- 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
-
supporting information
p. 13365 - 13368
(2021/12/17)
-
- Rh(III)-Catalyzed Three-Component Syn-Carboamination of Alkenes Using Arylboronic Acids and Dioxazolones
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Herein, we report a Rh(III)-catalyzed three-component carboamination of alkenes from readily available aryl boronic acids as a carbon source and dioxazolones as nitrogen electrophiles. This protocol provides facile access to valuable amine products including α-amino acid derivatives in good yield and regioselectivity without the need for a directing functionality. A series of experiments suggest a mechanism in which the Rh(III) catalyst undergoes transmetalation with the aryl boronic acid, followed by turnover limiting alkene migratory insertion into the Rh(III)-aryl bond. Subsequently, fast Rh-nitrene formation provides the syn-carboamination product selectively after reductive elimination and proto-demetalation. Importantly, the protocol provides three-component coupling products in preference to a variety of two-component undesired byproducts.
- Lee, Sumin,Rovis, Tomislav
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p. 8585 - 8590
(2021/07/26)
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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
-
supporting information
p. 9642 - 9652
(2020/07/02)
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- New chiral ferrocene/indole-based diphosphine ligands for Rh-catalyzed asymmetric hydrogenation of functionalized olefins
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Convenient synthesis of a new family of chiral ferrocene/indole-based diphosphine ligands, (Rc,Rp)-IndoFerroPhos (L), from (Sc,Rp)-PPFA and 2-(diphenylphosphino)indole has been described. These new ligands exhibited high efficiency in the Rh-catalyzed asymmetric hydrogenation of functionalized olefins including α-dehydroamino acid esters, α-enamides and dimethyl itaconate, in which up to >99% yield and 98% ee were achieved.
- Abbas, Zaheer,Ali, Aijaz,Hu, Xiang-Ping,Hu, Xin-Hu,Xu, You-Wei
-
-
- Synthesis of constrained tetracyclic peptides by consecutive CEPS, CLIPS, and oxime ligation
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In Nature, multicyclic peptides constitute a versatile molecule class with various biological functions. For their pharmaceutical exploitation, chemical methodologies that enable selective consecutive macrocyclizations are required. We disclose a combination of enzymatic macrocyclization, CLIPS alkylation, and oxime ligation to prepare tetracyclic peptides. Five new small molecular scaffolds and differently sized model peptides featuring noncanonical amino acids were synthesized. Enzymatic macrocyclization, followed by one-pot scaffold-assisted cyclizations, yielded 21 tetracyclic peptides in a facile and robust manner.
- Streefkerk, Dieuwertje E.,Schmidt, Marcel,Ippel, Johannes H.,Hackeng, Tilman M.,Nuijens, Timo,Timmerman, Peter,Van Maarseveen, Jan H.
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supporting information
p. 2095 - 2100
(2019/04/11)
-
- Synthesis and preliminary anti-inflammatory and anti-bacterial evaluation of some diflunisal aza-analogs
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Our aim was to identify new multi-target compounds endowed with both anti-inflammatory and anti-bacterial activities for treatment of human infections. Diflunisal, a nonsteroidal anti-inflammatory agent, has recently been repurposed for its anti-virulence properties against methicillin-resistant Staphylococcus aureus. Effective synthesis of some aza-analogs of the anti-inflammatory drug diflunisal was carried out following the route involving key oxazole intermediates to obtain o- and m-hydroxypyridinecarboxylic acid derivatives. The newly synthesized diflunisal aza-analogs did not exhibit cytotoxic activity up to 80 μM and some of them exhibited anti-inflammatory activities, decreasing the levels of pro-inflammatory cytokines and prostaglandins induced by bacterial lipopolysaccharide in human primary macrophages. Ten of the diflunisal aza-analogs were found to have interesting antibacterial activity, sensitizing S. aureus, Streptococcus pyogenes, Enterococcus faecium, and Pseudomonas aeruginosa to the antibacterial effects of beta-lactam antibiotics and protein synthesis inhibitors.
- Carta, Davide,Brun, Paola,Dal Pra, Matteo,Bernabè, Giulia,Castagliuolo, Ignazio,Ferlin, Maria Grazia
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p. 1017 - 1032
(2018/06/27)
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- Ultrasound-Promoted Enantioselective Decarboxylative Protonation of α-Aminomalonate Hemiesters by Chiral Squaramides: A Practical Approach to Both Enantiomers of α-Amino Esters
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Herein, we report an ultrasound-promoted enantioselective decarboxylative protonation reaction of α-aminomalonate hemiesters 1 in the presence of chiral cinchona-derived squaramide Br?nsted bases under mild conditions, which afforded both the (S)- and (R)-enantiomers of α-amino acid derivatives 2 in excellent yields (> 90 %) and excellent enantioselectivities (up to 98 % ee).
- Some, Surajit,Bae, Han Yong,Kim, Mun Jong,Zhang, Yong Jian,Song, Choong Eui
-
supporting information
p. 4562 - 4565
(2017/08/30)
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- Thioamide-substituted cinchona alkaloids as efficient organocatalysts for asymmetric decarboxylative reactions of MAHOs
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A new class of thioamide-substituted cinchona derivatives is reported. A convergent and practical approach was developed to insert the thioamide functional group onto the cinchonidine from readily available dithioesters. These organocatalysts were effective in asymmetric decarboxylative Mannich and protonation reactions of α-amido-substituted malonic acid half oxyesters (MAHOs), affording α,β- and α-amino acid derivatives, respectively, in good yields and stereoselectivities.
- Singjunla, Yuttapong,Pigeaux, Morgane,Laporte, Romain,Baudoux, Jér?me,Rouden, Jacques
-
supporting information
p. 4319 - 4320
(2018/08/24)
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- Towards a universal organocatalyst for the synthesis of enantioenriched phenylalanine derivatives by enantioselective decarboxylative protonation
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Access to enantioenriched non-proteogenic phenylalanine derivatives is described using the enantioselective decarboxylative protonation reaction of amidohemimalonate esters catalysed by various cinchona-based compounds. This study compares the catalytic efficiency as well as the enantioselectivity induced by three types of common organocatalysts, namely thioureas, squaramides and bis-cinchona squaramides. One of the main outcome of this work is the observation of a significant influence of the N-protecting group of the hemimalonate on its interaction with the catalyst. This methodology carried out under mild conditions exhibits good substrate scope and functional group tolerance. A substoichiometric amount of catalyst can also be used in certain cases while affording good yields and selectivities.
- Pigeaux, Morgane,Laporte, Romain,Harrowven, David C.,Baudoux, Jér?me,Rouden, Jacques
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p. 4599 - 4603
(2016/09/23)
-
- Urea treated subtilisin as a biocatalyst for transformations in organic solvents
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Abstract Subtilisin lyophilized from its solution in aqueous buffer in the presence of 6 M urea showed up to 50-fold increase (as compared to lyophilized subtilisin not subjected to urea treatment) in its initial rate of a transesterification reaction in anhydrous n-hexane. The lyophilization time controlling the extent of 'drying' was an important parameter. The urea treated subtilisin had five times shorter half life during heating at 100 C in hexane. The change in conformation was also reflected in its 92-fold higher activity at 15 C as compared to merely 28-fold higher activity at 45 C. The comparative enantioselectivity of urea treated subtilisin during kinetic resolution of 1-phenylethanol was expectedly lower. Its enantioselectivity during kinetic resolution of a natural substrate N-acetyl-(R,S)-phenylalanine ethyl ester in hexane was higher. Urea treated subtilisin also showed higher catalytic promiscuity during an aldol condensation. CD studies in both far UV and near UV region were also carried out to compare the two structures.
- Mukherjee, Joyeeta,Mishra, Prasant,Gupta, Munishwar N.
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p. 1976 - 1981
(2015/03/30)
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- An eco-benign and highly efficient procedure for N-acylation catalyzed by heteropolyanion-based ionic liquids using carboxylic acid under solvent-free conditions
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An eco-benign and highly efficient route for N-acylation of amines has been developed by treating amines with corresponding carboxylic acids in the presence of 2 mol % of heteropolyanion-based ionic liquids as catalysts under solvent-free conditions. This practical reaction could tolerate a wide range of substrates. Thus, various N-acylation products including N-acyl α-amino acid derivatives were obtained in moderate to excellent yields at 70 C to 120 C. Moreover, recycling studies revealed that heteropolyanion-based ionic liquids were easily reusable for this N-acylation. This method provides a green and much improved protocol over the existing methods.
- Chen, Zhikai,Fu, Renzhong,Chai, Wen,Zheng, Hao,Sun, Lin,Lu, Qiang,Yuan, Rongxin
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p. 2237 - 2245
(2014/03/21)
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- β-Amino esters from the reductive ring opening of aziridine-2-carboxylates
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A general study is undertaken to examine the scope of the reductive ring opening of aziridine-2-carboxylates with samarium diiodide. The competition between C-C and C-N bond cleavage is examined as a function of the nature of the N-substituent of the aziridine, the nature of the substituent in the 3-position of the aziridine, and whether the substituent in the 3-position is in a cis or trans relationship with the carboxylate in the 2-position. The desired C-N bond cleavage leads to β-amino esters that are the predominant products for most aziridines with an N-activating group. However, C-C cleavage products are observed with an aryl group in the 3-position; this can be particularly pronounced with cis-aziridines where a nearly equal mixture of the two is observed. Exclusive formation of the C-N cleavage product is observed for all aziridines with the strongly N-activating p-toluene sulfonate group. Similarly high selectivity is observed for the 2-trimethylsilylethyl sulfonate group (SES), which is easier to remove. The utility of these methods is illustrated in the synthesis of protected forms of (R)-β3-DOPA and l-DOPA from the same aziridine, the former by SmI2-mediated reductive opening at C-2 and the latter by palladium-mediated reductive opening at C-3.
- Zhao, Wenjun,Lu, Zhenjie,Wulff, William D.
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p. 10068 - 10080
(2015/02/19)
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- Self-disproportionation of enantiomers of non-racemic chiral amine derivatives through achiral chromatography
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Efficient self-disproportionation of enantiomers of several non-racemic chiral amines was achieved through conversion to N-acetamides and subsequent MPLC using an achiral column. The MPLC of these non-racemic N-acetamide derivatives gave the chart having a clear boundary between two fractions. Thus, in the less polar fraction, remarkable enantiomer enrichment was observed (>99%ee), while the ee of more polar fraction was considerably reduced. The magnitude of the enantiomer enrichments and depletions strongly depended on substituent on the amino group.
- Nakamura, Tsuyoshi,Tateishi, Kaori,Tsukagoshi, Shiori,Hashimoto, Saori,Watanabe, Shotaro,Soloshonok, Vadim A.,Ace?a, José Luis,Kitagawa, Osamu
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experimental part
p. 4013 - 4017
(2012/07/14)
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- Resolution of N-protected amino acid esters using whole cells of Candida parapsilosis ATCC 7330
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Whole cells of Candida parapsilosis ATCC 7330 were used for the resolution of N-acetyl amino acid esters. Excellent enantioselectivities (E = 40 to >500) were achieved for the resolution of N-protected protein and non-protein amino acid esters giving good yields (28-50%) and high enantiomeric excesses (up to >99%) for both enantiomers.
- Stella, Selvaraj,Chadha, Anju
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experimental part
p. 457 - 460
(2010/06/21)
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- A chiral bidentate phosphoramidite (Me-BIPAM) for Rh-catalyzed asymmetric hydrogenation of α-dehydroamino esters, enamides, and dimethyl itaconate
-
High performance of Me-BIPAM for enantioselective hydrogenation of α-dehydroamino esters, enamides, and dimethyl itaconate was demonstrated. [Rh(Me-BIPAM)(diene)]X (diene = cod, nbd; X = BF4, PF6, SbF6) gave optically active β-aryl α-amino esters up to 99% ee, 1-arylethylamines up to 97% ee, methyl 2-acetylaminobutanoate with 90% ee, and dimethyl 2-methylsuccinate with 97% ee under 0.3-0.8 MPa dihydrogen with 0.1-1 mol % catalyst loading.
- Kurihara, Kazunori,Yamamoto, Yasunori,Miyaura, Norio
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experimental part
p. 3158 - 3160
(2009/08/09)
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- Novel chiral phosphine-phosphoramidite ligands derived from 1-naphthylamine for highly efficient Rh-catalyzed asymmetric hydrogenation
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A new chiral phosphine-phosphoramidite ligand (S)-HY-Phos 1 has been prepared from 1-naphthylamine via a two-step transformation, and successfully applied in the Rh-catalyzed asymmetric hydrogenation of various functionalized olefins, including α-(acetamido)cinnamates, enamides and α-enol ester phosphonates, in which up to 98% ee, 99% ee and 99% ee were achieved, respectively.
- Yu, Sai-Bo,Huang, Jia-Di,Wang, Dao-Yong,Hu, Xiang-Ping,Deng, Jun,Duan, Zheng-Chao,Zheng, Zhuo
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p. 1862 - 1866
(2008/12/21)
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- Highly enantioselective decarboxylative protonation of α- aminomalonates mediated by thiourea Cinchona alkaloid derivatives: Access to both enantiomers of cyclic and acyclic α-aminoacids
-
Equation Presented Thiourea derived cinchona alkaloids promote the asymmetric decarboxylase protonation of cyclic, acyclic, or bicyclic α-aminomalonate hemiesters under mild and metal-free conditions to afford enantioenriched aminoesters in high yields and enantioselectivities up to 93%. Both enantiomers of the aminoesters have been synthesized with the same selectivity when using organic base 3 and its pseudoenantiomer 6 derived from quinine.
- Amere, Mukkanti,Lasne, Marie-Claire,Rouden, Jacques
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p. 2621 - 2624
(2008/02/10)
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- Unsymmetrical ferrocenylethylamine-derived monophosphoramidites: Highly efficient chiral ligands for Rh-catalyzed enantioselective hydrogenation of enamides and α-dehydroamino acid derivatives
-
A new family of unsymmetrical ferrocenylethylamine-derived monophosphoramidites were synthesized and successfully applied in the Rh-catalyzed enantioselective hydrogenation of a range of enamides and α-dehydroamino acid esters, and ee values of up to 99.5% were obtained for both types of substrate. These results suggest that unsymmetrical amine-derived monophosphoramidites can also exhibit excellent enantioselectivity for a broad range of substrates, comparable to or higher than those of the most efficient symmetrical amine-derived monophosphoramidites reported thus far.
- Zeng, Qing-Heng,Hu, Xiang-Ping,Duan, Zheng-Chao,Liang, Xin-Miao,Zheng, Zhuo
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p. 393 - 396
(2007/10/03)
-
- ANTI-ODOR COMPOSITIONS AND THERAPEUTIC USE
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This application discloses a composition comprising a malodor compound and an anti-odor ingredient effective for reducing the presence or production of malodor. The composition may be topically applied to a subject and is useful for cosmetic conditions, pharmaceutical indications, or other objectives.
- -
-
-
- New unsymmetrical hybrid ferrocenylphosphine-phosphoramidite ligands derived from H8-BINOL for highly efficient Rh-catalyzed enantioselective hydrogenation
-
A series of new H8-BINOL-derived unsymmetrical hybrid ferrocenylphosphine-phosphoramidite ligands have been synthesized and successfully used in Rh-catalyzed asymmetric hydrogenations. The same or higher enantioselectivities (99.9% ee) were achieved in the hydrogenation of dimethyl itaconate and α-dehydroamino acid esters as those obtained with BINOL-derived analogues. However, slightly lower enantioselectivities (99.0% ee) were obtained in the hydrogenation of enamides.
- Zeng, Qing-Heng,Hu, Xiang-Ping,Duan, Zheng-Chao,Liang, Xin-Miao,Zheng, Zhuo
-
p. 1233 - 1238
(2007/10/03)
-
- α-amino acid derivatives by enantioselective decarboxylation
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The methodology of enantioselective decarboxylation was applied to 2-aminomalonic acid derivatives in order to obtain enantio-enriched amino acid derivatives. Full conversion was achieved stirring racemic N-acetylated 2-aminomalonic hemiesters in THF at 70 °C with 10 mol % of a chiral base for 24 h. The catalyst may be recycled. Whereas the commercially available cinchona alkaloids gave poor results, benzamide and benzenesulfonamide derivatives of 9-amino(9-deoxy)epicinchonine turned out to be effective catalysts. The best result was obtained with 2-N-acetylamino-2-ethoxy-carbonyl-3-phenylpropionic acid as the starting material and N-(9-deoxyepicinchonine-9-yl)-4-methoxybenzamide as the chiral base to give ethyl N-acetyl-L-phenylalaninate in 70% ee. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.
- Brunner, Henri,Baur, Markus A.
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p. 2854 - 2862
(2007/10/03)
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- The enzyme-catalysed stereoselective transesterification of phenylalanine derivatives in supercritical carbon dioxide
-
The subtilisin Carlsberg catalysed transesterification of N-acetyl phenylalanine methyl ester (1), N-acetyl phenylalanine ethyl ester (2), N-trifluoroacetyl phenylalanine methyl ester (3) and N-trifluoroacetyl phenylalanine ethyl ester (4) was studied in supercritical carbon dioxide. The water content of the reaction affects the reactivity of the system; for the transesterification of the methyl esters with ethanol the optimum concentration of water was determined to be about 0.74 M, while for the transesterification of the ethyl esters with methanol the optimum concentration of water was about 1.3 M. The conversion is also dependent upon the concentration of alcohol; for ethanol, 2% v/v gives the maximum conversion, whilst for methanol, only 0.8-1. 2% v/v is required. This is probably due to a difference in the solubility of the substrates in the two alcohol/supercritical carbon dioxide mixtures. The reaction is highly stereoselective, in all cases no evidence for reaction of the D-isomer could be detected by chiral gas chromatography.
- Smallridge, Andrew J.,Trewhella, Maurie A.,Wang
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p. 259 - 262
(2007/10/03)
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- A new family of chelating diphosphines with a transition metal stereocenter in the backbone: Novel applications of "chiral-at-rhenium" complexes in rhodium-catalyzed enantioselective alkene hydrogenations
-
The title compounds are accessed by sequences starting with racemic and enantiomerically pure [(η5-C5H5)Re(NO)(PPh3) (CH3)]. Reactions with chlorobenzene/HBF4, PPh2H, and tBuOK give the phosphido complex [(η5-C5H5)Re(NO) (PPh3)(PPh2)] (3). Reactions with Ph3C+BF4-,PPh2H, and tBuOK give the methylene homologue [(η5-C5H5)Re(NO)(PPh3) (CH2PPh2)] (9). Treatment of 3 or 9 with nBuLi or tBuLi and then PPh2Cl gives the diphosphido systems [(η5-C5H4PPh2)Re(NO) (PPh3)-((CH2)nPPh2)] (n = 0/1, 5/11). Reactions of 5 and 11 with [Rh(NBD)Cl]2/AgPF6 (NBD = norbornadiene) give the rhenium/rhodium chelate complexes [(η5-C5H4-PPh2)Re(NO) (PPh3)((μ-CH2)nPPh 2)Rh-(NBD)]+PF6- (n = 0/1, 6+/12+ PF6-; 30-32% overall from commercial Re2(CO)10). The crystal structures of 6+ PF6- and 12+ PF6- are compared to those of 3 and 9, and other rhodium complexes of chelating bis(diphenylphosphines). The chiral pockets defined by the PPh2 groups show unusual features. Four alkenes of the type (Z)-RCH=C(NHCOCH3)CO2R′ are treated with H2 (1 atm) and (R)-6+ PF6- or (S)-12+ PF6- (0.5 mol%) in THF at room temperature. Protected amino acids are obtained in 70-98% yields and 93-82 % ee [(R)-6+ PF6-] or 72-60% ee [(S)-12+ PF6- ]. Pressure and temperature effects are defined, and turnover numbers of > 1600 are realized.
- Kromm, Klemenz,Zwick, Bill D.,Meyer, Oliver,Hampel, Frank,Gladysz, John A.
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p. 2015 - 2027
(2007/10/03)
-
- New chiral diphosphinites: Synthesis of Rh complexes. Heterogenisation on zeolites
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New diphosphinite ligands derived from (2S,4R), (2S,4S)-1-benzyl-4-hydroxy-4-phenyl-2-(1,1-diphenylmethyl)pyrrolidinylmethanol and (2S,4R), (2S,4S)-1-(3-triethoxysilyl)propylaminocarbonyl-4-hydroxy-4-phenyl-2-(1,1- diphenylmethyl)pyrrolidi nylmethanol have been prepared in high yields (60-80%) and reacted with [RhCl(cod)]2 to yield cationic [Rh(diphosphinite)(cod)]+ complexes. Those metal complexes bearing a triethoxysilyl group were covalently bonded to USY-zeolite by controlled hydrolysis and Rh-heterogenised complexes were obtained. A comparative study (homogeneous versus supported) for the catalytic activity and selectivity in hydrogenation and hydroformylation reactions was made, obtaining an enhanced performance for heterogenised catalysts; moreover, those catalysts can be recycled in successive runs, by a simple filtration, without a significant loss of activity.
- Fuerte,Iglesias,Sanchez
-
p. 186 - 194
(2007/10/03)
-
- Heterogenised catalysts on zeolites. Synthesis of new chiral Rh(I) complexes with (2S,4R)-trans-4-RCOO-2-(t-butylaminocarbonyl) pyrrolidines and (2S,4S)-cis-4-RCONH-2-(t-butylaminocarbonyl) pyrrolidines. Heterogenisation on silica and a USY-zeolite and study of the role of support on their catalytic profile in hydrogenation of olefins
-
Novel chiral ligands (2S,4R)-2-(t-butylaminocarbonyl)-4-[3-(alkylaminocarbonyl)propanoyloxy]pyrrolidine and (2S,4S)-cis-4-(alkylaminocarbonylamino)-2-(t-butyl-aminocarbonyl)pyrrolidine (4a,b; 9a,b), (a: alkyl = t-butyl; b: alkyl = 3-triethoxysilylpropyl) and their rhodium complexes were synthesised and characterised. The reactions of [{Rh(cod)Cl}2] and [RhCl(PPh3)3] with the chiral ligands in the presence of a non-coordinating anion (PF-6) gave the cationic complexes [Rh(L2)(ligand)][PF6] (L2 = cod, PPh3). The structures of these complexes were elucidated by elemental analyses, IR spectroscopy and 1H, 13C and 31P NMR measurements. The metal complexes bearing a triethoxysilyl group were covalently bonded to silica and modified USY-zeolite and Rh-heterogenised complexes were obtained. A comparative study (homogeneous versus supported) was made for the catalytic activity in hydrogenation reactions.
- Corma,Iglesias,Mohino,Sanchez
-
p. 147 - 156
(2007/10/03)
-
- Selectivity and Specificity in Substrate Binding to Proteases: Novel Hydrolytic Reactions Catalysed by α-Chymotrypsin Suspended in Organic Solvents with Low Water Content and Mediated by Ammonium Hydrogen Carbonate
-
α-Chymotrypsin suspended in organic solvents with low water content catalysed hydrolytic reactions in the presence of ammonium hydrogen carbonate.Molecular modelling studies were carried out and structure-reactivity relationships were established by studying the hydrolysis of amino acid derivatives and analogues.The enzyme was found to be stereoselective with respect to the hydrolysis of L-amino acid derivatives, but no stereoselectivity was observed when α-hydroxy esters were used as substrates.A general procedure for the resolution of aromatic amino acid esters is given.The results are interpreted in terms of molecular modelling based on X-ray crystallographic data and literature data.
- Ricca, Jean-Marc,Crout, David H. G.
-
p. 1225 - 1234
(2007/10/02)
-
- New Rhodium Complexes anchored on Modified USY Zeolites. A Remarkable Effect of the Support on the Enantioselectivity of Catalytic Hydrogenation of Prochiral Alkenes
-
Rh-complexes with N-based chiral ligands, when anchored on a modified USY-zeolite which contains profuse supermicropores, produce a remarkable increase of enantioselectivity (>95percent) in the hydrogenation of N-acyldehydrophenylalanine derivatives and represent a truly heterogeneous counterpart of the homogeneous organometallic catalysts.
- Corma, A.,Iglesias, M.,Pino, C. del,Sanchez, F.
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p. 1253 - 1255
(2007/10/02)
-
- Asymmetric Hydrogenation Using Diphenylphosphinite Derivatives of Carbohydrates as the Chiral Ligand of Rhodium Catalysts
-
Diphenylphosphinite derivatives of carbohydrates (L-rhamnose, D-mannitol, and cellulose), which have asymmetric centers on the skeletons were synthesized.Asymmetric hydrogenations of prochiral substrates using rhodium catalysts with the prepared chiral phosphinite ligand were carried out to obtain chiral substances in 8-78percent optical yield.
- Yamashita, Mitsuji,Naoi, Manabu,Imoto, Hiroyuki,Oshikawa, Tatsuo
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p. 942 - 944
(2007/10/02)
-
- BIOCATALYTICAL TRANSFORMATIONS II. ENANTIOSELECTIVE HYDROLYSIS OF N-ACETYL-FLUORO-PHENYLALANINE-ETHYLESTERS BY LYOPHILISED YEAST
-
The three nuclear substituted monofluoro D-N-acetylphenylalanine-ethylesters were obtained in excellent yield via enantioselective hydrolysis of their respective racemates by use of lyophilised yeast (Saccharomyces cerevisiae Hansen).
- Csuk, Rene,Glaenzer, Brigitte I.
-
-
- ENANTIOSELECTIVE HYDROLYSIS BY BAKER'S YEAST - II. ESTERS OF N-ACETYL AMINO ACIDS
-
D-N-Acetyl amino acid esters were obtained via enantioselective hydrolysis of their racemates by use of fermenting yeast.Evidence is given that proteinases are the enzymes involved.
- Glaenzer, B. I.,Faber, K.,Griengl, H.
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p. 771 - 778
(2007/10/02)
-
- ENANTIOSELECTIVE HYDROLYSIS BY BAKER'S YEAST
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Optically active N-acetylamino acid esters were obtained by enantioselective hydrolysis of their racemates using fermenting baker's yeast.
- Glaenzer, B.I.,Faber, K.,Griengl, H.
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p. 4293 - 4294
(2007/10/02)
-
- Synthesis of Sugar Derivatives of Tervalent Phosphorus Compounds and Their Application to Homogeneous Asymmetric Hydrogenation
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Diphenylphosphine and diphenylphosphinite derivatives of sugars such as methyl 6-deoxy-4-C-(diphenylphosphino)-2,3-O-isopropylidene-α-L-talopyranoside, methyl 4-O-(diphenylphosphino)-2,3-O-isopropylidene-α-L-rhamnopyranoside, methyl 4-C,4-O-(diphenylphosphino)-2,3-O-isopropylidene-α-L-talopyranoside, 6-deoxy-6-C-(diphenylphosphino)-1,2:3,5-di-O-isopropylidene-α-D-glucofuranose, and 6-O-(diphenylphosphino)-1,2:3,4-di-O-isopropylidene-α-D-galactopyranose were synthesized by the reaction of diphenylphosphine-sodium dihydrobis(2-methoxyethoxy)aluminate (SDMA) and/or diphenylphosphinous chloride-triethylamine with sugar derivatives.Homogeneous asymmetric hydrogenations of several prochiral olefins (α-acetylaminocinnamic acid, methyl α-acetylaminocinnamate, α-benzoylaminocinnamic acid, itaconic acid, and tiglic acid) were carried out using rhodium(I) catalysts with the tervalent chiral phosphorus derivatives of sugars.The highest optical yield for all the five substrates was obtained when di-μ-chloro-bis(cyclooctadiene)dirhodium(I) and 6-O-(diphenylphosphino)-1,2:3,4-di-O-isopropylidene-α-D-galactopyranose were used.The advantages of this method are the simplicity in the synthesis of the chiral phosphorus compound and the comparatively high optical yield in the asymmetric hydrogenation of olefins.
- Yamashita, Mitsuji,Hiramatsu, Koji,Yamada, Manabu,Suzuki, Nobuyoshi,Inokawa, Saburo
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p. 2917 - 2921
(2007/10/02)
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