- The Enantioselective Dakin-West Reaction
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Here we report the development of the first enantioselective Dakin-West reaction, yielding α-acetamido methylketones with up to 58 % ee with good yields. Two of the obtained products were recrystallized once to achieve up to 84 % ee. The employed methylimidazole-containing oligopeptides catalyze both the acetylation of the azlactone intermediate and the terminal enantioselective decarboxylative protonation. We propose a dispersion-controlled reaction path that determines the asymmetric reprotonation of the intermediate enolate after the decarboxylation.
- Wende, Raffael C.,Seitz, Alexander,Niedek, Dominik,Schuler, S?ren M. M.,Hofmann, Christine,Becker, Jonathan,Schreiner, Peter R.
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p. 2719 - 2723
(2016/02/27)
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- Convenient method for reduction of C-N double bonds in oximes, imines, and hydrazones using sodium Borohydride-Raney ni system
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(Chemical Equation Presented) A practical method has been developed for reduction of C-N double bond in oximes, imines, and hydrazones with sodium borohydride catalyzed by Raney Ni. The reactions were carried out in basic aqueous solution, and the desired products were obtained in moderate yields after a simple procedure. This method can be applied to synthesize simpler aliphatic or aromatic amines and its analogs. Copyright Taylor & Francis Group, LLC.
- Yang, Yihua,Liu, Shouxin,Li, Junzhang,Tian, Xia,Zhen, Xiaoli,Han, Jianrong
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experimental part
p. 2540 - 2554
(2012/07/27)
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- Electron-donating and rigid p-stereogenic bisphospholane ligands for highly enantioselective rhodium-catalyzed asymmetric hydrogenations
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More electron donating, more rigid: A new highly electron-donating P-stereogenic bisphospholane ligand (ZhangPhos) was synthesized in a practical and highly enantioselective manner from a commercially available chiral source. Better or comparable enantioselectivities and reactivities than TangPhos were achieved in rhodium-catalyzed hydrogenation of various functionalized olefins (see scheme; nbd=3,5-norbornadiene). Copyright
- Zhang, Xiaowei,Huang, Kexuan,Hou, Guohua,Cao, Bonan,Zhang, Xumu
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supporting information; experimental part
p. 6421 - 6424
(2010/12/19)
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- CHIRAL PHOSPHORUS COMPOUNDS
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The present invention provides P-chiral compounds of general formula (II) and (III): wherein at least one of R21, R25, R26 and R30 is independently selected from C1-4 alkyl, CF3, C1-4 alkoxy, phenyl and benzyloxy and the remaining substituents selected from R21, R25, R26 and R30 are hydrogen; at least one of R22, R24, R27 and R29 are independently selected from C1-4 alkyl, CF3, C1-4 alkoxy, phenyl and benzyloxy and the remaining substituents selected from R22, R24, R27 and R29 are hydrogen; and R23 and R28 are independently selected from hydrogen, C1-4 alkyl, CF3, C1-4 alkoxy, phenyl and benzyloxy; Formula (III): wherein at least one of R21, R25, R26 and R30 is independently selected from phenyl and benzyloxy and the remaining substituents selected from R21, R25, R26 and R30 are hydrogen; and R22, R23, R24, R27, R28 and R29 are independently selected from hydrogen, C1-4 alkyl, CF3, C1-4 alkoxy, phenyl and benzyloxy.wherein at least one of R21, R25, R26 and R30 is independently selected from phenyl and benzyloxy and the remaining substituents selected from R21, R25, R26 and R30 are hydrogen; and R22, R23, R24, R27, R28 and R29 are independently selected from hydrogen, C1-4 alkyl, CF3, C1-4 alkoxy, phenyl and benzyloxy.
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Page/Page column 37-39
(2008/12/04)
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- Asymmetric catalysis based on chiral phospholanes and hydroxyl phospholanes
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Chiral phosphine ligands derived from chiral natural products including D-mannitol and tartaric acid. The ligands contain one or more 5-membered phospholane rings with multiple chiral centers, and provide high stereoselectivity in asymmetric reactions.
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Page column 22
(2010/02/06)
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- ASYMMETRIC SYNTHESIS CATALYZED BY TRANSITION METAL COMPLEXES WITH CYCLIC CHIRAL PHOSPHINE LIGANDS
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The present invention relates to rigid chiral ligands usefull in making catalysts for asymmetric synthesis. More particularly, the present invention relates to new monodentate and bidentate cyclic chiral phosphine ligands which are formed into catalysts to provide high selectivity of the enantiomeric structure of the end-product.
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- Novel phosphine-phosphite and phosphine-phosphinite ligands for highly enantioselective asymmetric hydrogenation
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Two novel phosphine-phosphite (S,R)-o-BINAPHOS and phosphine-phosphinite (S)-o-BIPNITE ligands based on ortho phenyl substituted (S)-BINOL have been synthesized. Extremely high enantioselectivity (over 99% ee in most cases) has been achieved for the Rh-catalyzed asymmetric hydrogenation of α-dehydroamino acid derivatives.
- Yan, Yongjun,Chi, Yongxiang,Zhang, Xumu
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p. 2173 - 2175
(2007/10/03)
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- Synthesis of ortho-phenyl substituted MeO-BIPHEP ligand and its application in Rh-catalyzed asymmetric hydrogenation
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A new BIPHEP-type ligand with phenyl groups at the 3,3′-positions, o-Ph-MeO-BIPHEP 3 was prepared. This ligand afforded excellent enantioselectivities when used in the Rh-catalyzed asymmetric hydrogenation of α-dehydroamino acid derivatives. The strong influence of o-phenyl groups of the ligand on the enantioselectivities of the reaction has been demonstrated by a comparison with its parent ligand MeO-BIPHEP.
- Wu, Shulin,He, Minsheng,Zhang, Xumu
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p. 2177 - 2180
(2007/10/03)
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- A Novel Chiral Ferrocenyl Phosphine Ligand from Sugar: Applications in Rh-Catalyzed Asymmetric Hydrogenation Reactions
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(Matrix Presented) A new chiral ferrocenyl diphosphine ligand 3 was synthesized from readily available D-mannitol. Rh-complex with this ligand showed high enantioselectivity and reactivity in the asymmetric hydrogenation of dehydroamino acid derivatives and itaconic acid derivatives. Up to over 99% ee and 10 000 TON were achieved with this catalytic system.
- Liu, Duan,Li, Wenge,Zhang, Xumu
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p. 4471 - 4474
(2007/10/03)
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- Asymmetric catalysis based on chiral phospholanes and hydroxyl phospholanes
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Chiral phosphine ligands derived from chiral natural products including D-mannitol and tartaric acid. The ligands contain one or more 5-membered phospholane rings with multiple chiral centers, and provide high stereoselectivity in asymmetric reactions.
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Page column 22
(2010/01/30)
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- A method for selective N-Boc deprotection on Wang resin
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A simple, inexpensive and efficient method for the selective cleavage of N-Boc protecting group under acidic conditions on high load Wang resin is described. This method employs the use of concd sulfuric acid in 1,4-dioxan and provides an efficient process for the complete Boc deprotection with minimal loss of substrate through cleavage from resin.
- Trivedi,Anson,Steel,Worley
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p. 1932 - 1934
(2007/10/03)
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- Synthesis of chiral hydroxyl phospholanes from D-mannitol and their use in asymmetric catalytic reactions
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Chiral hydroxyl monophosphane 3 [(2S,3S,4S,5S)-3,4-dihydroxy-2,5-dimethyl-1-phenylphospholane] and bisphospholanes 5a [1,2-bis[(2S,3S,4S,5S)-3,4-dihydroxy-2,5-dimethylphospholanyl]benzene] and 5b [1,2-bis[(2S,3S,4S,5S)-2,5-diethyl-3,4-dihydroxyphospholanyl]benzene] were synthesized from readily available D-mannitol in high yields. Strategies for protection and deprotection of OH-groups in the presence of phosphines have been explored. Rate acceleration in the Baylis - Hillman reaction was observed when a hydroxyl phosphine was used as the catalyst. Rhodium complexes with chiral bisphospholanes are highly enantioselective catalysts for the asymmetric hydrogenation of various kinds of functionalized olefins such as dehydroamino acid derivatives, itaconic acid derivatives, and enamides. An interesting feature of the hydroxyl phospholane system is that hydrogenation of some substrates can be carried out in water with >99% ee and 100% conversion (e.g., itaconic acid).
- Li, Wenge,Zhang, Zhaoguo,Xiao, Dengming,Zhang, Xumu
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p. 3489 - 3496
(2007/10/03)
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- Variations of the Nature of the Chiral Auxiliary with a Highly Enantioselective Chiral NADH Model
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Various chiral amine alcohols have been used as chiral auxiliares for a highly enantioselective NADH model.Some of these are new reagents which have been obtained by an enzymic resolution method.
- Combret, Yves,Duflos, Jack,Dupas, Georges,Bourguignon, Jean,Queguiner, Guy
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p. 1635 - 1644
(2007/10/02)
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- Synthesis and biological activities of cholecystokinin analogues substituted in position 30 by 3-(1-naphthyl)-L-alanine [Nal(1)] or 3-(2-naphthyl)-L-alanine [Nal(2)]
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Acetyl derivatives of ethyl esters of 3-(1-naphthyl)-D,L-alanine and 3-(2-naphthyl)-D,L-alanine were synthesized through a malonic condensation. Resolution of these derivatives by subtilisin Carlsberg followed by acid hydrolysis afforded the 2 optical isomers of 3-(1-naphthyl)-alanine [Nal(1)] and 3-(2-naphthyl)-alanine [Nal(2)]. The L enantiomers of these amino acids were incorporated into the sequence of cholecystokinin in place of the tryptophan in position 30. The cholecystokinin analogues thus obtained behaved as full agonists, with reduced potencies on rat pancreatic acini and on guinea pig brain membranes, by about one order of magnitude for the Nal(1) derivative, as compared to the potent parent compound Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-Asp-Phe-NH2.
- Rodriguez,Bernad,Galas,Lignon,Laur,Aumelas,Martinez
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p. 245 - 253
(2007/10/02)
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- Nonapeptide and decapeptide analogs of LHRH, useful as LHRH antagonists
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Nonapeptide and decapeptide analogs of LHRH which have the formula: STR1 and the pharmaceutically acceptable salts thereof, wherein: X is a D-alanyl residue wherein one hydrogen on C-3 is replaced by:(a) a carbocyclic aryl-containing radical selected from the group consisting of phenyl substituted with three or more straight chain lower alkyl groups, naphthyl, anthryl, fluorenyl, phenanthryl, biphenylyl and benzhydryl; or(b) a saturated carbocyclic radical selected from the group consisting of cyclohexyl substituted with three or more straight chain lower alkyl groups, perhydronaphthyl, perhydrobiphenylyl, perhydro-2,2-diphenylmethyl, and adamantyl; or(c) a heterocyclic aryl containing radical selected from the group consisting of radicals represented by the following structural formulas: STR2 wherein A"" and A'' are independently selected from the group consisting of hydrogen, lower alkyl, chlorine, and bromine, and G is selected from the group consisting of oxygen, nitrogen, and sulfur;A is an aminoacyl residue selected from the group consisting of L-pyroglutamyl, D-pyroglutamyl, N-acyl-L-prolyl, N-acyl-D-prolyl, N-acyl-D-tryptophanyl, N-acyl-D-phenylalanyl, N-acyl-D-p-halophenylalanyl, and N-acyl-X wherein X is as defined previously;B is an amino acyl residue selected from the group consisting of D-phenylalanyl, D-p-halophenylalanyl, 2,2-diphenylglycyl, and X wherein X is as defined previously;C is an amino acyl residue selected from the group consisting of L-tryptophanyl, D-tryptophanyl, D-phenylalanyl and X wherein X is as defined above;E is glycinamide or --NH--R 1, wherein R 1 is lower alkyl, cycloalkyl, fluoro lower alkyl or STR3 wherein R 2 is hydrogen or lower alkyl; are disclosed. These compounds are LHRH antagonists.
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