- 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
-
supporting information
p. 8259 - 8266
(2017/06/28)
-
- 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
-
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
-
p. 3098 - 3103
(2015/02/02)
-
- 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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- 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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- A simple separation method for (S)-hydroxynitrile lyase from cassava and its application in asymmetric cyanohydrination
-
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)
-
- Unsymmetric salen ligands bearing a Lewis base: Intramolecularly cooperative catalysis for cyanosilylation of aldehydes
-
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
-
supporting information; experimental part
p. 6323 - 6330
(2011/10/09)
-
- Highly active bifunctional salenTi(IV) catalysts for asymmetric cyanosilylation of aldehydes and TMSCN
-
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
-
scheme or table
p. 1285 - 1288
(2012/01/17)
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- Enantioselective silylcyanation of aldehydes catalyzed by new chiral oxovanadium complex
-
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
-
scheme or table
p. 1981 - 1984
(2012/03/10)
-
- Enzymatic kinetic resolution of racemic cyanohydrins via enantioselective acylation
-
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
-
experimental part
p. 624 - 630
(2010/09/07)
-
- 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
-
experimental part
p. 11367 - 11375
(2010/11/17)
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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
-
experimental part
p. 2834 - 2840
(2011/03/19)
-
- 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
-
experimental part
p. 726 - 737
(2011/04/23)
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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
-
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)
-
- A novel chiral (salen)AlIII complex catalyzed asymmetric cyanosilylation of aldehydes
-
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
-
experimental part
p. 1615 - 1618
(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)
-
- 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)
-
- A new (R)-hydroxynitrile lyase from Prunus mume: Asymmetric synthesis of cyanohydrins
-
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)
-
- 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
-
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
-
p. 2704 - 2710
(2007/10/03)
-
- 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)
-
- 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
-
p. 7910 - 7913
(2007/10/03)
-
- Tertiary pentyl groups enhance salen titanium catalyst for highly enantioselective trimethylsilylcyanation of aldehydes
-
tert-Pentyl groups are recognized to be highly effective steric groups that can enhance enantioselectivity of salen titanium complexes when they are used in asymmetrical cyanation of aromatic aldehydes. High ee (92-97%) has been obtained with several aldehyde substrates. Compared to its tert-butyl analogue, the tert-pentyl group has been found to improve enantioselectivity and in some cases quite dramatically.
- Liang, Sidney,Bu, Xiu R.
-
p. 2702 - 2704
(2007/10/03)
-
- Asymmetric trimethylsilylcyanation of aldehydes catalyzed by chiral schiff base-Ti(OiPr)4 complex
-
A new chiral Schiff base 4 was synthesized, which was found to be efficient catalyst for the enantioselective silylcyanation of aldehydes. The enantioselectivities of 25.1-72.7% were obtained by using the chiral Schiff base-Ti(OiPr)4 complex.
- Yang,Zhou,Tang
-
p. 3031 - 3036
(2007/10/03)
-
- Highly enantioselective cyanosilylation of aldehydes catalyzed by a Lewis acid-Lewis base bifunctional catalyst
-
A new bifunctional asymmetric catalyst containing a Lewis acid and a Lewis base (1) was developed and applied to the catalytic asymmetric cyanosilylation of aldehydes. The products were obtained generally with excellent enantiomeric excess. The experiment
- Hamashima, Yoshitaka,Sawada, Daisuke,Nogami, Hiroyuki,Kanai, Motomu,Shibasaki, Masakatsu
-
p. 805 - 814
(2007/10/03)
-
- Synthesis of new chiral Schiff bases and their application in the asymmetric trimethylsilylcyanation of aromatic aldehydes
-
The new chiral Schiff base ligands 1a-1c were synthesized from (1R)-(+)-camphor and found to be efficient catalysts for the enantioselective silylcyanation of aromatic aldehydes. The corresponding aromatic cyanohydrins were obtained in good yields and with enantiomeric excesses (e.e.s) of up to 73%.
- Yang, Zhuo-Hong,Wang, Li-Xin,Zhou, Zheng-Hong,Zhou, Qi-Lin,Tang, Chu-Chi
-
p. 1579 - 1582
(2007/10/03)
-
- CAL-B catalyzed enantioselective synthesis of cyanohydrins - A facile route to versatile building blocks
-
A straightforward process for the preparation of optically active cyanohydrins, important building blocks for the synthesis of drugs and agrochemicals, has been established. Lipase B from Candida antarctica (CAL-B) catalyzes the kinetic resolution of racemic cyanohydrin acetates under mild conditions: optimization of the process led to a user-friendly synthesis of (S)- and (R)-cyanohydrins.
- Hanefeld,Li,Sheldon,Maschmeyer
-
p. 1775 - 1776
(2007/10/03)
-
- Titanium and ruthenium binaphthyl Schiff base complexes as catalysts for asymmetric trimethylsilylcyanation of aldehydes
-
Investigations on the catalytic behaviour of titanium complexes formed in situ from Ti(OPri)4 and a variety of Schiff bases, mainly the binaphthyl derivatives 2,2′-bis(3-R1-5-R 2-2-hydroxybenzylideneamino)-1,1′-binaphthyl, toward the asymmetric trimethylsilylcyanation of some aromatic and aliphatic aldehydes demonstrated that the titanium complex of the binaphthyl Schiff base with R1 = R2 = But is one of the best catalysts for such a process, with an enantiomeric excess (e.e.) as high as 96% obtained for m-tolualdehyde. Crystal structure determination of a nitrosylruthenium complex, [RuII(L)(NO)Cl] (L is the dianion of the binaphthyl Schiff base with R1 = R2 = Cl), revealed that the complex assumes a cis-β configuration with the binaphthyl moiety having a dihedral angle of 70.2°. After treatment with AgPF6, the ruthenium complex also exhibited a good catalytic property for the trimethylsilylcyanation of benzaldehyde albeit with a lower e.e. (24%). The Royal Society of Chemistry 1999.
- Zhou, Xiang-Ge,Huang, Jie-Sheng,Ko, Po-Hung,Cheung, Kung-Kai,Che, Chi-Ming
-
p. 3303 - 3309
(2007/10/03)
-
- Catalytic, asymmetric cyanohydrin synthesis mediated by lanthanide(III) chloride pybox complexes
-
Complexes formed between lanthanide trichlorides and 2,6- bis(substituted-2-oxazolin-2-yl)pyridine (pybox) ligands are effective catalysts for the enantioselective addition of trimethylsilylcyanide (TMSCN) to a range of aldehydes.
- Aspinall, Helen C.,Greeves, Nicholas,Smith, Peter M.
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p. 1763 - 1766
(2007/10/03)
-
- BMPD, a novel C2-chiral 1,3-diketone ligand; synthesis and application to an asymmetric catalytic reaction
-
The synthesis of BMPD, 1,3-bis(2-methylferrocenyl)-propane-1,3-dione, was achieved via the Claisen condensation of a homochiral ferrocenecarboxylate and an acetylferrocene derived from the same chiral formylferrocene. Several metal complexes were prepared to exemplify the complexation ability of BMPD. A BMPD-yttrium complex was found to act as a new catalyst for silylcyanation of aldehydes with remarkable efficiency. As little as 0.2 mol% of the complex catalyzed the reaction of benzaldehyde and cyanotrimethylsilane to afford the cyanohydrin in 95% yield with 87% ee.
- Abiko, Atsushi,Wang, Guo-Qiang
-
p. 11405 - 11420
(2007/10/03)
-
- (S)-naproxen as a derivatizing agent to determine enantiomeric excess of cyanohydrins by HPLC
-
An easy, inexpensive and accurate method to determine enantiomeric excess of cyanohydrins is described. The method consists in derivatization of cyanohydrins with (S)-naproxen chloride and the products analyzed by HPLC. The results of enantiomeric excess so determined are similar to those obtained with [Eu(hfc)3], as a chiral shift reagent, and analysis by 1H- NMR of the cyanohydrins.
- Solis, Aida,Luna, Hector,Perez, Herminia I.,Manjarrez, Norberto,Sanchez, Remedios,Gutierrez, Atilano
-
p. 8759 - 8762
(2007/10/03)
-
- Enantioselective trimethylsilylcyanation of aldehydes catalyzed by chiral lanthanoid alkoxides
-
The first example of enantioselective trimethylsilylcyanation of aldehydes catalyzed by chiral binaphthol and binaphthol-modified lanthanum alkoxides has been achieved, in which an obvious effect of substituents at the 3,3′-positions of BINOL on the enantioselectivity was observed and 3,3′-bis(methoxyethyl)-BINOL had the advantage over simple BINOL to give (S)-products in excellent yields with 73% ee.
- Qian, Changtao,Zhu, Chengjian,Huang, Taisheng
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p. 2131 - 2132
(2007/10/03)
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- Asymmetric addition of trimethylsilyl cyanide to aldehydes catalysed by chiral (salen)TiIV complexes
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The asymmetric addition of trimethylsilyl cyanide to a range of aldehydes is catalysed by the titanium(IV) complexes of chiral salen derivatives 3-6. The enantiomeric excess of the resulting cyanohydrins is predominantly dependent upon the structure of the aldehyde, with electron-rich aromatic aldehydes giving best results. Electron-deficient aromatic aldehydes give cyanohydrins with low enantiomeric excesses, whilst ketones fail to react.
- Belokon', Yuri,Flego, Massimilano,Ikonnikov, Nicolai,Moscalenko, Margarita,North, Michael,Orizu, Charles,Tararov, Vitali,Tasinazzo, Michela
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p. 1293 - 1295
(2007/10/03)
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- (R)- and (S)-cyanohydrins using oxynitrilases in whole cells
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Almond meal and Sorghum bicolor shoots were used as the sources of oxynitrilases for the preparation of a number (R)- and (S)-arylcyanohydrins, respectively, from the corresponding aldehydes in diisopropyl ether. Two different in situ methods were used to introduce hydrogen cyanide into the reaction mixture. In method 1, acetone cyanohydrin decomposes enzymatically and/or chemically to hydrogen cyanide. In method 2, hydrogen cyanide freely evaporates from a solution in diisopropyl ether from one compartment of the reaction vessel and ends up to the other where it dissolves into the reaction mixture.
- Kiljunen, Eero,Kanerva, Liisa T.
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p. 1105 - 1116
(2007/10/03)
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- Asymmetric Carbon-Carbon Bond Forming Reactions Catalyzed by Chiral Schiff Base-Titanium Alkoxide Complexes
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The enantioselective addition of trimethylsilyl cyanide to a variety of aldehydes proceeded by the aid of a catalyst prepared in situ from titanium tetraisopropoxide and chiral Schiff bases and gave the corresponding cyanohydrins in high optical yield (up to 96percent e.e.).A remarkable rate enhancement was brought about by the addition of the Schiff base to the titanium alkoxide mediated silylcyanation of aldehydes.This catalyst system also promoted the highly enantioselective reaction of diketene with aldehydes, which led to the formation of optically active 5-hydroxy-3-oxoesters.
- Hayashi, Masahiko,Inoue, Tetsuya,Miyamoto, Yasunori,Oguni, Nobuki
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p. 4385 - 4398
(2007/10/02)
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- Enantioselective Trimethylsilylcyanation of Some Aldehydes Catalyzed by Chiral Schiff Base-Titanium Alkoxide Complexes
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A variety of aldehydes (aromatic, heteroaromatic, α,β-unsaturated, and nonconjugate aliphatic aldehydes) has been trimethylsilylcyanated in highly enantiomeric excess (ee) with a catalyst prepared in situ from titanium tetraisopropoxide and chiral Schiff bases.A remarkable rate enhancement was brought about by the addition of the Schiff base into the titanium alkoxide mediated silylcyanation of aldehydes.The chemical structure of chiral Schiff base-titanium alkoxide complexes is discussed based on their 13C NMR spectra, field desorption (FD) mass spectra, and molecular weights.
- Hayashi, Masahiko,Miyamoto, Yasunori,Inoue, Tetsuya,Oguni, Nobuki
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p. 1515 - 1522
(2007/10/02)
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- Enantioselective Trimethylsilylcyanation of some Aldehydes Catalysed by Titanium Alkoxide-Chiral Dialkyl Tartrate Complexes
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Highly enantioselective trimethylsilylcyanation of various aldehydes with trimethylsilyl cyanide has been achieved with a modified Sharpless catalyst, consisting of titanium tetraisopropoxide i)4> and chiral diisopropyl tartrate (DIPT).Asymmetric amplification was also observed in the trimethylsilylcyanation of benzaldehyde with a catalyst composed of Ti(OPri)4 and partially resolved DIPT.
- Hayashi, Masahiko,Matsuda, Tohru,Oguni, Nobuki
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p. 3135 - 3140
(2007/10/02)
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- Enantioselective Trimethylsilylcyanation of Some Aldehydes by Chiral Titanium Schiff's Base Complexes
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The complexes formed between titanium tetraalkoxide and chiral Schiff's bases make excellent catalysts for enantioselective trimethylsilylcyanation of aldehydes to optically active cyanohydrins in high optical yield.
- Hayashi, Masahiko,Miyamoto, Yasunori,Inoue, Tetsuya,Oguni, Nobuki
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p. 1752 - 1753
(2007/10/02)
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- ENZYME-CATALYZED SYNTHESIS OF (S)-CYANOHYDRINS AND SUBSEQUENT HYDROLYSIS TO (S)-α-HYDROXY-CARBOXYLIC ACIDS
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(S)-Cyanohydrins 2 are obtained with high enantioselectivity from aromatic aldehydes and HCN in the presence of (S)-oxynitrilase (E.C.4.1.2.11).Acid-catalyzed hydrolysis of the cyanohydrins 2 affords the corresponding (S)-α-hydroxy carboxylic acids 3 without racemization.
- Effenberger, Franz,Hoersch, Brigitte,Foerster, Siegfried,Ziegler, Thomas
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p. 1249 - 1252
(2007/10/02)
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- Cyclo-((S)-leucyl-(S)-histidyl). A Catalyst for Asymmetric Addition of Hydrogen Cyanide to Aldehydes
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Asymmetric addition of hydrogen cyanide to various aldehydes in the presence of a catalytic amount of cyclo-((S)-leucyl-(S)-histidyl) affords the corresponding cyanohydrins in moderate to good optical yields.The reaction of benzaldehyde with hydrogen cyanide gives (S)-2-hydroxy-2-phenylacetonitrile (85percent, 55percent ee) whose stereochemistry is found to be opposite to our previous result using cyclo-((S)-phenylalanyl-(S)-histidyl).
- Mori, Atsunori,Ikeda, Yoshitaka,Kinoshita, Koichi,Inoue, Shohei
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p. 2119 - 2122
(2007/10/02)
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- Asymmetric Hydrocyanation of a Range of Aromatic and Aliphatic Aldehydes
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A range of aryl, alkyl and heterocyclic aldehydes have been treated with hydrogen cyanide in the presence of the 'Inoue' catalyst, (R,R)- or (S,S)-cyclo.Most aryl aldehydes with electron-donating substituents in the m-or p-positions give high enantiomeric excess (e.e) values (>=80percent) but aryl aldehydes with strong electron-withdrawing substituents gave moderate e.e. values (=50percent).These moderate values are believed to be due to partial racemization of the product cyanohydrins in the presence of the mildly basic catalyst.In contrast to the reactions of aryl aldehydes, reactions of alkyl aldehydes and of ketones gave low e.e. values (=30percent) and an explanation is proposed.
- Matthews, Barry R.,Jackson, W. Roy,Jayatilake, Gamini S.,Wilshire, Colin,Jacobs, Howard A.
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p. 1697 - 1710
(2007/10/02)
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- Asymmetric Addition of Hydrogen Cyanide to Substituted Benzaldehydes Catalyzed by a Synthetic Cyclic Peptide, Cyclo((S)-phenylalanyl-(S)-histidyl)
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Using cyclo((S)-phenylalanyl-(S)-histidyl) as catalyst, optically active cyanohydrins from substituted benzaldehydes with p-methyl, m-methyl, o-methyl, m-methoxyl, or m-phenoxyl group were obtained with optical yield of 82-33percent.For the asymmetric cyanohydrin synthesis, nonpolar solvent such as benzene or carbon tetrachloride was advantageous, while on asymmetric synthesis took place in methanol or dimethyl sulfoxide.
- Kobayashi, Yoshiyuki,Asada, Shoichi,Watanabe, Ichigen,Hayashi, Hiroaki,Motoo, Yoshiyuki,Inoue, Shohei
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p. 893 - 896
(2007/10/02)
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