- Synthesis of a new chiral cyclic o-hydroxynaphthylphosphonodiamide and its application as ligand catalyst in asymmetric silylcyanation of aromatic aldehydes
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A new chiral cyclic o-hydroxynaphthylphosphonodiamide (+)-2 was synthesized starting from (+)-cis-1,2,2-trimethylcyclopentane-1,3-diamine. The absolute configuration of phosphorus atom was determined as S by X-ray diffraction analysis. Excellent enantiose
- He, Ke,Zhou, Zhenghong,Wang, Lixin,Li, Kangying,Zhao, Guofeng,Zhou, Qilin,Tang, Chuchi
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- CO2-Enabled Cyanohydrin Synthesis and Facile Iterative Homologation Reactions**
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Thermodynamic and kinetic control of a chemical process is the key to access desired products and states. Changes are made when a desired product is not accessible; one may manipulate the reaction with additional reagents, catalysts and/or protecting groups. Here we report the use of carbon dioxide to accelerate cyanohydrin synthesis under neutral conditions with an insoluble cyanide source (KCN) without generating toxic HCN. Under inert atmosphere, the reaction is essentially not operative due to the unfavored equilibrium. The utility of CO2-mediated selective cyanohydrin synthesis was further showcased by broadening Kiliani–Fischer synthesis under neutral conditions. This protocol offers an easy access to a variety of polyols, cyanohydrins, linear alkylnitriles, by simply starting from alkyl- and arylaldehydes, KCN and an atmospheric pressure of CO2.
- Juhl, Martin,Petersen, Allan R.,Lee, Ji-Woong
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supporting information
p. 228 - 232
(2020/11/30)
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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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- Highly chemoselective and efficient Strecker reaction of aldehydes with TMSCN catalyzed by MgI2 etherate under solvent-free conditions
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Strecker reaction of various substituted aromatic aldehydes, heteroaromatic aldehydes, aliphatic aldehydes and α,β-unsaturated aldehydes with trimethylsilyl cyanide (TMSCN) was realized in the presence of 5 mol % of MgI2 etherate in a mild, efficient and highly chemoselective manner under solvent-free conditions.
- He, Kailun,Liu, Huijun,Zhang, Xingxian,Zhou, Jing
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supporting information
p. 933 - 936
(2019/03/08)
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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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- Acceptorless and Base-free Dehydrogenation of Cyanohydrin with (η6-Arene)halide(Bidentate Phosphine)ruthenium(II) Complex
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Ruthenium-catalyzed dehydrogenation of cyanohydrins under acceptorless and base-free conditions was demonstrated for the first time in the synthesis of acyl cyanide. As opposed to the thermodynamically preferred elimination of hydrogen cyanide, the dehydrogenation of cyanohydrins could be kinetically controlled with ruthenium (II) bidentate phosphine complexes. The effects of the arene, phosphine ligands and counter anions were investigated in regard to catalytic activity and selectivity. Selective dehydrogenation can occur via β-hydride elimination with the experimentally observed [(alkoxide)Ru] complex. (Figure presented.).
- Kim, Kicheol,Moeljadi, Adhitya Mangala Putra,Hirao, Hajime,Hong, Soon Hyeok
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supporting information
p. 3292 - 3298
(2017/09/06)
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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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- 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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- Enantioselective cyanosilylation of aldehydes catalyzed by a multistereogenic salen-Mn(III) complex with a rotatable benzylic group as a helping hand
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A multistereogenic salen-Mn(iii) complex bearing an aromatic pocket and two benzylic groups as helping hands was found to be efficient in the catalysis of asymmetric cyanosilylation. The salen-Mn catalyst partially mimics the functions of biocatalysts by
- Wei, Yun-Long,Huang, Wei-Sheng,Cui, Yu-Ming,Yang, Ke-Fang,Xu, Zheng,Xu, Li-Wen
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p. 3098 - 3103
(2015/02/02)
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- Solid phase behavior in the chiral systems of various 2-hydroxy-2-phenylacetic acid (mandelic acid) derivatives
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The solid phase behavior of a series of monosubstituted F-, Cl-, Br-, I-, and CH3- and two 2,4-halogen-disubstituted 2-hydroxy-2-phenylacetic acid (mandelic acid) derivatives was investigated. The study includes detailed information about melting temperature, melting enthalpy, X-ray diffraction data, as well as selected binary phase diagrams of the respective chiral systems. Aside from the known metastable conglomerate 2-chloromandelic acid, evidence for two more metastable conglomerates was found.
- Von Langermann, Jan,Temmel, Erik,Seidel-Morgenstern, Andreas,Lorenz, Heike
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p. 721 - 728
(2015/03/30)
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- P(NMe2)3-Mediated Umpolung Alkylation and Nonylidic Olefination of α-Keto Esters
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A commercial phosphorus-based reagent (P(NMe2)3) mediates umpolung alkylation of methyl aroylformates with benzylic and allylic bromides, leading to either Barbier-type addition or ylide-free olefination products upon workup. The reaction sequence is initiated by a two-electron redox addition of the tricoordinate phosphorus reagent with an α-keto ester compound (Kukhtin-Ramirez addition). A mechanistic rationale is offered for the chemoselectivity upon which the success of this nonmetal mediated C-C bond forming strategy is based.
- Wang, Sunewang Rixin,Radosevich, Alexander T.
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supporting information
p. 3810 - 3813
(2015/08/18)
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- A magnetic nanoparticle catalyzed eco-friendly synthesis of cyanohydrins in a deep eutectic solvent
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Magnetic Fe3O4 nanoparticles in deep eutectic solvents (DESs) have been regard as excellent catalysts for highly efficient cyanosilylation of various aldehydes and epoxides using trimethylsilyl cyanide TMSCN in high yields with excellent selectivity. Fe3O4 nanoparticles were synthesized and applied as a catalyst for the preparation of a wide variety of cyanohydrins (α-hydroxy nitriles and β-hydroxy nitriles) in readily available urea-choline chloride deep eutectic solvent DES as the most promising environmentally benign and cost-effective green solvent. Magnetic DES operates at very mild reaction conditions and can be easily recycled without significant loss of its catalytic activity.
- Azizi, Najmedin,Rahimi, Zahra,Alipour, Masoumeh
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p. 61191 - 61198
(2015/07/28)
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- Enantioselective cyanosilylation of aldehydes catalyzed by novel camphor derived Schiff bases-titanium(IV) complexes
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Five tridentate Schiff bases have been prepared from (1R,2S,3R,4S)-3-amino- 1,7,7-trimethylbicyclo[2.2.1]heptan-2-ol and salicylaldehydes. X-ray structure investigation revealed differences in their molecular conformation, and their titanium(IV) complexes
- B?ocka, Ewelina,Bosiak, Mariusz J.,We?niak, Miros?aw,Ludwiczak, Agnieszka,Wojtczak, Andrzej
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p. 554 - 562
(2014/05/06)
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- Kinetic resolution of mandelate esters via stereoselective acylation catalyzed by lipase PS-30
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By using lipase PS-30 as catalyst, the kinetic resolution of a series of racemic mandelate esters has been achieved via stereoselective acylation. The value of kinetic enantiomeric ratio (E) reached up to 197.5. Substituent effect is briefly discussed.
- Chen, Peiran,Yang, Wenhong
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supporting information
p. 2290 - 2294
(2014/04/17)
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- Relationships between the racemic structures of substituted mandelic acids containing 8- and 10-membered hydrogen bonded dimer rings
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The structures of 27 monosubstituted mandelic acids, including several of their polymorphs, plus unsubstituted mandelic acid itself (two polymorphs) are investigated for structural similarity. The results, presented pictorially as a structural relationship plot, show that rather more structures are built up from the carboxyl-chain hydroxyl hydrogen bonded dimer than from the conventional carboxylic acid dimer. The results show how all the structures are related and, based on the two types of dimer, the degree of similarity that they possess. Some structures with Z′ > 1 contain both sorts of dimers and there are many examples of isostructural sets within the structures so far determined. We also present an example where analysing similarity in related families of structures highlights a structure that should be present and which has indeed then proceeded to be synthesised and determined.
- Coles,Ellis,Leung,Sarson,Threlfall,Tizzard
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p. 10816 - 10823
(2015/02/19)
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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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- NaCN/DOWEX(R)50WX4: A convenient system for synthesis of cyanohydrins from aldehydes
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A variety of cyanohydrins were prepared from Aldehydes with sodium cyanide and DOWEX(R)50WX4 in a convenient procedure.
- Sofighaderi, Sargol,Setamdideh, Davood
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p. 1135 - 1137
(2014/03/21)
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- The preparation of various new heterocyclic compounds via cyclization of substituted derivatives of phenacyl esters of hydrazonoacetic acid
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A procedure for the preparation of derivatives of phenacyl hydrazonopropanoates and their application in the synthesis of various heterocycles has been developed. Not only is the preparation of indole derivatives described, but also a new method for the preparation of previously unknown pyridazine derivatives.
- Melnicky, Radek,Grepl, Martin,Lycka, Antonin,Bertolasi, Valerio,Kvapil, Lubomir,Dvorakova, Barbora,Hradil, Pavel
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p. 2447 - 2457
(2013/09/23)
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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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- An efficient cyanosilylation of aldehydes with trimethylsilyl cyanide catalysed by MgI2 etherate
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A convenient procedure for the synthesis of cyanohydrins by the addition of trimethylsilyl cyanide to aromatic aldehydes, heteroaromatic aldehydes, aliphatic aldehydes and unsaturated aldehydes catalysed by MgI2 etherate (MgI2(OEt2)n) in good to excellent yields is described.
- Wang, Yanping,Feng, Meiling,Liu, Yingshuai,Zhang, Xingxian
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p. 566 - 567,2
(2020/09/16)
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- Redox-neutral α-cyanation of amines
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α-Aminonitriles inaccessible by traditional Strecker chemistry are obtained in redox-neutral fashion by direct amine α-cyanation/N-alkylation or alternatively, α-aminonitrile isomerization. These unprecedented transformations are catalyzed by simple carboxylic acids.
- Ma, Longle,Chen, Weijie,Seidel, Daniel
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supporting information
p. 15305 - 15308
(2012/10/29)
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- Unsymmetric salen ligands bearing a Lewis base: Intramolecularly cooperative catalysis for cyanosilylation of aldehydes
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A series of unsymmetric salen ligands derived from 1,2-diaminocyclohexane bearing an appended Lewis base on the three-position of one aromatic ring were synthesized by the reaction of various functional salicyaldehydes with the condensation product of 1,2-diaminocyclohexane mono(hydrogen chloride) and 3,5-di-tert-butylsalicylaldehyde. These ligands in conjunction with Ti(O iPr)4 exhibited excellent activity in catalyzing the cyanosilylation of aldehydes with trimethylsilyl cyanide (TMSCN) at mild conditions. The highest activity was observed in the catalyst system with regard to the salen ligand bearing a diethylamino group, which proved to be active even at a high [aldehyde]/[catalyst] ratio up to 50000. In a low catalyst loading of 0.05 mol%, the quantitative conversion of benzaldehyde to the corresponding cyanosilylation product was found within 10 min. at ambient temperature. An intramolecularly cooperative catalysis was proposed wherein the central metal Ti(iv) is suggested to play a role of Lewis acid to activate aldehydes while the appended Lewis base to activate TMSCN.
- Wen, Ye-Qian,Ren, Wei-Min,Lu, Xiao-Bing
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supporting information; experimental part
p. 6323 - 6330
(2011/10/09)
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- Highly active bifunctional salenTi(IV) catalysts for asymmetric cyanosilylation of aldehydes and TMSCN
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A novel enantiopure salen ligand bearing a diphenylphosphine oxide on the 3-position of one aromatic ring was synthesized and combined with Ti(Oi-Pr) 4 as a monometallic bifunctional catalyst for asymmetric cyanosilylation reaction of aldehydes with trimethylsilyl cyanide (TMSCN). The catalyst system exhibited excellent activity and moderate enantioselectivity. The addition of TMSCN to 4-nitrobenzaldehyde in the presence of 1 mol% catalyst loading could complete within 10 min at ambient temperature. An intramolecularly cooperative catalysis was observed in this system wherein the central metal Ti(IV) is suggested to play a role of Lewis acid to activate aldehydes while the appended diphenylphosphine oxide worked as Lewis base to activate TMSCN.
- Wen, Ye Qian,Ren, Wei Min,Lu, Xiao Bing
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scheme or table
p. 1285 - 1288
(2012/01/17)
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- Enantioselective silylcyanation of aldehydes catalyzed by new chiral oxovanadium complex
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Oxovanadium(V) complex 4 was prepared from VOSO4 and tridentate Schiff base ligand, which was prepared from substituted salicylaldehyde and inexpensive (S)-valine. Asymmetric silylcyanation of the aldehydes catalyzed by catalyst 4 afforded cyanohydrins with good enantioselectivities.
- Chu, Chang-Ying,Hsu, Chu-Tin,Lo, Po Hsiang,Uang, Biing-Jiun
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scheme or table
p. 1981 - 1984
(2012/03/10)
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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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p. 9764 - 9776
(2012/01/03)
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- Two-dimensional rhombus grid coordination polymer showing heterogeneous catalytic activities
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A coordination polymer, {[Cd(L)2(DMF)2] ·(ClO4)2·(2DMF)}n (1) (L = bis-(4-imidazol-1-yl-phenyl)-diazene) has been synthesized at room temperature. The polymer forms a two-dimensional (2D) rhombus-grid sheet structure. These 2D sheets are stacked in ABAB... mode with an inter-planar spacing of 3.729 . Each Cd(II) ion is equatorially bonded to four imidazole N atoms belong to four different ligand units while O atoms from two DMF molecules occupy the axial sites. Two ClO4- counter anions as well as two DMF molecules occupy the void space in each rhombus grid. This compound catalyzes cyanosilylation reactions of aromatic aldehydes in dichloromethane under mild conditions in heterogeneous fashion. On heating 1 at 120 °C for 4 h, all DMF molecules are lost and the ClO4- anions move out of the void space to occupy the axial sites on the metal to yield, de-solvated {[Cd(L)2(ClO4)2]}n (1) without losing crystallinity. De-solvated 1 exhibits heterogeneous catalytic activity in several Knoevenagel condensation reactions at RT.
- Sharma, Manish K.,Singh, Prabal P.,Bharadwaj, Parimal K.
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experimental part
p. 6 - 10
(2011/07/30)
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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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- 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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- Chiral linear polymers bonded alternatively with salen and 1,4-dialkoxybenzene: Synthesis and application for Ti-catalyzed asymmetric TMSCN addition to aldehydes
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The synthesis of chiral linear polymers 1a-b having salen and 1,4-dioctyloxybenzene as alternate segments has been accomplished. The GPC analysis showed the molecular weights corresponding to ca. 15 (Mw = 10,999, Mn = 9165 and PDI = 1.20) repeating units for 1a and ca. 8 (Mw = 8547, Mn = 7883 and PDI = 1.08) repeating units for 1b. Polymers 1a-b have been studied with Ti(OiPr)4 as a recyclable catalyst for the asymmetric addition of TMSCN to aldehydes while the selectivity of the polymer catalyst is identical to that of the monomer. The reactions are efficient affording the cyanohydrins with up to 88% ee. The selectivity of the polymer based catalyst 9a is found to be the same to that of the monomer 10a. The reaction provides the advantages of simplified product isolation and easy recovery and recyclability of polymer catalyst 9a without any loss of activity or selectivity.
- Sakthivel, Sekarpandi,Punniyamurthy, Tharmalingam
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experimental part
p. 2834 - 2840
(2011/03/19)
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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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- Chiral solvating agents for cyanohydrins and carboxylic acids
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We have shown that a structure as simple as an ion pair of (R)- or (S)-mandelate and dimethylamminopyridinium ions possesses structural features that are sufficient for NMR enantiodiscrimination of cyanohydrins. Moreover, 1H NMR data of cyanohydrins of known configuration obtained in the presence of the mandelate-dimethylaminopyridinium ion pair point to the existence of a correlation between chemical shifts and absolute configuration of cyanohydrins. Mandelate-DMAPH+ ion pair and mandelonitrile form a 1:1 complex with an association constant of 338 M-1 (ΔG 0, -3.4 kcal/mol) for the (R)-mandelonitrile/(R)-mandelate-DMAPH + and 139 M-1 (ΔG0, -2.9 kcal/mol) for the (R)-mandelonitrile/(S)-mandelate-DMAPH+ complex. To understand the origin of enantiodiscrimination, the geometry optimization and energy minimization of the models of ternary complexes of (S)-mandelonitrile/(R)- mandelate/DMAPH+ and (S)-mandelonitrile/(S)-mandelate/DMAPH + complexes was performed using DFT methodology (B3LYP) with the 6-31+G(d) basis set in Gaussian 3.0. Further, analysis of optimized molecular model obtained from theoretical studies suggested that (i) DMAP may be replaced with other amines, (ii) the hydroxyl group of mandelic acid is not necessary for stabilization of ternary complex and may be replaced with other groups such as methyl, (iii) the ion pair should form a stable ternary complex with any hydrogen-bond donor, provided its OH bond is sufficiently polarized, and (iv) α-H of racemic mandelic acid should also get resolved with optically pure mandelonitrile. These inferences were experimentally verified, which not only validated the proposed model but also led to development of a new chiral solvating agent for determination of ee of carboxylic acids and absolute configuration of aryl but not alkyl carboxylic acids.
- Moon, Lomary S.,Pal, Mohan,Kasetti, Yoganjaneyulu,Bharatam, Prasad V.,Jolly, Ravinder S.
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body text
p. 5487 - 5498
(2010/11/05)
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- A novel chiral (salen)AlIII complex catalyzed asymmetric cyanosilylation of aldehydes
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A novel chiral (salen)AlIII complex was synthesized through the reaction of Et2AlCl and salen (R,R)-1 derived from (R,R)-11,12-diamino-9,10-dihydro-9,10-ethanoanthracene. This complex is an efficient catalyst for the asymmetric trimethylsilylcyanation of aldehydes in the presence of tributylphosphane oxide as an additive. The use of 1 mol-% of the complex led to the corresponding cyanohydrins in high yields (85-94%) with good-to-excellent enantioselectivities (42-92%ee). Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Zeng, Zebing,Zhao, Guofeng,Zhou, Zhenghong,Tang, Chuchi
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experimental part
p. 1615 - 1618
(2009/04/11)
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- Lipase-catalyzed dynamic kinetic resolution giving optically active cyanohydrins: use of silica-supported ammonium hydroxide and porous ceramic-immobilized lipase
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Synthetically useful cyanohydrin acetates, ArCH(OAc)CN (Ar=C6H5, 3,4-methylenedioxyphenyl, 4-Me-C6H4, 4-Cl-C6H4, 4-F-C6H4, 4-CF3-C6H4), were successfully synthesized in high enantiomeric purities (79-93% ee) via the lipase-catalyzed dynamic kinetic resolution (DKR) of cyanohydrins synthesized in situ from the corresponding aldehydes and acetone cyanohydrin. The combined use of silica-supported BTAH (benzyltrimethylammonium hydroxide) and porous ceramic-immobilized lipase under the optimized reaction conditions enabled the remarkable acceleration of the enantioselective DKR reactions.
- Sakai, Takashi,Wang, Kefei,Ema, Tadashi
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p. 2178 - 2183
(2008/09/18)
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- Kinetic resolution of cyanohydrins via enantioselective acylation catalyzed by lipase PS-30
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By using lipase PS-30 as catalyst, the kinetic resolution of a series of racemic cyanohydrins has been achieved via enantioselective acylation. The values of kinetic enantiomeric ratio (E) reached up to 314. Substituent effect is also briefly discussed.
- Xu, Qing,Geng, Xiaohong,Chen, Peiran
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scheme or table
p. 6440 - 6441
(2009/04/06)
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- A new strategy for designing non-C2-symmetric monometallic bifunctional catalysts and their application in enantioselective cyanation of aldehydes
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A monometallic bifunctional catalyst, in which only one imidazolyl moiety is directly attached at the 3-position of a binaphthol moiety, has been developed. The ligand (R)-1, which lacks C2-symmetry and flexible linkers, in combination with Ti(OiPr)4, has been demonstrated to promote the enantioselective cyanation of aldehydes with trimethylsilylcyanide (TMSCN), giving excellent enantioselectivities of up to 98 % ee and high yields of up to 99%. The use of this bifunctional catalytic system obviates the need for additives and is extremely simple as the reagents are added in one portion at the beginning of the reaction. The protocol has been found to tolerate a relatively wide range of aldehydes when 10 mol% of the (R)-1/Ti(OiPr) 4 complex is deployed in CH2Cl2 at -40°C, the conditions which proved most practical and effective. The asymmetric cyanations also proceeded with lower catalyst loadings (5 mol%, or even 2 mol%), still giving satisfactory enantiomeric excesses and yields. Interestingly, the use of freshly distilled TMSCN dried over CaH2 gave a low enantioselectivity and only a moderate yield of the adduct as compared with direct use of the commercial reagent. The results of 13C NMR spectroscopic studies implicate HCN as the actual reactive nucleophile.
- Yang, Fei,Wei, Siping,Chen, Chien-An,Xi, Peihua,Yang, Li,Lan, Jingbo,Gau, Han-Mou,You, Jingsong
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supporting information; experimental part
p. 2223 - 2231
(2009/04/06)
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- Cyanosilylation of aldehydes and ketones catalyzed by nanocrystalline magnesium oxide
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Cyanosilylation of various aldehydes and ketones with TMSCN proceeded smoothly under mild conditions to give the corresponding cyanohydrin trimethylsilyl ethers in the presence of nanocrystalline magnesium oxide. The cyanohydrin trimethylsilyl ethers of aldehydes produced cyanohydrins in good to high yields on treatment with 2 N HCl. 29Si NMR spectral evidence proved that the reaction proceeds through the hypervalent silicate species by coordination to O2-/O- (Lewis basic site) of nanocrystalline magnesium oxide. Copyright Taylor & Francis Group, LLC.
- Lakshmi Kantam,Mahendar, Koosam,Sreedhar, Bojja,Vijay Kumar,Choudary
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experimental part
p. 3919 - 3936
(2009/04/11)
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- Enantioselective cyanosilylation of aldehydes catalyzed by a novel N,N′-dioxide-Ti(OiPr)4 bifunctional catalyst
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A novel bifunctional asymmetric catalyst containing N-oxide and titanium(IV) was developed and applied to the asymmetric cyanosilylation of aldehydes. Optically active trimethylsilyl cyanohydrin ethers were obtained up to 99% yield and 80% ee in the presence of 5 mol % catalyst loading at -78 °C. Based on the experimental results, the catalytic cycle was proposed as a pathway in which Lewis acid and Lewis base activated aldehyde and trimethylsilylcyanide (TMSCN), respectively.
- Zeng, Baiqing,Zhou, Xin,Liu, Xiaohua,Feng, Xiaoming
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p. 5129 - 5136
(2008/02/01)
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- Salicylaldehyde Schiff bases derived from 2-ferrocenyl-2-amino alcohols. Part 1: New chiral ligands for the titanium-catalyzed enantioselective cyanation of aldehydes
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The condensation of a set of diversely substituted (S)-2-amino-2-ferrocenyl ethanol derivatives 1a-e with the salicylaldehydes 5A-C resulted in the generation of a small library of new chiral Schiff base-ligands, whose titanium isopropoxide complexes have
- Ma Moreno, Rosa,Rosol, Malgorzata,Moyano, Albert
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p. 1089 - 1103
(2007/10/03)
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- Asymmetric addition of trimethylsilyl cyanide to aldehydes promoted by chiral polymeric vanadium(V) salen complex as an efficient and recyclable catalyst
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The asymmetric addition of trimethylsilyl cyanide to various aldehydes catalyzed by efficient new vanadyl polymeric salen complexes having 12 repeating salen units was investigated at room temperature. An excellent yield of the trimethylsilylether of cyanohydrins (up to 98%) with high chiral induction (96%) in case of 2-methylbenzaldehyde was achieved in 18 h. The catalyst recovered four times with retention of its performance.
- Khan, Noor-ul H.,Agrawal, Santosh,Kureshy, Rukhsana I.,Abdi, Sayed H.R.,Mayani, Vishal J.,Jasra, Raksh V.
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p. 2659 - 2666
(2007/10/03)
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- Synthesis of the bifunctional BINOL ligands and their applications in the asymmetric additions to carbonyl compounds
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Efficient one-step syntheses of the bifunctional BINOL and H8BINOL ligands (S)-6 and (S)-8 have been developed from the reaction of BINOL and H8BINOL with morpholinomethanol, respectively. The X-ray analyses of these compounds have revealed their structural similarity and difference. The bifunctional H8BINOL (S)-8 is found to be highly enantioselective for the reaction of diphenylzinc with many aliphatic and aromatic aldehydes and especially is the most enantioselective catalyst for linear aliphatic aldehydes. Unlike other catalysts developed for the diphenylzinc addition which often require the addition of a significant amount of diethylzinc with cooling (or heating) the reaction mixture in order to achieve high enantioselectivity, using (S)-8 needs no additive and gives excellent results at room temperature. (S)-8 in combination with diethylzinc and Ti(OiPr)4 can catalyze the highly enantioselective phenylacetylene addition to aromatic aldehydes. It can also promote the phenylacetylene addition to acetophenone at room temperature though the enantioselectivity is not very high yet. Without using Ti(OiPr)4 and a Lewis base additive, (S)-8 in combination with diethylzinc can catalyze the reaction of methyl propiolate with an aldehyde to form the highly functional γ-hydroxy-α,β-acetylenic esters except that the enantioselectivity is low at this stage. The bifunctional BINOL ligand (S)-6 in combination with Me2AlCl is found to be a highly enantioselective catalyst for the addition of TMSCN to both aromatic and aliphatic aldehydes.
- Qin, Ying-Chuan,Liu, Lan,Sabat, Michal,Pu, Lin
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p. 9335 - 9348
(2007/10/03)
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- Chiral Pt(II)/Pd(II) pincer complexes that show C-H?Cl hydrogen bonding: Synthesis and applications to catalytic asymmetric aldol and silylcyanation reactions
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A chiral C2-symmetric NCN ligand, (5R,7R)-1,3-bis(6,6-dimethyl-5,6,7,8-tetrahydro-5,7-methanoquinolin-2-yl)benzene has been synthesized. A direct cyclometalation of this ligand with K2MCl4 (M = Pt, Pd) in dry acetic acid offered the corresponding pincer complexes, [(5R,7R)-1,3-bis(6,6-dimethyl-5,6,7,8-tetrahydro-5,7-methanoquinolin-2-yl)phenyl]platinum(II) chloride 5a and its palladium(II) analogue 5b. The Pt(II) and Pd(II) complexes 5 were characterized by NMR spectroscopy, and X-ray crystal structure analysis was done for the Pt(II) complex. The NMR data for both the complexes and X-ray crystal structural data for the chloro-Pt(II) complex indicate the existence of intramolecular C-H?Cl hydrogen bonding both in solution and in solid states. Chloride abstraction from 5a by treatment with silver triflate resulted in the corresponding triflate complex 6a, which generates the corresponding cationic aqua complex 7a in the presence of water molecules. The Pt(II) complex 6a/7a was used as asymmetric catalyst in the aldol reaction between methyl isocyanoacetate and aldehydes and also in the silylcyanation of aldehydes.
- Yoon, Myeong Sik,Ramesh, Rengan,Kim, Jeongryul,Ryu, Dowook,Ahn, Kyo Han
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p. 5939 - 5946
(2007/10/03)
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- 1,3-DISUBSTITUTED HETEROARYL NMDA/NR2B ANTAGONISTS
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Compounds represented by Formula I: (wherein A, B, D, P, Q, R1, R2, R3, W and Y are described herein) or pharmaceutically acceptable salts thereof, are effective as NMDA/NR2B antagonists useful for treating neurological co
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Page/Page column 65-66
(2010/10/20)
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- A new (R)-hydroxynitrile lyase from Prunus mume: Asymmetric synthesis of cyanohydrins
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A new hydroxynitrile lyase (HNL) was isolated from the seed of Japanese apricot (Prunus mume). The enzyme has similar properties with HNL isolated from other Prunus species and is FAD containing enzyme. It accepts a large number of unnatural substrates (benzaldehyde and its variant) for the addition of HCN to produce the corresponding cyanohydrins in excellent optical and chemical yields. A new HPLC based enantioselective assay technique was developed for the enzyme, which promotes the addition of KCN to benzaldehyde in a buffered solution (pH=4.5).
- Nanda, Samik,Kato, Yasuo,Asano, Yasuhisa
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p. 10908 - 10916
(2007/10/03)
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- Asymmetric cyanohydrin synthesis catalyzed by Al(salen)/triphenylphosphane oxide
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Various aldehydes undergo asymmetric trimethylsilylcyanation with (CH 3)3SiCN (TMSCN) in the presence of a chiral Al(salen) complex and Ph3PO as the catalyst. This is a double activation where Al(salen) plays the role of Lewis acd and POPh3 acts as a Lewis base. Various kind of aldehydes were subjected to the enantioselective addition of (CH3)3SiCN at temperatures between -40 °C and -50 °C. Hydrolysis of the adducts gave cyanohydrins with over 90 % yield and 80 % ee in most cases. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.
- Kim, Sung Soo,Song, Dae Ho
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p. 1777 - 1780
(2007/10/03)
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- A C2-symmetric chiral bipyridyldiol-titanium complex as a catalyst for the asymmetric trimethylsilylcyanation of substituted benzaldehydes
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This article describes a novel C2-symmetric ligand that comprises a central bipyridine-pinene-derived core and two functionalized two diphenylmethanol subunits. The [8′-(hydroxy-diphenyl-methyl)-10,10, 10′,10′-tetramethyl-[5,5′]bi[6-aza-tricyclo[7.1.1.0 2,7]undecyl]-2(7),3,5,2′(7′),3′, 5′-hexane-8-yl]-diphenyl-methanol 1 is an effective catalyst in the enantioselective addition of trimethylsilylcyanide to various aromatic aldehydes with asymmetric inductions of up to 98% ee. Importantly, the correlation between Hammett substituent constants and the enantiomeric excess, and the electron-releasing group at the meta- and para-positions of substituted benzaldehydes were demonstrated to be associated with the high enantioselectivity of the trimethylsilylcyanation reaction that involves trimethylsilylcyanide.
- Lee, Pei-Ting,Chen, Chinpiao
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p. 2704 - 2710
(2007/10/03)
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- Asymmetric cyanosilylation of aldehydes catalyzed by novel organocatalysts
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A novel proline-based N,N′-dioxide, which is easily prepared from inexpensive chemicals, serves as an effective catalyst for enantioselective cyanosilylation of aldehydes in up to 73% ee. Georg Thieme Verlag Stuttgart.
- Wen, Yuehong,Huang, Xiao,Huang, Jinglun,Xiong, Yan,Qin, Bo,Feng, Xiaoming
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p. 2445 - 2448
(2007/10/03)
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- Ionic liquid [omim][PF6] as an efficient and recyclable reaction media for the cyanosilylation of aldehydes without Lewis acid or any special activation
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Ionic liquid [omim][PF6] has been demonstrated as an efficient and environmentally friendly reaction media as well as a promoter for the cyanosilylation of aldehydes under mild conditions. In addition, the recovered ionic liquid could be reused for subsequent runs with only a gradual decrease in activity.
- Shen, Zhi-Liang,Ji, Shun-Jun,Loh, Teck-Peng
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p. 3137 - 3139
(2007/10/03)
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- Synthesis of some new chiral bifunctional o-hydroxyarylphosphonodiamides and their application as ligands in Ti(IV) complex catalyzed asymmetric silylcyanation of aromatic aldehydes
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Some new chiral bifunctional o-hydroxyarylphosphonodiamides were synthesized starting from (+)-cis-1,2,2-trimethylcyclopentane-1,3-diamine and the absolute configuration of the phosphorus atom was determined by X-ray diffraction analysis. Excellent enantioselectivity (up to 98% ee) was achieved in asymmetric silylcyanation of aromatic aldehydes using a chiral titanium complex formed in situ from Ti(OiPr)4 and o-hydroxyarylphosphonodiamide as the catalyst. Graphical Abstract.
- He, Ke,Zhou, Zhenghong,Wang, Lixin,Li, Kangying,Zhao, Guofeng,Zhou, Qilin,Tang, Chuchi
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p. 10505 - 10513
(2007/10/03)
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- Highly enantioselective cyanosilylation of aldehydes catalyzed by novel β-amino alcohol-titanium complexes
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The β-amino alcohol 1b-Ti(Oi-Pr)4 complex has been shown to catalyze the enantioselective cyanosilylation of aldehydes efficiently. In the presence of 5 mol % of 1b-Ti(Oi-Pr)4 complex catalyst, the aromatic, conjugated, heteroaromatic, and aliphatic aldehydes were converted to their corresponding trimethylsilyl ethers of cyanohydrins in 90-99% yields with up to 94% ee under mild conditions.
- Li, Yan,He, Bin,Qin, Bo,Feng, Xiaoming,Zhang, Guolin
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p. 7910 - 7913
(2007/10/03)
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- Lipase-catalyzed enantioselective transesterification toward esters of 2-bromo-tolylacetic acids
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Lipases from Candida antarctica, Pseudomonas cepacia and Rhizomucor miehei were tested in the resolution of seven racemic substrates belonging to the (RS)-2-bromo tolyl acetate ester category, but differing either in the position of the methyl substituent on the acyl part of the aromatic ring, or in the structure of the alkyl group. Lipase-catalyzed kinetic resolution via transesterification reaction between the ester and octanol in octane revealed that, of the three enzymes tested, P. cepacia lipase is the most efficient for resolution of the various racemates, with R-enantiopreference. In addition, the position of the methyl substituent was found to play a key role in governing the enantioselectivity of the reaction. Using P. cepacia lipase and 2-bromo-m/p-tolyl- or 2-bromophenylacetic acid esters E-values of 6.
- Guieysse, David,Salagnad, Christophe,Monsan, Pierre,Remaud-Simeon, Magali
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p. 317 - 323
(2007/10/03)
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