- Combination of the Lipase-Catalysed Resolution with Mitsunobu Esterification in One Pot
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A chemo-enzymatic method for the preparation of homochiral esters of 14 secondary alcohols with 100percent theoretical yields is described in one pot through two steps: the lipase-catalysed kinetic resolution followed by the Mitsunobu esterification of the free alcohol enantiomer in situ in the resolution mixture.Mathematical equations which link the enzymatic and chemical steps were derived, resulting in an enantioconvergent synthetic tool for the preparation of chiral intermediates.
- Vaenttinen, Eero,Kanerva, Liisa T.
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- Asymmetric Cyanosilylation of Aldehydes by a Lewis Acid/Base Synergistic Catalyst of Chiral Metal Clusters
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Metal clusters with well-defined crystal structures are extremely useful for studying the synergistic catalytic effects and associated catalytic mechanisms. In this study, two pairs of chiral lanthanide-transition metal clusters (R)/(S)-Co3Ln2(Ln = Tb or Dy) were synthesized using Schiff-base ligands [(R)- or (S)-H3L] with multiple Lewis base sites (O sites). The as-prepared (R)/(S)-Co3Ln2chiral metal clusters exhibited good catalytic functionality in the asymmetric synthesis of chiral cyanohydrins, with high conversions of up to 99% and medium-to-high enantiomeric excess values of up to 78%. The catalysis process followed a mechanism in which the bifunctional metal clusters of (R)/(S)-Co3Ln2, containing Lewis acid sites and Lewis base sites, simultaneously activated the aldehydes and trimethylsilyl cyanide, respectively. Consequently, synergistic catalysis was realized. The enantioselectivity of the different aldehydes and stereochemical configuration of the resulting products are attributed to the formation of a steric chiral pocket via the external chiral ligands on the clusters. In addition, heterogeneous asymmetric cyanosilylation using (R)/(S)-Co3Ln2chiral metal clusters achieved high chemoselectivity and regioselectivity under mild conditions.
- Huang, Kai-Xin,Kong, Xiang-Jian,Li, Jun-Ping,Long, La-Sheng,Weng, Zhen-Zhang,Xie, Jing,Zheng, Lan-Sun
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p. 4121 - 4129
(2022/03/09)
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- Palladium-catalyzed C-H activation of simple arenes and cascade reaction with nitriles: access to 2,4,5-trisubstituted oxazoles
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An efficient and straightforward protocol for the assembly of the pharmaceutically and biologically valuable oxazole skeleton is achieved for the first time from readily available simple arenes and functionalized aliphatic nitriles. This transformation in
- Dai, Ling,Yu, Shuling,Shao, Yinlin,Li, Renhao,Chen, Zhongyan,Lv, Ningning,Chen, Jiuxi
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supporting information
p. 1376 - 1379
(2021/02/22)
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- Synthesis of Imidazoles and Oxazoles via a Palladium-Catalyzed Decarboxylative Addition/Cyclization Reaction Sequence of Aromatic Carboxylic Acids with Functionalized Aliphatic Nitriles
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We herein report an efficient approach for the assembly of multiply substituted imidazoles and oxazoles in a single-step manner. These transformations are based on a decarboxylation addition and annulation of readily accessible aromatic carboxylic acids a
- Dai, Ling,Yu, Shuling,Lv, Ningning,Ye, Xuanzeng,Shao, Yinlin,Chen, Zhongyan,Chen, Jiuxi
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supporting information
p. 5664 - 5668
(2021/08/01)
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- A High-Throughput Screening Method for the Directed Evolution of Hydroxynitrile Lyase towards Cyanohydrin Synthesis
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Chiral cyanohydrins are useful intermediates in the pharmaceutical and agricultural industries. In nature, hydroxynitrile lyases (HNLs) are a kind of elegant tool for enantioselective hydrocyanation of carbonyl compounds. However, currently available methods for demonstrating hydrocyanation are still stalled at precise, but low-throughput, GC or HPLC analyses. Herein, we report a chromogenic high-throughput screening (HTS) method that is feasible for the cyanohydrin synthesis reaction. This method was highly anti-interference and sensitive, and could be used to directly profile the substrate scope of HNLs either in cell-free extract or fermentation clear broth. This HTS method was also validated by generating new variants of PcHNL5 that presented higher catalytic efficiency and stronger acidic tolerance in variant libraries.
- Zheng, Yu-Cong,Ding, Liang-Yi,Jia, Qiao,Lin, Zuming,Hong, Ran,Yu, Hui-Lei,Xu, Jian-He
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p. 996 - 1000
(2021/01/15)
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- Constructing a triangular metallacycle with salen-Al and its application to a catalytic cyanosilylation reaction
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A triangular metallosalen-based metallacycle was constructed in quantitative yield by the self-assembly of a 180° bis(pyridyl)salen-Al complex and a 60° diplatinum(ii) acceptor in a 1?:?1 stoichiometric ratio. This metallacycle was then successfully used to cyanosilylate a wide range of benzaldehydes with trimethylsilyl cyanide.
- Li, Bo,Li, Yang,Qiu, Huayu,Xu, Jun,Yin, Shouchun,Zhang, Jinjin,Zhang, Pengfei,Zhang, Yueyue
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p. 10399 - 10402
(2021/10/12)
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- Divergent Palladium-Catalyzed Tandem Reaction of Cyanomethyl Benzoates with Arylboronic Acids: Synthesis of Oxazoles and Isocoumarins
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A palladium-catalyzed tandem reaction of cyanomethyl benzoates with arylboronic acids has been achieved. Substitution at the 2-position of cyanomethyl benzoates was found to be crucial for the selective synthesis of oxazoles and isocoumarins. Cyanomethyl
- Chen, Jiuxi,Chen, Zhongyan,Dai, Ling,Shao, Yinlin,Xiong, Wenzhang,Xu, Tong,Yu, Shuling
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supporting information
(2020/04/15)
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- Synthesis of 2,4,5-Trisubstituted Oxazoles via Pd-Catalyzed C-H Addition to Nitriles/Cyclization Sequences
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A practical and flexible intermolecular protocol for the diverse synthesis of trisubstituted oxazole derivatives via a Pd-catalyzed direct C-H addition of electronic-rich heteroarenes to O-acyl cyanohydrins bearing an α-hydrogen/cyclization sequence is described. A wide range of trisubstituted oxazoles can be prepared from readily available starting materials in good to high yields with high efficiency under redox neutral reaction conditions.
- Zhang, Di,Song, Hao,Cheng, Na,Liao, Wei-Wei
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supporting information
p. 2745 - 2749
(2019/04/30)
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- Supported Ionic Liquid-Like Phases (SILLPs) as Immobilised Catalysts for the Multistep and Multicatalytic Continuous Flow Synthesis of Chiral Cyanohydrins
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Supported Ionic Liquid-Like Phases have been found to be efficient organocatalysts for the synthesis of cyanohydrin esters under solvent-free conditions by an “electrophile-nucleophile dual activation” based on hydrogen bond formation. The combination of
- Peris, Edgar,Porcar, Raúl,Burguete, María Isabel,García-Verdugo, Eduardo,Luis, Santiago V.
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p. 1955 - 1962
(2019/03/13)
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- Preparation method and application of a chiral Zr-MOF catalyst
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The invention relates to a preparation method and application of a chiral Zr-MOF catalyst and belongs to the technical field of chiral catalyst preparation. The structural formula of an organic ligandL of the chiral Zr-MOF catalyst is (R)-4,4'-dimethoxyca
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- Homochiral BINAPDA-Zr-MOF for Heterogeneous Asymmetric Cyanosilylation of Aldehydes
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A new homochiral BINAPDA-Zr-MOF was prepared by a new chiral organic linker of (R)-4,4′-(6,6′-dichloro-2,2′-diethoxyl-[1,1′-binaphthalene]-4,4′-diyl)dibenzoic acid (R-L) and ZrCl4 under solvothermal conditions. Its structure was determined by P
- Jin, Fa-Zheng,Zhao, Chen-Chen,Ma, Hui-Chao,Chen, Gong-Jun,Dong, Yu-Bin
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p. 9253 - 9259
(2019/07/08)
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- Catalytic Transfer Hydration of Cyanohydrins to α-Hydroxyamides
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We report the palladium(II)-catalyzed transfer hydration of cyanohydrins to α-hydroxyamides by using carboxamides as water donors. This method enables selective hydration of various aldehyde- and ketone-derived cyanohydrins to afford α-mono- and α,α-disubstituted-α-hydroxyamides, respectively, under mild conditions (50 °C, 10 min). The direct conversion of fenofibrate, a drug bearing a benzophenone moiety, into a functionalized α,α-diaryl-α-hydroxyamide was achieved by means of a hydrocyanation-transfer hydration sequence. Preliminary kinetic studies and the synthesis of a site-specifically 18O-labeled α-hydroxyamide demonstrated the carbonyl oxygen transfer from the carboxamide reagent into the α-hydroxyamide product.
- Kanda, Tomoya,Naraoka, Asuka,Naka, Hiroshi
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p. 825 - 830
(2019/01/14)
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- Iodine-mediated aryl transfer reaction from arylhydrazine hydrochlorides to nitriles
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An iodine-promoted, metal-, base-, and solvent-free cross-coupling reaction was developed for the synthesis of various useful secondary amides via an aryl N-addition reaction of aryl groups to cyano groups. This aryl transfer reaction proceeds with arylhydrazine hydrochlorides serving as the aryl donors. A labelling experiment shows that the N atom in the product comes from the cyano group of the nitriles, which are low in cost. A plausible radical-driven mechanism is also proposed.
- Zhang, Zhiguo,Li, Xiang,Li, Yinghua,Guo, Yan,Zhao, Xunan,Yan, Yan,Sun, Kai,Zhang, Guisheng
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supporting information
p. 3628 - 3635
(2019/05/29)
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- Controlled Exchange of Achiral Linkers with Chiral Linkers in Zr-Based UiO-68 Metal-Organic Framework
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The development of highly robust heterogeneous catalysts for broad asymmetric reactions has always been a subject of interest, but it remains a synthetic challenge. Here we demonstrated that highly stable metal-organic frameworks (MOFs) with potentially acid-labile chiral catalysts can be synthesized via postsynthetic exchange. Through a one- or two-step ligand exchange, a series of asymmetric metallosalen catalysts with the same or different metal centers are incorporated into a Zr-based UiO-68 MOF to form single- and mixed-M(salen) linker crystals, which cannot be accomplished by direct solvothermal synthesis. The resulting MOFs have been characterized by a variety of techniques including single-crystal X-ray diffraction, N2 sorption, CD, and SEM/TEM-EDS mapping. The single-M(salen) linker MOFs are active and efficient catalysts for asymmetric cyanosilylation of aldehydes, ring-opening of epoxides, oxidative kinetic resolution of secondary alcohols, and aminolysis of stilbene oxide, and the mixed-M(salen) linker variants are active for sequential asymmetric alkene epoxidation/epoxide ring-opening reactions. The chiral MOF catalysts are highly enantioselective and completely heterogeneous and recyclable, making them attractive catalysts for eco-friendly synthesis of fine chemicals. This work not only advances UiO-type MOFs as a new platform for heterogeneous asymmetric catalysis in a variety of syntheses but also provides an attractive strategy for designing robust and versatile heterogeneous catalysts.
- Tan, Chunxia,Han, Xing,Li, Zijian,Liu, Yan,Cui, Yong
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supporting information
p. 16229 - 16236
(2018/11/27)
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- Preparation of chitosan-supported urea materials and their application in some organocatalytic procedures
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An efficient and mild procedure was developed for the preparation of three chitosan-supported ureas containing electron-withdrawing groups. These catalysts were characterized and employed as organocatalysts in different transformations, including the enan
- de Gonzalo, Gonzalo,Franconetti, Antonio,Fernández, Rosario,Lassaletta, José M.,Cabrera-Escribano, Francisca
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p. 365 - 374
(2018/07/25)
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- Hydroxynitrile Lyase Isozymes from Prunus communis: Identification, Characterization and Synthetic Applications
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Biocatalysts originating from Badamu (Prunus communis) have been applied to catalyze the asymmetric synthesis of (R)-4-methylsulfanylmandelonitrile, a key building block of thiamphenicol and florfenicol. Here, four hydroxynitrile lyase (HNL) isozymes from Badamu were cloned and heterologously expressed in Pichia pastoris. The biochemical properties and catalytic performances of these isozymes were comprehensively explored to evaluate their efficiency and selectivity in asymmetric synthesis. Among then, PcHNL5 was identified with outstanding activity and enantioselectivity in asymmetric hydrocyanation. Under the optimized mild biphasic reaction conditions, seventeen prochiral aromatic aldehydes were converted to valuable chiral cyanohydrins with good yields (up to 94%) and excellent optical purities (up to >99.9% ee), which provide a facile access to numerous chiral amino alcohols, hypoglycemic agents, angiotension converting enzyme (ACE) inhibitors and β-blockers. This work therefore underlines the importance of discovering the most potent biocatalyst among a group of isozymes for converting unnatural substrates into value-added products. (Figure presented.).
- Zheng, Yu-Cong,Xu, Jian-He,Wang, Hui,Lin, Guo-Qiang,Hong, Ran,Yu, Hui-Lei
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p. 1185 - 1193
(2017/04/13)
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- Multivariate Metal-Organic Frameworks as Multifunctional Heterogeneous Asymmetric Catalysts for Sequential Reactions
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The search for versatile heterogeneous catalysts with multiple active sites for broad asymmetric transformations has long been of great interest, but it remains a formidable synthetic challenge. Here we demonstrate that multivariate metal-organic frameworks (MTV-MOFs) can be used as an excellent platform to engineer heterogeneous catalysts featuring multiple and cooperative active sites. An isostructural series of 2-fold interpenetrated MTV-MOFs that contain up to three different chiral metallosalen catalysts was constructed and used as efficient and recyclable heterogeneous catalysts for a variety of asymmetric sequential alkene epoxidation/epoxide ring-opening reactions. Interpenetration of the frameworks brings metallosalen units adjacent to each other, allowing cooperative activation, which results in improved efficiency and enantioselectivity over the sum of the individual parts. The fact that manipulation of molecular catalysts in MTV-MOFs can control the activities and selectivities would facilitate the design of novel multifunctional materials for enantioselective processes.
- Xia, Qingchun,Li, Zijian,Tan, Chunxia,Liu, Yan,Gong, Wei,Cui, Yong
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supporting information
p. 8259 - 8266
(2017/06/28)
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- The first porphyrin-salen based chiral metal-organic framework for asymmetric cyanosilylation of aldehydes
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The first porphyrin-salen based chiral metal-organic framework (ps-CMOF) constructed by judiciously incorporating metalloporphyrin and metallosalen struts into one MOF structure is reported, which can serve as an effective heterogeneous catalyst for the a
- Li, Jiawei,Ren, Yanwei,Qi, Chaorong,Jiang, Huanfeng
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supporting information
p. 8223 - 8226
(2017/07/24)
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- TBD- or PS-TBD-catalyzed one-pot synthesis of cyanohydrin carbonates and cyanohydrin acetates from carbonyl compounds
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Cyanation reactions of carbonyl compounds with methyl cyanoformate or acetyl cyanide catalyzed by 5 mol % of 1,5,7-triazabicyclo[4,4,0]dec-5-ene (TBD) were examined. Using methyl cyanoformate, the corresponding cyanohydrin carbonates were readily obtained in high yield for aromatic and aliphatic aldehydes and ketones. Similar results were obtained when acetyl cyanide was used as the cyanide source. The polymer-supported catalyst, PS-TBD, also acted as a good catalyst for this reaction. PS-TBD was easily recovered and reused with minimal activity loss.
- Matsukawa, Satoru,Kimura, Junya,Yoshioka, Miki
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supporting information
(2016/08/30)
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- An orthogonal biocatalytic approach for the safe generation and use of HCN in a multistep continuous preparation of chiral O-acetylcyanohydrins
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An enantioselective preparation of O-acetylcyanohydrins has been accomplished by a three-step telescoped continuous process. The modular components enabled an accurate control of two sequential biotransformations, safe handling of an in situ generated hazardous gas, and in-line stabilization of products. This method proved to be advantageous over the batch protocols in terms of reaction time (40 min vs 345 min) and ease of operation, opening up access to reactions which have often been neglected due to safety concerns.
- Brahma, Aischarya,Musio, Biagia,Ismayilova, Uliviya,Nikbin, Nikzad,Kamptmann, Sonja B.,Siegert, Petra,Jeromin, Günter E.,Ley, Steven V.,Pohl, Martina
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p. 262 - 266
(2016/01/20)
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- High-Throughput Preparation of Optically Active Cyanohydrins Mediated by Lipases
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Cyanohydrins are versatile compounds with high applicability in organic synthesis; they are used as starting materials for the synthesis of other chemical targets with high industrial added value. Lipase-mediated kinetic resolution reactions are a promising route for the synthesis of optically active cyanohydrins. These reactions can be carried out through the acylation of cyanohydrins or the deacylation of cyanohydrin esters, with different biocatalysts and under different reaction conditions. Unfortunately, depending on the substrate structure, long reaction times can be required to achieve suitable enantiomeric excesses. In this context, we present a high-throughput protocol for the production of optically active cyanohydrins in continuous-flow mode. The products were obtained with moderate to good enantioselectivity (E values from 8 up to >200) and with productivity values from 2.4 to 8.7 times higher in continuous-flow mode than in batch mode. Moreover, the reaction times were reduced from hours in batch mode to minutes in continuous-flow mode.
- Thomas, Juliana Christina,Aggio, Bruno Bernardi,Marques de Oliveira, Alfredo Ricardo,Piovan, Leandro
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p. 5964 - 5970
(2016/12/26)
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- Dual Lewis Acid/Lewis Base Catalyzed Acylcyanation of Aldehydes: A Mechanistic Study
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A mechanistic investigation, which included a Hammett correlation analysis, evaluation of the effect of variation of catalyst composition, and low-temperature NMR spectroscopy studies, of the Lewis acid-Lewis base catalyzed addition of acetyl cyanide to prochiral aldehydes provides support for a reaction route that involves Lewis base activation of the acyl cyanide with formation of a potent acylating agent and cyanide ion. The cyanide ion adds to the carbonyl group of the Lewis acid activated aldehyde. O-Acylation by the acylated Lewis base to form the final cyanohydrin ester occurs prior to decomplexation from titanium. For less reactive aldehydes, the addition of cyanide is the rate-determining step, whereas, for more reactive, electron-deficient aldehydes, cyanide addition is rapid and reversible and is followed by rate-limiting acylation. The resting state of the catalyst lies outside the catalytic cycle and is believed to be a monomeric titanium complex with two alcoholate ligands, which only slowly converts into the product.
- Laurell Nash, Anna,Hertzberg, Robin,Wen, Ye-Qian,Dahlgren, Bj?rn,Brinck, Tore,Moberg, Christina
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p. 3821 - 3829
(2016/03/08)
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- Chemoenzymatic flow cascade for the synthesis of protected mandelonitrile derivatives
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A chemoenzymatic two-step cascade process, with both steps having incompatible reaction conditions, was successfully performed in continuous flow. The chemoenzymatic aqueous formation of cyanohydrins was integrated with a subsequent organic phase protection step in a single flow process utilising a membrane-based phase separation module. The wider applicability of our setup was demonstrated with the synthesis of nine protected cyanohydrin derivatives, all obtained in good yields and high to excellent enantioselectivity.
- Delville, Marille M. E.,Koch, Kaspar,Van Hest, Jan C. M.,Rutjes, Floris P. J. T.
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p. 1634 - 1638
(2015/03/05)
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- Improving the properties of bacterial r-selective hydroxynitrile lyases for industrial applications
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Hydroxynitrile lyases (HNLs) catalyse the reversible cleavage of cyanohydrins to carbonyl compounds and HCN. The recent discovery of bacterial HNLs with a cupin fold gave rise to a new promising class of these enzymes. They are interesting candidates for the synthesis of cyanohydrins on an industrial scale owing to their high expression levels in Escherichia coli. The activity and enantioselectivity of the manganese-dependent HNL from Granulicella tundricola (GtHNL) were significantly improved by site-saturation mutagenesis of active site amino acids. The combination of beneficial mutations resulted in a variant with 490-fold higher specific activity in comparison to the wild-type enzyme. More importantly, GtHNL-A40H/V42T/Q110H is a highly competitive alternative for the synthesis of chiral cyanohydrins, such as 2-chlorobenzaldehyde cyanohydrin, (R)-2-hydroxy-4-phenylbutyronitrile, and (R)-2-hydroxy-4-phenyl-3-butene nitrile, which serve as intermediates for the synthesis of pharmaceuticals.
- Wiedner, Romana,Kothbauer, Bettina,Pavkov-Keller, Tea,Gruber-Khadjawi, Mandana,Gruber, Karl,Schwab, Helmut,Steiner, Kerstin
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p. 325 - 332
(2015/03/05)
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- Direct and Post-Synthesis Incorporation of Chiral Metallosalen Catalysts into Metal-Organic Frameworks for Asymmetric Organic Transformations
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Two chiral porous metal-organic frameworks (MOFs) were constructed from [VO(salen)]-derived dicarboxylate and dipyridine bridging ligands. After oxidation of VIV to VV, they were found to be highly effective, recyclable, and reusable
- Xi, Weiqin,Liu, Yan,Xia, Qingchun,Li, Zijian,Cui, Yong
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supporting information
p. 12581 - 12585
(2015/09/01)
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- A homochiral metal-organic framework as an effective asymmetric catalyst for cyanohydrin synthesis
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A homochiral metal-organic framework (MOF) of an enantiopure 2,2′-dihydroxy-1,1′-biphenyl ligand was constructed. After exchanging one proton of the dihydroxyl group for Li(I) ions, the framework is shown to be a highly efficient and recyclable heterogene
- Mo, Ke,Yang, Yuhua,Cui, Yong
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p. 1746 - 1749
(2014/03/21)
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- Proline adducts of metallo-organic, sextuply-stranded lanterns as homogeneous catalysts for asymmetric catalysis
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Two homochiral metal-organic, sextuply-stranded, lantern-like complexes, Ce-L-Pro1 and Ce-D-Pro1, were synthesized via self-assembly by incorporating a L or D-pyrrolidine moiety within the respective ligands. The Ce-Pro1 complexes are comprised of chiral pyrrolidine-containing ligands and have lantern-like cavities. They function as asymmetric catalysts that promote cyanosilylation reactions with good conversions and enantioselectivity.
- Zhu, Wenting,Wu, Xiao,He, Cheng,Duan, Chunying
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p. 10477 - 10481
(2013/11/19)
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- A simple separation method for (S)-hydroxynitrile lyase from cassava and its application in asymmetric cyanohydrination
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Using an acetone precipitation method, crude (S)-hydroxynitrile lyase [(S)-MeHNL] was separated from Munihot esculenta (cassava) leaves, and used directly as biocatalyst to catalyze asymmetric cyanohydrination and produce cyanohydrins with enantiomeric purities (≥90% ee) significantly greater than those previously reported. The use of a water/i-Pr2O system with an enzyme, NaCN, and appropriate amounts of acetic acid is crucial in improving the stereoselectivity of cyanohydrin formation by minimizing the non-enzymatic reaction and the racemization of the chiral products. The proposed isolation method for crude (S)-MeHNL has a high value because of its simplicity, and low cost as well as the high activity of the crude (S)-MeHNL.
- Zheng, Zubiao,Zi, Yan,Li, Zhongzhou,Zou, Xinzhuo
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p. 434 - 439
(2013/06/27)
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- One-step preparation of O-(α-bromoacyl) cyanohydrins by minor enantiomer recycling: Synthesis of 4-amino-2(5H)-furanones
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O-(α-Bromoacyl) cyanohydrins were prepared in a single step from a range of different aldehydes in combination with α-bromoacyl cyanides. By the use of a cyclic procedure where the two minor diastereoisomers from a chiral Lewis acid-catalyzed reaction und
- Hertzberg, Robin,Moberg, Christina
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p. 9174 - 9180
(2013/10/08)
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- Asymmetric cyanohydrin synthesis using an aluminium(salan) complex
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The asymmetric addition of trimethylsilyl cyanide to aldehydes catalysed by chiral metal(salan) complexes has been investigated. Salan complexes of titanium and vanadium displayed only low catalytic activity, but a bimetallic aluminium(salan) complex gave
- North, Michael,Stewart, Emma L.,Young, Carl
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p. 1218 - 1225,8
(2020/09/09)
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- Lipase-catalyzed kinetic resolution of (±)-mandelonitrile under conventional condition and microwave irradiation
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The kinetic resolution of (±)-mandelonitrile was carried out using lipase from Candida antarctica under conventional condition (orbital shaker) and microwave irradiation in toluene, producing the (S)-mandelonitrile acetate with high selectivity (up to > 98percent ee, enantiomeric excess). The unreacted (R)-mandelonitrile under microwave irradiation and conventional condition was partially converted into benzaldehyde by spontaneous chemical equilibrium. The (S)-mandelonitrile acetate under microwave irradiation was produced with 92percent ee and 35percent yield for 8 h of reaction. Conventional transesterification of (±)-mandelonitrile in an orbital shaker produced unreacted (R)-mandelonitrile (51percent ee) and (S)-mandelonitrile acetate (98percent ee) in accordance with Kazlauskas rule for 184 h of reaction.
- Ribeiro, Sandra S.,De Oliveira, Julieta R.,Porto, Andre? L. M.
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body text
p. 1395 - 1399
(2012/10/18)
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- Asymmetric induction by helical poly(amino acid)s in cyanosilylation of aldehydes
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It was first demonstrated that helical poly(amino acid)s have an ability to induce enantioselectivity in the cyanosilylation of aldehydes. The helicity of poly(amino acid)s and the N-terminal amino group were essential for the enantioinduction of the reaction.
- Akagawa, Kengo,Kudo, Kazuaki
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supporting information
p. 5981 - 5983,3
(2020/08/20)
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- Cyanative self-condensation of aromatic aldehydes promoted by VO(O iPr)3-Lewis base as a cooperative catalyst
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Self-condensation of aromatic aldehydes with trimethylsilyl cyanide proceeded by the cooperative catalytic effect of VO(OiPr)3 and a Lewis base to give the corresponding O-acylated cyanohydrins. The reaction conversion and selectivity were strongly dependent on the solvent used, the Lewis base, and the presence of oxygen. All the nine kinds of aromatic aldehydes considered herein afforded the O-acylated cyanohydrins with excellent selectivity under an O2 atmosphere.
- Kodama, Koichi,Kawamata, Hiroaki,Takahashi, Naoya,Hirose, Takuji
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p. 9440 - 9446
(2013/01/15)
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- α-Pinene-type chiral Schiff bases as tridentate ligands in asymmetric addition reactions
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A group of tridentate Schiff bases derived from (+)-α-pinene were synthesized. The steric effects in the transition state, the importance of π-π stacking interactions as well as the electronic effects of aryl aldehydes according to Hammett constant values in the enantioselective addition of Et2Zn to aldehydes with the use of Schiff bases as chiral ligands are described. Also, a variety of aldehydes were cyanated using a catalyst prepared in situ from titanium tetraisopropoxide and chiral Schiff bases. The influence of a conjugated double-bond in the cyanation substrates on enantioselectivity was observed. The chemical structures of the chiral Schiff base-titanium alkoxide complexes are discussed based on their 1H and 13C NMR spectra. 3D models of the Zn2-complex catalyst and Ti-complex catalyst containing α-pinane-type Schiff bases based on X-ray diffraction experiments are postulated. The models presented were consistent with the reported chirality of the addition product and observed ee.
- Jaworska, Magdalena,Blocka, Ewelina,Kozakiewicz, Anna,Welniak, Miroslaw
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experimental part
p. 648 - 657
(2011/07/08)
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- N-heterocyclic carbene catalyzed cyanation reaction of carbonyl compounds with ethyl cyanoformate and acetyl cyanide
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N-heterocyclic carbene (NHC) has been employed as an efficient catalyst for cyanation reaction of carbonyl compounds. Under catalysis of 1 mol % NHCs, various aldehydes and 2,2,2-trifluoroacetophenone coupled with ethyl cyanoformate in THF to provide cyanohydrins ethyl carbonates in excellent yields. While in the presence of 10 mol % catalyst, different types of aldehydes and 2,2,2-trifluoroacetophenone reacted with acetyl cyanide in dichloroethane to give acylated cyanohydrins in moderate to high yields.
- Zhang, Jie,Du, Guangfen,Xu, Yueke,He, Lin,Dai, Bin
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supporting information; experimental part
p. 7153 - 7156
(2012/01/05)
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- In situ evaluation of lipase performances through dynamic asymmetric cyanohydrin resolution
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A dynamic resolution process based on multiple reversible cyanohydrin formation coupled to lipase-mediated transesterification is demonstrated. The resulting process resulted in the efficient evaluation of complex lipase performances in asymmetric cyanohydrin acylate synthesis. Dynamic systems were generated and resolved in situ, and the effects of the reaction conditions could be directly monitored for the overall system. By this concept, the enzyme activity, chemo- and stereoselectivity for all involved substrates could be simultaneously evaluated.
- Sakulsombat, Morakot,Vongvilai, Pornrapee,Ramstroem, Olof
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experimental part
p. 1112 - 1117
(2011/04/16)
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- Cooperative thiourea-Bronsted acid organocatalysis: Enantioselective cyanosilylation of aldehydes with TMSCN
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We report a new thiourea - Bronsted acid cooperative catalytic system for the enantioselective cyanosilylation of aldehydes with yields up to 90% and enantioselectivities up to 88%. The addition of an achiral acid was found to be crucial for high asymmetric induction. Mechanistic investigations using a combination of NMR, ESI-MS, and density functional theory computations (including solvent corrections) at the M06/6-31G(d,p) level of theory suggest that the key catalytic species results from the cooperative interaction of bifunctional thioureas and an achiral acid that form well-defined chiral hydrogen-bonding environments.
- Zhang, Zhiguo,Lippert, Katharina M.,Hausmann, Heike,Kotke, Mike,Schreiner, Peter R.
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experimental part
p. 9764 - 9776
(2012/01/03)
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- Probing the enantioselectivity of a diverse group of purified cobalt-centred nitrile hydratases
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In this study a diverse range of purified cobalt containing nitrile hydratases (NHases, EC 4.2.1.84) from Rhodopseudomonas palustris HaA2 (HaA2), Rhodopseudomonas palustris CGA009 (009), Sinorhizobium meliloti 1021 (1021), and Nitriliruptor alkaliphilus (iso2), were screened for the first time for their enantioselectivity towards a broad range of chiral nitriles. Enantiomeric ratios of >100 were found for the NHases from HaA2 and CGA009 on 2-phenylpropionitrile. In contrast, the Fe-containing NHase from the well-characterized Rhodococcus erythropolis AJ270 (AJ270) was practically aselective with a range of different α-phenylacetonitriles. In general, at least one bulky group in close proximity to the α-position of the chiral nitriles seemed to be necessary for enantioselectivity with all NHases tested. Nitrile groups attached to a quaternary carbon atom were only reluctantly accepted and showed no selectivity. Enantiomeric ratios of 80 and >100 for AJ270 and iso2, respectively, were found for the pharmaceutical intermediate naproxennitrile, and 3-(1-cyanoethyl)benzoic acid was hydrated to the corresponding amide by iso2 with an enantiomeric ratio of >100.
- Van Pelt,Zhang,Otten,Holt,Sorokin,Van Rantwijk,Black,Perry,Sheldon
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experimental part
p. 3011 - 3019
(2011/06/17)
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- Enantioselective O-acetylcyanation/cyanoformylation of aldehydes using catalysts with built-in crown ether-like motif in chiral macrocyclic V(V) salen complexes
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Chiral macrocyclic V(V) salen complexes 1a-f derived from macrocyclic ligands obtained by the reaction of 1R,2R-(-) diaminocyclohexane/(1R,2R)-(+)-1, 2-diphenylethylenediamine with bis-aldehydes 2 and 3 were synthesized and used as efficient catalysts in asymmetric cyanation reactions. The V(V) catalysts demonstrated excellent performance (product yields and ees up to 99%) with potassium cyanide (KCN) and sodium cyanide (NaCN). The catalytic system also performed very well with a safer source of cyanide-ethyl cyanoformate to give cyanohydrin carbonates in excellent yield and ee (up to 97%). The V(V) macrocyclic salen complex 1b retained its performance at multi-gram level and was conveniently recycled for a number of times.
- Khan, Noor-Ul H.,Sadhukhan, Arghya,Maity, Nabin C.,Kureshy, Rukhsana I.,Abdi, Sayed H.R.,Saravanan,Bajaj, Hari C.
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experimental part
p. 7073 - 7080
(2011/10/07)
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- Homochiral metal-organic frameworks for heterogeneous asymmetric catalysis
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Homochiral crystallizations of two enantiomeric metal-organic frameworks (MOFs) Ce-MDIP1 and Ce-MDIP2 were achieved by using l- or d-BCIP as chiral inductions, respectively, where the chiralities were characterized by solid state CD spectra. Ce-MDIPs exhibit excellent catalytic activity and high enantioselectivity for the asymmetric cyanosilylation of aromatic aldehydes; the homochiral Cd-TBT MOF having l-PYI as a chiral adduct exhibits stereochemical catalysis toward the Aldol reactions.
- Dang, Dongbin,Wu, Pengyan,He, Cheng,Xie, Zhong,Duan, Chunying
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supporting information; experimental part
p. 14321 - 14323
(2010/12/19)
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- Ionic liquids for enhancing the enantioselectivity of isolated BVMO-catalysed oxidations
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The present study describes the first-time usage of an isolated thermostable Baeyer-Villiger monooxygenase (phenylacetone monooxygenase, PAMO) in the presence of ionic liquids. The stability, activity and selectivity of PAMO as an oxidative enzyme in the presence of different ionic liquids were studied. This revealed that the addition of some specific ionic liquids, such Ammoeng 102 and [bmim]MeSO4, can significantly enhance the E-value in the oxidation of racemic benzylketones. Moreover, the use of ionic liquids increases the optimal substrate concentration for performing Baeyer-Villiger oxidation, thereby extending the biocatalytic repertoire of PAMO for synthetic applications.
- Rodriguez, Cristina,De Gonzalo, Gonzalo,Fraaije, Marco W.,Gotor, Vicente
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scheme or table
p. 2255 - 2260
(2011/02/24)
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- Enzymatic kinetic resolution of racemic cyanohydrins via enantioselective acylation
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Enzymatic kinetic resolution of a series of aromatic and aliphatic cyanohydrins in organic media has been investigated. The behavior of potential lipases, molecular sieves, acyl reagent, reaction temperature, and organic solvents on the kinetic resolution was studied. The influence of substrate structure, steric, and electronic nature and position of the aryl substituent on the enantioselectivity was discussed. Under the optimized reaction conditions, good enantioselectivity could be achieved for most of the investigated compounds. Specifically, substrates 1a, 1c, 1d, 1f, 1u could be resolved with the kinetic enantiomer ratio (E) higher than 200.
- Xu, Qing,Xie, Yongli,Geng, Xiaohong,Chen, Peiran
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experimental part
p. 624 - 630
(2010/09/07)
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- Asymmetric synthesis of a new salen type-titanium complex as the catalyst for asymmetric trimethylsilylcyanation of aldehydes
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This work describes the asymmetric synthesis of a new salen-type ligand via a Diels-Alder reaction and Curtius rearrangement. The ligand with a norbornane skeleton was used in the trimethylsilylcyanation of aldehydes, but the enantioselectivity was 55%ee. The norborane skeleton was cleaved to destroy this rigidity, and the eanatioselectivity was thereby increased to 85%ee.
- Lin, Zheng-Chang,Chen, Chinpiao
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experimental part
p. 726 - 737
(2011/04/23)
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- Investigation of lewis acid versus lewis base catalysis in asymmetric cyanohydrin synthesis
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The asymmetric addition of trimethylsilyl cyanide to aldehydes can be catalysed by Lewis acids and/or Lewis bases, which activate the aldehyde and trimethylsilyl cyanide, respectively. It is not always apparent from the structure of the catalyst whether Lewis acid or Lewis base catalysis predominates. To investigate this in the context of using salen complexes of titanium, vanadium and aluminium as catalysts, a Hammett analysis of asymmetric cyanohydrin synthesis was undertaken. When Lewis acid catalysis is dominant, a significantly positive reaction constant is observed, whereas reactions dominated by Lewis base catalysis give much smaller reaction constants. [{Ti(salen)O}2] was found to show the highest degree of Lewis acid catalysis, whereas two [VO(salen)X] (X = EtOSO3 or NCS) complexes both displayed lower degrees of Lewis acid catalysis. In the case of reactions catalysed by [{Al(salen)}2O] and triphenyl- phosphine oxide, a non-linear Ham- mett plot was observed, which is indicative of a change in mechanism with increasing Lewis base catalysis as the carbonyl compound becomes more electron-deficient. These results suggested that the aluminium complex/tri- phenylphosphine oxide catalyst system should also catalyse the asymmetric addition of trimethylsilyl cyanide to ke- tones and this was found to be the case.
- North, Michael,Omedes-Pujol, Marta,Williamson, Courtney
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experimental part
p. 11367 - 11375
(2010/11/17)
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- Kinetics and mechanism of vanadium catalysed asymmetric cyanohydrin synthesis in propylene carbonate
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Propylene carbonate can be used as a green solvent for the asymmetric synthesis of cyanohydrin trimethylsilyl ethers from aldehydes and trimethylsilyl cyanide catalysed by VO(salen)NCS, though reactions are slower in this solvent than the corresponding re
- North, Michael,Omedes-Pujol, Marta
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experimental part
p. 1043 - 1055
(2011/03/22)
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- Asymmetric cyanohydrin formation from aldehydes catalyzed by manganese Schiff base complexes
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The catalyst generated in situ from Mn(OAc)2 and a chiral Schiff base ligand exhibited excellent catalytic abilities in asymmetric cyanohydrin formation from aldehydes with sodium cyanide in up to 99% enantioselectivity and good yield.
- Qu, Yanyang,Jing, Linhai,Wu, Zhiqing,Wu, Di,Zhou, Xiangge
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experimental part
p. 187 - 190
(2010/04/28)
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- ZnI2-catalyzed cyanation of acyl chlorides with TMS-CN: An interesting role of iodine
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Both aliphatic and aromatic acyl cyanides have been synthesized with TMSCN and acyl chloride with ZnI2 (0.5 mol%). However the in situ generated I2 is proposed accounting for the formation of by-product O-TMS enolate at high catalyst loading rather than 0.5 mol%. Asymmetric reduction of benzoyl cyanide with borane has been explored in 82% yield and 24% ee.
- Zeng, Wei,Yang, Jingya,Meng, Bo,Zhang, Bo,Jiang, Mingzhe,Chen, Fu-Xue
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body text
p. 637 - 641
(2010/06/15)
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- Minor enantiomer recycling: Metal catalyst, organocatalyst and biocatalyst working in concert
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A minor enantiomer recycling one-pot procedure employing two reinforcing chiral catalysts has been developed. Continuous regeneration of the achiral starting material is effected via selective enzyme-catalyzed hydrolysis of the minor product enantiomer fr
- Wingstrand, Erica,Laurell, Anna,Fransson, Linda,Hult, Karl,Moberg, Christina
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supporting information; experimental part
p. 12107 - 12113
(2010/08/03)
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- A bimetallic aluminium(salen) complex for asymmetric cyanohydrin synthesis
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In the presence of a phosphine oxide cocatalyst, a bimetallic aluminium(salen) complex was found to catalyse the asymmetric addition of trimethylsilyl cyanide to aldehydes. Under optimised conditions, enantioselectivities of 53-96% were obtained using 2 m
- North, Michael,Williamson, Courtney
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experimental part
p. 3249 - 3252
(2009/08/17)
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- Ionic liquid [bmim]BF4 as an efficient and recyclable reaction medium for the synthesis of O-acetyl cyanohydrin via one-pot condensation of aldehyde, TMSCN, and Ac2O
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Ionic liquid [bmim]BF4 has been demonstrated to be an efficient and environmentally friendly reaction medium as well as reaction promoter for the synthesis of O-acetyl cyanohydrin via one-pot condensation of aldehyde, TMSCN, and Ac2O without Lewis acid or
- Shen, Zhi-Liang,Ji, Shun-Jun
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experimental part
p. 808 - 818
(2009/08/08)
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- One-pot three components synthesis of O-acetylcyanohydrins with TMSCN, acetic anhydride and carbonyl compounds under solvent-free condition
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One-pot three components synthesis of O-acetylcyanohydrins has been developed in the presence of B(C6F5)3 as the catalyst. Variety of aldehydes or ketones reacts with TMSCN and acetic anhydride (Ac2O) under the
- Kadam, Santosh T.,Kim, Sung Soo
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experimental part
p. 6330 - 6334
(2010/01/06)
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