi,Yang, Shuang,Jiang, Cheng,Ding, Zhenhua
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supporting information
p. 8977 - 8981
(2019/10/28)
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- Novel biferrocene-based phosphoramidite ligands: The combination of a rather unexplored chiral backbone and a privileged ligand scaffold
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A small library of novel chiral monodentate phosphoramidite ligands, characterized by a dihydroazepine-biferrocene backbone was prepared. In order to obtain this biferrocene substructure, a mild and efficient homocoupling was developed. This allowed to synthesize the dihydroazepine ligand precursor and the phosphoramidite ligands with good overall yields and high enantiomeric excess. These ligands were successfully tested in a rhodium(I)-catalyzed hydrogenation of activated olefins.
- Kimpe,Janssens,Bert,Wackens,Goeman,Van der Eycken
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supporting information
(2019/10/16)
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- An Atropos Chiral Biphenyl Bisphosphine Ligand Bearing Only 2,2′-Substituents and Its Application in Rh-Catalyzed Asymmetric Hydrogenation
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An atropos chiral biphenyl bisphosphine ligand bearing only 2,2′-substituents was rationally designed and easily synthesized utilizing a bulky chiral t-butylmethylphosphino block. Computational results showed a large difference in the free energies betwee
- Jia, Jia,Ling, Zheng,Zhang, Zhenfeng,Tamura, Ken,Gridnev, Ilya D.,Imamoto, Tsuneo,Zhang, Wanbin
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p. 738 - 743
(2017/12/26)
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- Temperature-controlled bidirectional enantioselectivity in a dynamic catalyst for asymmetric hydrogenation
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Asymmetric catalysis using enantiomerically pure catalysts is one of the most widely used methods for the preparation of enantiomerically pure compounds. The separate synthesis of both enantiomerically pure compounds requires tedious and time-consuming pr
- Storch, Golo,Trapp, Oliver
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supporting information
p. 3580 - 3586
(2015/03/18)
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- Cation-triggered switchable asymmetric catalysis with chiral aza-crownphos
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An aza-crown ether, modified phosphoramidite ligand, has been designed and synthesized. The ON/OFF reversible switch of catalytic activity for its rhodium catalyst was thoroughly investigated in the asymmetric hydrogenation of dehydroamino acid esters modulated by host-guest interactions. In the OFF state, the catalyst is almost inactive (less than 1% conversion) because of the formation of an intermolecular sandwich complex by two aza-crown ether moities and the cationic rhodium metal center. In using alkali-metal-cations as the trigger, the catalytic activity was turned ON and consequently resulted in full conversions and excellent enantioselectivities (up to 98% ee).
- Ouyang, Guang-Hui,He, Yan-Mei,Li, Yong,Xiang, Jun-Feng,Fan, Qing-Hua
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supporting information
p. 4334 - 4337
(2015/04/14)
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- Cyclic decapeptide gramicidin S derivatives containing phosphines: Novel ligands for asymmetric catalysis
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The cyclic peptide gramicidin S was used as a rigid template to provide novel peptide-based bisphosphine ligands for transition metal catalysis. Two bisphosphine-coordinated Rh(i) complexes allowed asymmetric hydrogenation with 10-52% ee and the corresponding Pd(ii) analogues catalysed asymmetric allylic alkylation with 13-15% ee. The Royal Society of Chemistry 2013.
- Guisado-Barrios, Gregorio,Mu?oz, Bianca K.,Kamer, Paul C. J.,Lastdrager, Bas,Van Der Marel, Gijs,Overhand, Mark,Vega-Vázquez, Marino,Martin-Pastor, Manuel
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supporting information
p. 1973 - 1978
(2013/05/22)
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- Stereoselective Synthesis of (E)-α,β-dehydroamino acid esters
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Dehydroamino acid (Dhaa) is recognized as a useful tool or substrate for amino acid and peptide research. Although the stereoselective synthesis of the thermodynamically more stable Z-Dhaa has been well examined and established, the stereoselective synthesis of E-Dhaa has still remained to be a challenging synthetic task. In this paper, a stereoselective synthesis of E-Dhaa esters using a new (α-diphenylphosphono)glycine is described. The characteristic aspects of the new method are summarized as follows: (i) metal additives play an important role in the promotion of E-stereoselectivities. (ii) the use of NaI was effected for the synthesis of E-Dhaas bearing an aryl substituent and an amino functionality, (iii) MgBr2·OEt2 and ZnCl 2 contributed to improve the E-stereoselective synthesis of E-Dhaas bearing an alkyl substituent and an oxygen functionality, (iv) various protecting and functional groups were compatible under the reaction conditions, and (v) N-Cbz, Boc, and acyl-α-(diphenylphosphono)glycines were served for the stereoselective olefination reaction to provide the corresponding E-Dhaas. A variety of (E)-dehydroamino acid esters were stereoselectively synthesized by using (diphenylphosphono)glycinate. The stereoselectivity was influenced by metal additives. Various (E)-dehydroamino acid esters were prepared by the condensation reaction of the new phosphonates with easily available aldehydes by choosing the appropriate reaction conditions.
- Yasuno, Yoko,Hamada, Makoto,Yamada, Takeshi,Shinada, Tetsuro,Ohfune, Yasufumi
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supporting information
p. 1884 - 1888
(2013/05/08)
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- Asymmetric hydrogenation using rhodium complexes generated from mixtures of monodentate neutral and anionic phosphorus ligands
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A series of monodentate neutral and anionic phosphorus ligands was synthesized and evaluated in the asymmetric rhodium-catalyzed hydrogenation of functionalized olefins by using either catalysts containing identical ligands or catalysts generated from mixtures of two different ligands. We expected that the combination of an anionic ligand with a neutral ligand would favor the formation of hetero over homo bis-ligand complexes due to charge repulsion. NMR spectroscopic studies confirmed that charge effects can indeed shift the equilibrium toward the hetero bis-ligand complexes. In several cases, the combination of a neutral phosphane with an anionic phosphane, one chiral and the other achiral, furnished significantly higher enantioselectivities than analogous mixtures of two neutral ligands. The best results were obtained with a mixture of an anionic phosphoramidite and a neutral phosphoric acid diester. It is supposed that in this case a hydrogen bond between the two ligands additionally stabilizes the hetero ligand combination. Charge effects and hydrogen bonding favor the formation of rhodium hetero bis-ligand complexes from mixtures of neutral and anionic monodentate phosphorus ligands. The combination of a neutral phosphoric acid diester as a hydrogen donor and an anionic phosphoramidite as a hydrogen acceptor gives very high enantioselectivities in Rh-catalyzed hydrogenation reactions, thus exceeding the ee values of the corresponding homo bis-ligand complexes (see scheme). Copyright
- Frank, Dominik J.,Franzke, Axel,Pfaltz, Andreas
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supporting information
p. 2405 - 2415
(2013/03/28)
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- Synthesis of oxazoles from enamides via phenyliodine diacetate-mediated intramolecular oxidative cyclization
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A group of functionalized oxazoles were synthesized in moderate to good yields from enamides via phenyliodine diacetate (PIDA)-mediated intramolecular cyclization. The main advantageous features of the present method include its broad substrate scope and the heavy-metal-free characteristic of the oxidative carbon-oxygen bond formation process.
- Zheng, Yunhui,Li, Xuming,Ren, Chengfeng,Zhang-Negrerie, Daisy,Du, Yunfei,Zhao, Kang
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p. 10353 - 10361
(2013/01/15)
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- Practical preparation of Z-α-(N-acetylamino)- and Z-α-(N-benzoylamino)-α,β-unsaturated acids
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An efficient two-step synthetic procedure for the preparation of numerous variations of N-protected α,β-unsaturated α-amino acids and their corresponding esters from N-protected glycine and either aliphatic or aromatic aldehydes was developed. The reaction involved cyclization of the N-protected glycine into oxazolone, condensation with the aldehyde, and ring opening with a base. Copyright Taylor & Francis Group, LLC.
- Jursic, Branko S.,Sagiraju, Sarada,Ancalade, Dustin K.,Clark, Traneil,Stevens, Edwin D.
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p. 1709 - 1714
(2008/02/01)
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- Exploiting noninnocent (E,E)-dibenzylideneacetone (dba) effects in palladium(0)-mediated cross-coupling reactions: Modulation of the electronic properties of dba affects catalyst activity and stability in ligand and ligand-free reaction systems
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The reactivity of palladium(0) complexes, [Pd2 0(dba-n,n′-Z)3] (n,n′-Z = 4,4′-F; 4,4′-CF3; 4,4′-H; 4,4′-MeO) and [Pd 0(dba-n,n′-Z)2] (n,n′-Z = 4,4′-CF 3; 4,4′-H; 3,3′,5,5′-OMe),
- Fairlamb, Ian J. S.,Kapdi, Anant R.,Lee, Adam F.,McGlacken, Gerard P.,Weissburger, Felix,De Vries, Andre H. M.,Schmieder-Van De Vondervoort, Lizette
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p. 8750 - 8761
(2007/10/03)
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- Rhodium complexes with chiral counterions: Achiral catalysts in chiral matrices
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The neutral complexes [Rh(I)(NBD)((1S)-10-camphorsulfonate)] (2) and [Rh(I)((R)-N-acetylphenylalanate)] (4) reacted with bis-(diphenylphosphino)ethane (dppe) to form the cationic Rh(I)(NBD)(dppe) complexes, 5 and 6, respectively, accompanied by their corresponding chiral counteranions. Analogously, 4 reacted with 4,4′-dimethylbipyridine to yield complex 7. Complexes 5 and 6 disproportionated in aprotic solvents to form the corresponding bis-diphosphine complexes 8 and 9, respectively. 8 was characterized by an X-ray crystal structure analysis. In order to form achiral Rh(I) complexes bearing chiral countercations new sulfonated monophosphines 13-16 with chiral ammonium cations were synthesized. Tris-triphenylphosphinosulfonic acid (H3TPPS, 11) was used to protonate chiral amines to yield chiral ammonium phosphines 14-16. Thallium-tris-triphenylphosphinosulfonate (Tl3TPPS, 12) underwent metathesis with a chiral quartenary ammonium iodide to yield the proton free chiral ammonium phosphine 13. Phosphines 15 and 16 reacted with [Rh(NBD)2]BF4 to afford the highly charged chiral zwitterionic complexes [Rh(NBD) (TPPS)2][(R)-N, N-dimethyl-1-(naphtyl)ethylammonium] 5 (17) and [Rh(NBD)(TPPS)2][BF4] [(R)-N, N-dimethyl-phenethylammonium]6 (18), respectively. Complexes 5, 6, and 18 were tested as precatalysts for the hydrogenation of de-hydro-N-acetylphenylalanine (19) and methyl-(Z)-(α) -acetoamidocinnamate (MAC, 20) under homogeneous and heterogeneous (silica-supported and self-supported) conditions. None of the reactions was enantioselective.
- Dorta, Romano,Shimon, Linda,Milstein, David
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p. 751 - 758
(2007/10/03)
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- Synthesis and catalytic activities of PdII-phosphine complexes modified poly(ether imine) dendrimers
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In this paper, we report synthesis of new alkyldiphenyl phosphine ligand modified poly(ether imine) dendrimers up to the third generation. The phosphinated dendrimers were obtained by functional group transformations of the alcohols present at the periphery of the dendrimers to chloride, followed by phosphination using LiPPh2. The modification at the peripheries of the dendrimers was performed successfully to obtain up to 16 alkyl diphenylphosphines in the case of a third generation dendrimer, in good yields for each individual step. After phosphination, dendritic ligands were complexed with Pd(COD)Cl2 to give dendritic phosphine-PdII complexes. Both the ligands and the metal complexes were characterized by spectroscopic and spectrometric techniques including high-resolution mass spectral analysis for the lower generations. Evaluation of the catalytic efficacies of the dendrimer-PdII metal complexes in mediating a prototypical C-C bond forming reaction, namely the Heck reaction, was performed using various olefin substrates. While the substrate conversion lowered with catalyst in the order from monomer to third generation dendrimer, the second and third generation dendrimers themselves were found to exhibit significantly better catalytic activities than the monomer and the first generation dendrimer. Graphical abstract
- Krishna, Thatavarathy Rama,Jayaraman, Narayanaswamy
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p. 10325 - 10334
(2007/10/03)
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- Synthesis of erythro-α-Amino β-hydroxy Carboxylic Acid Esters by Diastereoselective Photocycloaddition of 5-Methoxyoxazoles with Aldehydes
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A new photoaldol route to α-amino-β-hydroxy carboxylic acid esters is initiated by the photocycloaddition of aromatic or aliphatic aldehydes to 5-methoxyoxazoles. The 4-unsubstituted 5-methyloxazole 1 gave the cycloadducts 8a-f in high yields and excellent exo-diastereoselectivities. Hydrolysis of 8a-f gives the N-acetyl α-amino-β-hydroxy esters 9a-f, which could be subsequently converted into the corresponding Z-didehydro α-amino acids 10a-f. Quartenary α-amino-β-hydroxy esters 12, 14, 16, 18, and 20, which are stable against dehydration, were obtained from the 4-alkylated 5-methoxyoxazoles 2-6, in most cases highly erythro-selective due to the high degree of stereocontrol (exo) at the photocycloaddition (to give 11, 13, 15, 17, and 19) level. The relative configurations of the N-acetyl α-amino-β-hydroxy esters were determined by NMR spectroscopy and comparison with chiral pool-derived compounds as well as by X-ray structure determination of the ester 23, formed by hydrolysis of the cycloadduct 22, derived from photocycloaddition of propionaldehyde to the isoleucine-derived oxazole 21.
- Griesbeck, Axel G.,Bondock, Samir,Lex, Johann
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p. 9899 - 9906
(2007/10/03)
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- Mechanism of asymmetric hydrogenation of α-(acylamino)acrylic esters catalyzed by BINAP-ruthenium(II) diacetate
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The mechanism of asymmetric hydrogenation of α-(acylamino)acrylic esters with Ru(CH3COO)2-[(S)-binap] (BINAP = 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl), giving the S saturated products in > 90% ee, has been investigated by means
- Kitamura, Masato,Tsukamoto, Masaki,Bessho, Yuhki,Yoshimura, Masahiro,Kobs, Uwe,Widhalm, Michael,Noyori, Ryoji
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p. 6649 - 6667
(2007/10/03)
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- Phosphonites based on the paracyclophane backbone: New ligands for highly selective rhodium-catalyzed asymmetric hydrogenation
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Figure presented The synthesis of new phosphonites with a chiral paracyclophane backbone is described. The rhodium complexes derived from the phosphonites bearing biphenoxy and binaphthoxy substituents are highly active and highly selective catalysts for the asymmetric hydrogenation of dehydroamino acids and esters.
- Zanotti-Gerosa, Antonio,Malan, Christophe,Herzberg, Daniela
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p. 3687 - 3690
(2007/10/03)
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- Synthesis of (P)- and (M)-6,7-bis[(diphenylphosphanyl)methyl]- 8,12diphenylbenzo[a]heptalenes - Potential ligands for homogeneous asymmetric catalysis
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The title bis(phosphane) ligands have been prepared starting from optically pure diisopropyl (P)- and (M)-8,12-diphenylbenzo[a]heptalene-6,7- dicarboxylates ((P)-1b and (M)-1b) that had been obtained by HPLC separation of rac-1b on a semi-preparative Chiralcel OD column. Reduction of (P)-1b and (M)-1b with diisobutylaluminum hydride (DIBAH) gave optically pure (P)- and (M)-dimethanols 3 (Scheme 6 and Fig. 5). Unfortunately, the almost quantitative chlorination of rac-3 with PCl5 in CHCl3 at - 60°led with (M)-3 to nearly complete loss of optical integrity. However, mesylate formation of (P)-3, followed by phosphanylation with LiP(BH3)Ph2 gave (P)-6 with only a small loss of optical activity. Optically pure (P)-6 was obtained by crystallization from Et2O/hexane, which removed the nearly insoluble rac- 6. The pure bis(phosphane) ligands (P)-2 and (M)-2 can be liberated quantitatively from 6 by warming 6 in toluene in the presence of 1,4- diazabicyclo[2.2.2]octane (DABCO). First Rh1-catalyzed asymmetric hydrogenation reactions of (Z)-a(acetamido)cinnamic acid ((Z)-14) in the presence of (P)-2 led to (R)-N-acetylphenylalanin ((R)-15) in optical purities up to 77% (see Table 1).
- Mohler, Peter,Rippert, Andreas Johannes,Hansen, Hans-Juergen
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p. 258 - 277
(2007/10/03)
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- An usual behaviour of ethers in presence of azlactones under ultrasound irradiation to give esters
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The phenomenon of ester formation from ethers and azlactones under sonolysis has been observed.
- Rajaram, S.,Lalitha, N.,Iyengar, D. S.
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p. 761 - 763
(2007/10/03)
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- A SIMPLE AND EFFICIENT "ONE-POT" SYNTHESIS OF 2-AZA-1,3-BUTADIENES FROM N-VINYLIC λ5-PHOSPHAZENES
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Reaction of N-vinylic λ5-phosphazenes (1) with acyl halides followed by addition of nucleophiles lead to 1-donor substituted 3-alkoxycarbonyl-2-aza-1,3-butadienes (2) with good to excellent yields.
- Barluenga, Jose,Ferrero, Miguel,Palacios, Francisco
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p. 3497 - 3500
(2007/10/02)
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- β-aryl and β-vinyl-αβ-didehydro-α-aminoacid derivatives through the palladium-catalysed reaction of aryl and vinyl triflates with methyl α-acetamidoacrylate
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Vinyl and aryl triflates react with methyl α-acetamidoacrylate in the presence of catalytic amounts of palladium to give β-vinyl and β-aryl-αβ-didehydro-α-aminoacid derivatives in good to high yields. A variety of reaction conditions were examined. Vinyl
- Arcadi,Cacchi,Marinelli,Morera,Ortar
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p. 7151 - 7164
(2007/10/02)
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- An interesting chloride ion effect in the Heck reaction
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Addition of chloride ion is found to enhance the yields of cross-couplings between aryl iodides and selected olefin acceptors.
- Merlic, Craig A.,Semmelhack, M.F.
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p. C23 - C27
(2007/10/02)
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- Palladium-Catalyzed Synthesis of Didehydroamino Acid Derivatives
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The palladium-catalyzed coupling of 2-amidoacrylates with aryl iodides under phase-transfer conditions yields aromatic (Z)-didehydroamino acid derivatives, which give various protected aromatic amino acids via catalytic hydrogenation using Pd/C or the Wil
- Carlstroem, Anne-Sofie,Frejd, Torbjoern
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p. 414 - 418
(2007/10/02)
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- Mechanism of the Hydrolysis of (Z)-4-Benzylidene-2-methyloxazolin-5-one or (Z)-4-Benzylidene-2-phenyloxazolin-5-one Derivatives
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The methyl (1a) and the phenyl (2) derivatives of (Z)-4-benzylideneoxazolin-5-one were hydrolyzed at comparable rates under alkaline conditions.In contrast, the acidic hydrolysis of 2 was at least 10E5 times slower than that of 1a.The Hammett ρ value obtained from the acidic hydrolysis of the phenyl substituted derivatives of 1a was 0.20 +/- 0.09 while that from the corresponding basic hydrolysis was 1.50 +/- 0.11.Methanolysis of 1a under basic conditions produced the methyl ester of (Z)-α-(acetylamino)cinnamic acid, and that under acidic conditions led to products consistent with the attack of methanol at the imine carbon.These results indicate that the alkaline hydrolysis of the oxazolin-5-one derivatives occurs through nucleophilic attack at the carbonyl carbon of the substrate and the acidic hydrolysis through that at the imine carbon.
- Suh, Junghun,Lee, Eun,Myoung, Young Chan,Kim, Minwoo,Kim, Soodan
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p. 977 - 980
(2007/10/02)
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- N-Acyl Dehydro-α-amino Acids from N-Formyl Dehydro-α-amino Acid Esters
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On treatment with methyl potassioisocyanoacetate (2), aldehydes and ketones 1 give N-anionized N-formyl dehydro-α-amino acid methyl esters 3.Compounds 3 with R1 = CH3, R2 = H is obtained by base induced ring opening of methyl 2-oxazoline-4-carboxylate 5. - Acylation of 3, followed by deformation of the intermediates 6, yields N-acyl dehydro α-amino acid methyl esters 7 which can be hydrolyzed to the N-acyl dehydro α-amino-acids 8.
- Schoellkopf, Ulrich,Meyer, Rolf
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p. 1469 - 1475
(2007/10/02)
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- Metal phosphine complex
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Group IB and IIB metal phosphine complexes are disclosed. These complexes are reacted with rhodium complex precursors to form useful enantioselective hydrogenation catalysts. Also disclosed is a method of preparing useful compounds having optical activity such as natural products and compounds useful as flavors and fragrances.
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