- Self-assembly of a homochiral nanoscale metallacycle from a metallosalen complex for enantioselective separation
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(Chemical Presented) Only half may enter: A homochiral porous nanoscale metallacycle has been efficiently self-assembled from semiflexible enantiopure metallosalen complexes with complementary coordination motifs. Single crystals of the macromolecule (see structure; C gray, Zn purple, O red, N blue) show a reversible and controllable dynamic behavior. Particularly, the metallacycle can be used to resolve small racemic alcohols with high enantioselectivity (over 99.0% ee).
- Li, Gao,Yu, Weibin,Ni, Jia,Liu, Taifeng,Liu, Yan,Sheng, Enhong,Cui, Yong
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- Enantiomerically enriched 1,2-P,N-bidentate ferrocenyl ligands for 1,3-dipolar cycloaddition and transfer hydrogenation reactions
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Novel complexes of 1,2-P,N-bidentate ferrocenyl ligands with AgOAc or with [RuCl2(PPh3)3] as catalysts have been studied in asymmetric synthesis. The catalytic activity of these systems have been studied in [3+2]-cycloaddition of azomethine ylides with olefins and the asymmetric transfer hydrogenation of ketones.
- Utepova, Irina A.,Serebrennikova, Polina O.,Streltsova, Marina S.,Musikhina, Alexandra A.,Fedorchenko, Tatiana G.,Chupakhin, Oleg N.,Antonchick, Andrey P.
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- Hydroboration. 92. Investigation of Practical Methods for the Synthesis of Optically Pure Isopinocampheylchloroborane for the Asymmetric Hydroboration of Representative Prochiral Alkenes
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A quantitative study was made of the preparation of the optically pure borane reagent, isopinocampheylchloroborane (IpcBHCl), potentially valuable for asymmetric hydroboration.IpcBHCl (87-90percent) in equilibrium with 5-6.5percent of IpcBCl2 and IpcBH2, respectively, can be prepared conveniently by a number of relatively simple operations: (1) the reaction of isopinocampheylborane (IcpBH2) with anhydrous hydrochloric acid (HCl) in ethyl ether (EE); (2) the reaction of stoichiometric amounts of IpcBH2 with isopinocampheyldichloroborane (IpcBCl2) in EE; and (3) the reduction of IpcBCl2 with trimethylsilane (Me3SiH) or lithium aluminum hydride (LAH) in EE.The reduction of IpcBCl2 with Me3SiH in pentane proceeds extremely slowly to provide the desired reagent, IpcBHCl.However, in EE, the reduction proceeds much faster, providing an equilibrium mixture of 90percent IpcBHCl, 5percent IpcBH2, and 5percent IpcBCl2.We also investigated the reduction of IpcBCl2 with Me3SiH in pentane and dichloromethane (CH2CL2) in the presence of known amounts of EE, tetrahydrofuran (THF), and dimethyl sulfide (SMe2), solvents which coordinate with the dichloroboranes.A comparative study of the rate of hydroboration of the alkene, 2-methyl-2-butene, with IpcBH2 and IpcBHCl, obtained as described above, was made in representative solvents, such as pentane, CH2Cl2, EE, and THF, at 0 deg C and, in many cases, also at 25 deg C.This study revealed that the rate of hydroboration is faster in THF for IpcBH2, while for IpcBHCl, the rate is faster in EE.Asymmetric hydroboration of prochiral alkenes was achieved by two methods, viz., IpcBHCl, produced by the reaction of IpcBH2 with HCl in EE (method A), and the reduction-hydroboration reaction of IpcBCl2 with LAH (0.25 equiv) in the presence of the prochiral alkene (method B) in EE.In both methods, the temperature of the reaction mixture was maintained at -25 deg C.Almost identical results were realized in these two procedures, with the enantiomeric excess (ee) realized with IpcBHCl, in some cases, considerably better than that achieved with IpcBH2.Although, IpcBHCl was obtained in onyl 87090percent purity along with IpcBH2 and IpcBCl2 as side products, the presence of the latter compound had no observable effect on the chiral outcome of the asymmetric hydroboration.
- Dhokte, Ulhas P.,Kulkarni, Shekhar V.,Brown, Herbert C.
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- Isopinocampheylbromoborane, a new promising reagent for the asymmetric hydroboration of prochiral alkenes
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A new promising in situ generated hydroborating agent, isopinocampheylbromoborane (IpcBHBr), achieves the asymmetric hydroboration of representative prochiral alkenes in pentane at lower temperatures, even at -78 °C, than has been possible with isopinocampheylborane (IpcBH2) and isopinocampheylchloroborane·EE (IpcBHCl·EE) reagents, usually in higher enantioselectivities than previously achieved. This is first time that the asymmetric hydroboration of prochiral alkenes with an α-pinene-derived borane reagent (IpcBHBr) has been achieved at such low temperature, -78 °C, in a relatively short time, 4-6 h. Copyright (C) 1996 Elsevier Science Ltd.
- Dhokte, Ulhas P.,Brown, Herbert C.
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- Asymmetric reduction of simple aliphatic ketones with dried cells of Geotrichum candidum
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Simple aliphatic ketones such as 2-pentanone, 2-butanone, 3-hexanone, etc., were reduced with high yield and excellent enantioselectivity to the corresponding (S)-alcohols using dried cells of Geotrichum candidum.
- Matsuda, Tomoko,Nakajima, Yuta,Harada, Tadao,Nakamura, Kaoru
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- Utilization of deep-sea microbial esterase PHE21 to generate chiral sec-butyl acetate through kinetic resolutions
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We previously identified and characterized 1 novel deep-sea microbial esterase PHE21 and used PHE21 as a green biocatalyst to generate chiral ethyl (S)-3-hydroxybutyrate, 1 key chiral chemical, with high enantiomeric excess and yield through kinetic resolution. Herein, we further explored the potential of esterase PHE21 in the enantioselective preparation of secondary butanol, which was hard to be resolved by lipases/esterases. Despite the fact that chiral secondary butanols and their ester derivatives were hard to prepare, esterase PHE21 was used as a green biocatalyst in the generation of (S)-sec-butyl acetate through hydrolytic reactions and the enantiomeric excess, and the conversion of (S)-sec-butyl acetate reached 98% and 52%, respectively, after process optimization. Esterase PHE21 was also used to generate (R)-sec-butyl acetate through asymmetric transesterification reactions, and the enantiomeric excess and conversion of (R)-sec-butyl acetate reached 64% and 43%, respectively, after process optimization. Deep-sea microbial esterase PHE21 was characterized to be a useful biocatalyst in the kinetic resolution of secondary butanol and other valuable chiral secondary alcohols.
- Wang, Yilong,Xu, Yongkai,Zhang, Yun,Sun, Aijun,Hu, Yunfeng
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- Dilongifolylborane: A New Effective Chiral Hydroborating Agent with Intermediate Steric Requirements
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Dilongifolylborane, (Lgf)2BH, a new effective chiral hydroborating agent, is readily synthesized from (+)-longifolene.Thus, treatment of (+)-longifolene with borane-methyl sulfide (BH3*SMe2) in ethyl ether rapidly precipitates snow-white crystalline (Lgf)2BH: mp 160-161 deg C; dimer; IR 1565 cm-1.The new chiral dialkylborane achieves the successful asymmetric hydroboration of cis, trisubstituted acyclic, and trisubstituted cyclic prochiral olefins to provide alcohols, after oxidation of the intermediate organoboranes, with optical purities in the range of 60-78percent ee.In the cases studied, the new asymmetric center at the alcohol position is predominantly the R enantiomer.
- Jadhav, Prabhakar K.,Brown, Herbert C.
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- Hydroboration. 83. Synthesis and Hydroboration of 2-Ethylapopinene. Comparison of Monoisopinocampheylborane and Its 2-Ethyl Analogue for the Chiral Hydroboration of Representative Alkenes
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Reduction of nopol tosylate gives the new chiral ligand (-)-2-ethylapopinene (90.2percent ee) with higher steric requirements than those of α-pinene.Reaction of borane with (-)-2-ethylapopinene in THF at 0 deg C, in a molar ratio of 1:2, provides an equilibrium mixture of mono- and dialkylboranes EapBH2 and Eap2BH.With an excess of (-)-2-ethylapopinene (1:10; BMS/2-ethylapopinene), the formation of bis(2-ethylapoisopinocampheyl)borane, Eap2BH, is essentially quantitative (ca. 98percent).Treatment of the equilibrium mixture of boranes (Eap2BH, EapBH2) with TMED at 34 deg C precipitates crystalline (EapBH2)2*TMED.Treatment of the crystalline product with BF3*OEt2 gives EapBH2 (mono(2-ethylapoisopinocampheyl)borane) of essentially 100percent ee, enantiomerically purer than the (-)-2-ethylapopinene (ca. 90percent ee) utilized for the preparation.Hydroboration of a series of olefins with EapBH2, followed by oxidation of the intermediate organoborane, produces the corresponding alcohols with significantly improved enantiomeric purities over those realized with IpcBH2 under the same conditions.Liberation of the olefin from purified EapBH2 provides (-)-2-ethylapopinene (D23 -46.2 deg (neat) in high optical purity (>99percent ee).Metalation of (+)-α-pinene (D23 +51.4 deg (neat)) with the Lochmann reagent, followed by alkylation with methyl iodide, provides in high optical purity (>99percent ee) (+)-2-ethylapopinene (D23 +46.4 deg (neat)), unavailable from commercial (-)-nopol.
- Brown, Herbert C.,Randad, Ramnarayan S.,Bhat, Krishna S.,Zaidlewicz, Marek,Weissman, Steven A.,et al.
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- Chiral nanoscale metal-organic tetrahedral cages: Diastereo-selective self-assembly and enantioselective separation
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(Figure Presented) Cage rage: Chiral tetrahedral cages are diastereoselectively self-assembled from enantiopure C2-symmetric biphenyl bis(β-diketonate) linkers and C3-symmetric octahedral Fe3+ or Ca3+ ions (see picture; Fe purple, C blue, O red; cavity shown as an orange sphere). The porous polyhedra exhibit metal-dependent chiroptical behavior and act as hosts for the crystallization separation of racemic alcohols with up to 99.5% ee.
- Liu, Taifeng,Liu, Yan,Xuan, Weimin,Cui, Yong
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- Asymmetric transfer hydrogenation of alkyl/aryl or alkyl/methyl ketones catalyzed by known C2-symmetric ferrocenyl-based chiral bis(phosphinite)-Ru(II), Rh(I) and Ir(III) complexes
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Known Ru(II), Rh(I) and Ir(III) complexes of C2-symmetric ferrocenyl based chiral bis(phoshinite) ligands were catalyzed the asymmetric transfer hydrogenation of alkyl/aryl or alkyl methyl ketones. Corresponding secondary alcohols were obtained with high enantioselectivities up to 98% ee and reactivities using iso-propanol as the hydrogen source.
- Durap, Feyyaz,Karaka?, Duygu Elma,Ak, Bünyamin,Baysal, Akin,Aydemir, Murat
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- Evaluation of Pseudoenantiomeric Mixed Carbonates as Efficient Fluorogenic Probes for Enantioselectivity Screening
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We report mixed carbonates as enzyme substrates and demonstrate their application as fluorogenic probes for lipase and esterase enantiopreference screening. By the application of pseudoenantiomers with distinct fluorescence behaviors, it is possible to evaluate the activity and enantiopreference of hydrolytic enzymes. In order to validate our method, enantioselectivities calculated from fluorometric measurements were compared with the results obtained from larger-scale kinetic resolution. Pseudoenantiomeric mixed carbonates with distinct fluorogenic properties are shown to be very useful probes for screening lipase and esterase enantioselectivity. The simultaneous use of pseudoenantiomeric substrates overcomes conventional assays with single enantiomer substrates, as the effects of competitive binding are taken into account.
- Zadlo, Anna,Koszelewski, Dominik,Borys, Filip,Ostaszewski, Ryszard
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- Preparation and characterization of the chirally modified rapidly quenched skeletal Ni catalyst for enantioselective hydrogenation of butanone to R-(-)-2-butanol
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A rapidly quenched skeletal Ni (RQ Ni) prepared by the melt-spinning method followed by alkali leaching was used as a new category of Ni precursor to fabricate effective chiral Ni catalyst. A series of tartaric acid (TA)-NaBr-modified RQ Ni catalysts (MRQNi) were derived, and the textural and structural properties of the MRQNi catalysts were systematically investigated. It is found that the modification conditions influence profoundly the composition, texture, and Ni crystallite size of the MRQNi catalysts. In liquid phase hydrogenation of butanone to R-(-)-2-butanol, the optimized MRQNi catalyst exhibits much better activity and enantioselectivity than the similarly chirally modified Raney Ni catalyst. Based on the characterizations, the superior catalytic performance of the MRQNi catalyst is mainly attributed to the higher surface content of the sodium-nickel(II) tartrate complex than that on the chirally modified Raney Ni catalyst.
- Lou, Zhiying,Chen, Xueying,Tian, Li,Qiao, Minghua,Fan, Kangnian,He, Heyong,Zhang, Xiaoxin,Zong, Baoning
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- 2-Isopropylapoisopinocampheylborane, An Improved Reagent for the Asymmetric Hydroboration of Representative Prochiral Alkenes
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A new hydroborating agent, 2-isopropylapoisopinocampheylborane (iPraBH2, 2f), achieves the asymmetric hydroboration of representative prochiral alkenes in higher optical purities than that achieved by the borane derivatives, 2-organylapoisopinocampheylboranes (R = Me, IpcBH2; R = Et, EapBH2; and R = Ph, PapBH2) previously examined.
- Dhokte, Ulhas P.,Brown, Herbert C.
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- Discovery and Redesign of a Family VIII Carboxylesterase with High (S)-Selectivity toward Chiral sec-Alcohols
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Highly enantioselective lipase has been widely utilized in the preparation of versatile enantiopure chiral sec-alcohols through kinetic or dynamic kinetic resolution. Lipase is intrinsically (R)-selective, and it is difficult to obtain (S)-selective lipase. Recent crystal structures of a family VIII carboxylesterase have revealed that the spatial array of its catalytic triad is the mirror image of that of lipase but with a catalytic triad that is distinct from lipase. We, therefore, hypothesized that the family VIII carboxylesterase may exhibit (S)-enantioselectivity toward sec-alcohols similar to (S)-selective serine protease, whose catalytic triad is also spatially arrayed as its mirror image. In this study, a homologous enzyme (carboxylesterase from Proteobacteria bacterium SG_bin9, PBE) of a known family VIII carboxylesterase (pdb code: 4IVK) was prepared, which showed not only moderate (S)-selectivity toward sec-alcohols such as 3-butyn-2-ol and 1-phenylethyl alcohol but also (R)-selectivity toward particular sec-alcohols among the substrates explored. Furthermore, the (S)-selectivity of PBE has been significantly improved by rational redesign based on molecular modeling. Molecular modeling identified a binding pocket composed of Ser381, Ala383, and Arg408 for the methyl substituent of (R)-1-phenylethyl acetate and suggested that larger residues may increase the enantioselectivity by interfering with the binding of the slow-reacting enantiomer. As predicted, substituting Ser381with larger residues (Phe, Tyr, and Trp) significantly improved the (S)-selectivity of PBE toward all sec-alcohols explored, even the substrates toward which the wild-type PBE exhibits (R)-selectivity. For instance, the enantioselectivity toward 3-butyn-2-ol and 1-phenylethyl alcohol was improved from E = 5.5 and 36.1 to E = 2001 and 882, respectively, by single mutagenesis (S381F).
- Park, Areum,Park, Seongsoon
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p. 2397 - 2402
(2022/02/17)
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- Novel highly efficient absolute optical resolution method by serial combination of two asymmetric reactions from acetylene monomers having racemic substituents
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For general optical resolution, an optical resolution agent is necessary, and the best agent should be selected for each racemic compound. In this study, we will report that a novel optical resolution method by circularly polarized light (CPL) without any
- Aoki, Toshiki,Kaneko, Takashi,Liu, Lijia,Suzuki, Junpei,Tang, Yanan,Teraguchi, Masahiro
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supporting information
p. 450 - 461
(2022/01/15)
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- Half-sandwich rhodium complex with ortho-position carborane benzoxazole structure as well as preparation method and application of half-sandwich rhodium complex
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The invention relates to a half-sandwich rhodium complex with an ortho-position carborane benzoxazole structure as well as a preparation method and application of the half-sandwich rhodium complex. The structural formula of the rhodium complex is shown in the specification. The preparation method comprises the following steps: firstly, adding an n-BuLi solution into an ortho-position carborane solution, and then reacting for 30-60 minutes at room temperature; adding bromo-benzoxazole, and carrying out a reaction for 6-8 h at a room temperature; and adding [Cp * RhCl2] 2, reacting at room temperature for 3-5 hours, and carrying out post-treatment to obtain the rhodium complex. The rhodium complex can be used as a catalyst to catalyze the asymmetric reduction reaction of aliphatic chiral alcohol compounds synthesized from aliphatic ketones. Compared with the prior art, the rhodium complex disclosed by the invention has the advantages of simple preparation method, stable physicochemical properties, high catalytic activity for asymmetric reduction reaction of aliphatic ketone, mild reaction conditions and the like.
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Paragraph 0051-0056
(2021/03/24)
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- London Dispersion Interactions Rather than Steric Hindrance Determine the Enantioselectivity of the Corey–Bakshi–Shibata Reduction
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The well-known Corey–Bakshi–Shibata (CBS) reduction is a powerful method for the asymmetric synthesis of alcohols from prochiral ketones, often featuring high yields and excellent selectivities. While steric repulsion has been regarded as the key director of the observed high enantioselectivity for many years, we show that London dispersion (LD) interactions are at least as important for enantiodiscrimination. We exemplify this through a combination of detailed computational and experimental studies for a series of modified CBS catalysts equipped with dispersion energy donors (DEDs) in the catalysts and the substrates. Our results demonstrate that attractive LD interactions between the catalyst and the substrate, rather than steric repulsion, determine the selectivity. As a key outcome of our study, we were able to improve the catalyst design for some challenging CBS reductions.
- Eschmann, Christian,Song, Lijuan,Schreiner, Peter R.
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supporting information
p. 4823 - 4832
(2021/02/01)
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- Boron containing chiral Schiff bases: Synthesis and catalytic activity in asymmetric transfer hydrogenation (ATH) of ketones
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Asymmetric Transfer Hydrogenation (ATH) has been an attractive way for the reduction of ketones to chiral alcohols. A great number of novel and valuable synthetic pathways have been achived by the combination usage of organometallic and coordination chemistry for the production of important class of compounds and particularly optically active molecules. For this aim, four boron containing Schiff bases were synthesized by the reaction of 4-formylphenylboronic acid with chiral amines. The boron containing structures have been found as stable compounds due to the presence of covalent B–O bonds and thus could be handled in laboratory environment. They were characterized by 1H NMR and FT-IR spectroscopy and elemental analysis and they were used as catalyst in the transfer hydrogenation of ketones to the related alcohol derivatives with high conversions (up to 99%) and low enantioselectivities (up to 22% ee).
- Pa?a, Salih,Arslan, Nevin,Meri??, Nermin,Kayan, Cezmi,Bingül, Murat,Durap, Feyyaz,Aydemir, Murat
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- Enantioselective transfer hydrogenation of pro-chiral ketones catalyzed by novel ruthenium and iridium complexes of well-designed phosphinite ligand
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The interaction of [Ru(η6-arene)(μ-Cl)Cl]2 and Ir(η5-C5Me5)(μ-Cl)Cl]2 with a new Ionic Liquid-based phosphinite ligand, [(Ph2PO)-C6H9N2Ph]Cl, (2) gave [Ru((Ph2PO)-C6H9N2Ph)(η6-p-cymene)Cl2]Cl (3), [Ru((Ph2PO)-C6H9N2Ph)(benzene)Cl2]Cl (4) and [Ir((Ph2PO)-C6H9N2Ph)(C5Me5)Cl2]Cl (5), complexes. All the compounds were characterized by a combination of multinuclear NMR and IR spectroscopy as well as elemental analysis. Furthermore, the Ru(II) and Ir(III) catalysts were applied to asymmetric transfer hydrogenation of acetophenone derivatives using 2-propanol as a hydrogen source. The results showed that the corresponding alcohols could be obtained with good activity (up to 55% ee and 99% conversion) under mild conditions. Notably, [Ir((Ph2PO)-C6H9N2Ph)(C5Me5)Cl2]Cl (5) is more active than the other analogous complexes in the transfer hydrogenation (up to 81% ee).
- Arslan, Nevin
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p. 628 - 637
(2020/01/02)
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- Synthesis of cis-1,2-diol-type chiral ligands and their dioxaborinane derivatives: Application for the asymmetric transfer hydrogenation of various ketones and biological evaluation
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Two cis-1,2-diol-type chiral ligands (T1 and T2) and their tri-coordinated chiral dioxaborinane (T(1–2)B(1–2)) and four-coordinated chiral dioxaborinane adducts with 4-tert-butyl pyridine sustained by N → B dati
- Kilic, Ahmet,Balci, Tu?ba Ersayan,Arslan, Nevin,Aydemir, Murat,Durap, Feyyaz,Okumu?, Veysi,Tekin, Recep
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- Catalysts for the asymmetric transfer hydrogenation of various ketones from [3-[(2S)-2-[(diphenylphosphanyl)oxy]-3-phenoxypropyl]-1-methyl-1H-imidazol-3-ium chloride] and [Ru(η6-arene)(μ-Cl)Cl]2, Ir(η5-C5Me5)(μ-Cl)Cl]2 or [Rh(μ-Cl)(cod)]2
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The combination of [3-[(2S)-2-[(diphenylphosphanyl)oxy]-3-phenoxypropyl]-1-methyl-1H-imidazol-3-ium chloride] with [Ru(η6-arene)(μ-Cl)Cl]2, Ir(η5-C5Me5)(μ-Cl)Cl]2 or [Rh(μ-Cl)(cod)]2, in the presence of KOH/isoPrOH, has been found to generate catalysts that are capable of enantioselectively reducing alkyl, aryl ketones to the corresponding (R)-alcohols. Under optimized conditions, when the catalysts were applied to the asymmetric transfer hydrogenation, we obtained the secondary alcohol products in high conversions and enantioselectivities using only 0.5 mol% catalyst loading. In addition, [3-[(2S)-2-{[(chloro(?4-1,5-cyclooctadiene)rhodium)diphenyl phosphanyl] oxy}-3-phenoxypropyl]-1-methyl-1H-imidazol-3-ium chloride], (6) complex is much more active than the other analogous complexes in the transfer hydrogenation. Catalyst 6 acts as excellent catalysts, giving the corresponding (R)-1-phenyl ethanol in 99% conversion in 30 min (TOF ≤ 396 h?1) and in high enantioselectivity (92% ee).
- Meri?, Nermin,Arslan, Nevin,Kayan, Cezmi,Rafikova, Khadichakhan,Zazybin, Alexey,Kerimkulova, Aygul,Aydemir, Murat
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p. 108 - 118
(2019/04/17)
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- One-Pot Absolute Stereochemical Identification of Alcohols via Guanidinium Sulfate Crystallization
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A novel technique for the absolute stereochemical determination of alcohols has been developed that uses crystallization of guanidinium salts of organosulfates. The simple one-pot, two-step process leverages facile formation of guandinium organosulfate single crystals for the straightforward determination of the absolute stereochemistry of enantiopure alcohols by means of X-ray crystallography. The strong hydrogen bonding network drives the stability of the crystal lattice and allows for a diverse range of organic alcohol substrates to be analyzed.
- Brummel, Beau R.,Lee, Kinsey G.,McMillen, Colin D.,Kolis, Joseph W.,Whitehead, Daniel C.
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supporting information
p. 9622 - 9627
(2019/12/02)
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- Upcycling a plastic cup: One-pot synthesis of lactate containing metal organic frameworks from polylactic acid
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Waste PLA can be upcycled to metal organic frameworks of potential high value in a one-pot synthesis scheme, where PLA depolymerisation occurs in situ. Three homochiral lactate based frameworks were successfully synthesised and characterised from PLA as a feed source, including ZnBLD. The chiral separation ability of ZnBLD was maintained.
- Slater, Benjamin,Wong, So-On,Duckworth, Andrew,White, Andrew J. P.,Hill, Matthew R.,Ladewig, Bradley P.
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supporting information
p. 7319 - 7322
(2019/06/27)
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- A new class of well-defined ruthenium catalysts for enantioselective transfer hydrogenation of various ketones
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A pair of novel optically pure phosphinite ligands were synthesized by ring opening reaction of chiral amines with (R)-styrene oxide or (S)-glycidyl phenyl ether oxide using a straightforward method in high yields and their ruthenium complexes were described in detail. The ruthenium complexes proved to be highly efficient catalysts for the enantioselective hydrogenation of ketones, affording products up to 99% ee. The results showed that the corresponding chiral alcohols could be obtained with high activity and excellent enantioselectivities at the desired temperature. (2S)-1-{benzyl[(1S)-1-(naphthalen-1-yl)ethyl]amino}-3-phenoxypropan-2-yl diphenylphosphinito[dichloro(η6-benzene)ruthenium (II)] acts an excellent catalyst in the reduction of ketones, giving the corresponding alcohol up to 99% ee.
- Kayan, Cezmi,Meri?, Nermin,Rafikova, Khadichakhan,Zazybin, Alexey,Gürbüz, Nevin,Karakaplan, Mehmet,Aydemir, Murat
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- Chiral C2-symmetric η6-p-cymene-Ru(II)-phosphinite complexes: Synthesis and catalytic activity in asymmetric reduction of aromatic, methyl alkyl and alkyl/aryl ketones
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Chiral C2-symmetric bis(phosphinite) ligands and their binuclear ruthenium(II) complexes have been synthesized and used as catalysts in the ruthenium-catalyzed asymmetric transfer hydrogenation of aromatic, methyl alkyl and alkyl/aryl ketones using 2-propanol as both the hydrogen source and solvent in the presence of KOH. Under optimized conditions, all complexes showed high catalytic activity as catalysts in the reduction of various ketones to corresponding chiral secondary alcohols. Products were obtained with high conversions (99%) and moderate to good enantioselectivities (82% ee). Furthermore, C2-symmetric bis(phosphinite) ligands and their binuclear ruthenium(II) complexes were characterized by multinuclear NMR spectroscopy, FT-IR spectroscopy, LC/MS-MS and elemental analysis.
- Karaka?, Duygu Elma,Aydemir, Murat,Durap, Feyyaz,Baysal, Ak?n
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p. 430 - 439
(2017/12/06)
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- Synthesis and characterization of novel silica coated magnetic nanoparticles with tags of β-cyclodextrin: application as an eco-friendly and chiral micro-vessel catalyst in the enantioselective reduction of ketones
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In this work, we report the synthesis of a novel, green and recoverable organic–inorganic magnetic nanocomposite by grafting β-cyclodextrin on the surface of a silica-coated magnetic nanoparticle, Fe3O4@SiO2/Pr-β-CD. FT-IR spectroscopy, transmission electron microscopy, CHN analysis, thermogravimetric analysis, vibrating sample magnetometer and X-ray diffraction analyses confirmed its structure. The magnetic core–shell structured modified silica microsphere has been successfully used as a chiral micro-vessel catalyst for the enantioselective reduction of ketones by NaBH4. The described catalyst was regenerated and reused without any significant changes in the yield and enantiomeric excess.
- Jafari Nasab, Mina,Kiasat, Ali Reza
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p. 2719 - 2728
(2018/02/06)
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- Homochiral Metal-Organic Cage for Gas Chromatographic Separations
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Metal-organic cages (MOCs) as a new type of porous material with well-defined cavities were extensively pursued because of their relative ease of synthesis and their potential applications in host-guest chemistry, molecular recognition, separation, catalysis, gas storage, and drug delivery. Here, we first reported that a homochiral MOC [Zn3L2] is explored to fabricate [Zn3L2] coated capillary column for high-resolution gas chromatographic separation of a wide range of analytes, including n-alkanes, polycyclic aromatic hydrocarbons, and positional isomers, especially for racemates. Various kinds of racemates such as alcohols, diols, epoxides, ethers, halohydrocarbons, and esters were separated with good enantioselectivity and reproducibility on the [Zn3L2] coated capillary column. The fabricated [Zn3L2] coated capillary column exhibited significant chiral recognition complementary to that of a commercial β-DEX 120 column and our recently reported homochiral porous organic cage CC3-R coated column. The results show that the homochiral MOCs will be very attractive as a new type of chiral selector in separation science.
- Xie, Sheng-Ming,Fu, Nan,Li, Li,Yuan, Bao-Yan,Zhang, Jun-Hui,Li, Yan-Xia,Yuan, Li-Ming
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p. 9182 - 9188
(2018/07/21)
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- New functional chiral P-based ligands and application in ruthenium-catalyzed enantioselective transfer hydrogenation of ketones
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Metal-catalyzed asymmetric transfer hydrogenation is a powerful and practical method for the reduction of ketones to produce the corresponding secondary alcohols, which are valuable building blocks in the pharmaceutical, perfume, and agrochemical industries. Hence, a series of novel chiral β-amino alcohols were synthesized by chiral amines with regioselective ring opening of (S)-propylene oxide or reaction with (S)-(+)-2-hydroxypropyl p-toluenesulfonate by a straightforward method. The chiral ruthenium catalytic systems generated from [Ru(arene)(μ-Cl)Cl]2 complexes and chiral phosphinite ligands based on amino alcohol derivatives were employed in asymmetric transfer hydrogenation of ketones to give the corresponding optically active alcohols; (2S)-1-{[(2S)-2-[(diphenylphosphanyl)oxy]propyl][(1R)-1-phenylethyl]amino}propan-2-yldiphenylphosphinitobis[dichol-oro(η6-benzene)ruthenium(II)] acts an excellent catalyst in the reduction of α-naphthyl methyl ketone, giving the corresponding alcohol with up to 99% ee. The substituents on the backbone of the ligands were found to have a remarkable effect on both the conversion and enantioselectivity of the catalysts. Furthermore, this transfer hydrogenation is characterized by low reversibility under these conditions.
- Meri?, Nermin,Kayan, Cezmi,Gürbüz, Nevin,Karakaplan, Mehmet,Binbay, Nil Ertekin,Aydemir, Murat
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p. 1739 - 1749
(2017/10/26)
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- Chiral phosphinites as efficient ligands for enantioselective Ru(II), Rh(I) and Ir(III)-catalyzed transfer hydrogenation reactions
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Abstract: Metal-catalyzed enantioselective transfer reduction of ketones to enantiomerically enriched chiral alcohols has recently attracted attention. Therefore, a series of methyl alkyl or alkyl/aryl ketones have been reduced by using Ru(II), Rh(I) and Ir(III) catalysts based on C2-symmetric chiral ferrocenyl phosphinite ligands. The corresponding optically active secondary alcohols were obtained in excellent conversions and moderate-to-good enantioselectivities. The best results were obtained with an iridium catalyst, giving up to 98% conversion and 80% ee.
- Baysal, Ak?n,Elma Karaka?, Duygu,Meri?, Nermin,Ak, Bünyamin,Aydemir, Murat,Durap, Feyyaz
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p. 365 - 372
(2017/04/18)
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- Missing Linker Defects in a Homochiral Metal-Organic Framework: Tuning the Chiral Separation Capacity
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Efficient chiral separation remains a very challenging task due to the identical physical and chemical properties of the enantiomers of a molecule. Enantiomers only behave differently from each other in the presence of other chiral species. Homochiral metal-organic frameworks (MOFs) have received much attention for their promising enantioseparation properties. However, there are still challenges to overcome in this field such as high enantiomeric separation. Structural defects play an important role in the properties of MOFs and can significantly change the pore architecture. In this work, we introduced missing linker defects into a homochiral metal-organic framework [Zn2(bdc)(l-lac)(dmf)] (ZnBLD; bdc = 1,4-benzenedicarboxylic acid, l-lac = l-lactic acid, dmf = N,N′-dimethylformamide) and observed an increase in enantiomeric excess for 1-phenylethanol of 35% with the defective frameworks. We adjusted the concentration of monocarboxylic acid ligand l-lactic acid by varying the ratio of Zn2+ to ligand from 0.5 to 0.85 mmol. Additionally, a defective framework was synthesized with propanoic acid as modulator. In order to elucidate the correlation between defects and enantiomeric excess, five characterization techniques (FTIR, TGA, 1H NMR, ICP, and PXRD) were employed. Full width at half-maximum analysis (fwhm) was performed on the powder X-ray diffraction traces and showed that the higher concentration of monocarboxylic acid MOFs were isostructural but suffered from increased fwhm values.
- Slater, Benjamin,Wang, Zeru,Jiang, Shanxue,Hill, Matthew R.,Ladewig, Bradley P.
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supporting information
p. 18322 - 18327
(2017/12/15)
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- Enantioselective transfer hydrogenation of various ketones with novel efficient iridium(III) ferrocenyl-phosphinite catalysts
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The asymmetric reduction of prochiral ketones is a pivotal reaction for the preparation of chiral alcohols which form an extremely important class of intermediates for fine chemicals and pharmaceuticals. Especially, iridium-based asymmetric reduction of ketones to enantiomerically enriched alcohols has recently attracted important attention by a number of research groups and interest in this area is growing. Therefore, a series of novel neutral mononuclear iridium(III) ferrocenyl-phosphinite complexes have been prepared and applied in the iridium(III)-catalyzed asymmetric transfer hydrogenation (ATH) of ketones to give corresponding secondary alcohols with outstanding enantioselectivities and reactivities using 2-propanol as the hydrogen source (up to 99% ee and 99% conversion). It was seen that the substituents on the backbone of the ligands resulted in a significant effect on both the activity and % enantioselectivity. Furthermore, the structural elucidation of the complexes was carried out by elemental analysis, IR and multi-nuclear NMR spectroscopic data.
- Meri?, Nermin,Aydemir, Murat
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p. 120 - 128
(2016/07/13)
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- Chiral polyethers derived from BINOL and ECH as highly enantioselective and efficient catalysts for the borane reduction of prochiral ketones
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Two novel polyethers derived from BINOL were synthesized and used to induce the enantioselective borane reduction of prochiral ketones. The polyethers gave the expected secondary alcohols with up to 98% yields and over 99% ee values. The recovered polyethers could be reused for many times to induce the enantioselective reduction of prochiral ketones without losing their enantioselective induction ability.
- Zhang, An-Lin,Yu, Zeng-Da,Yang, Li-Wen,Yang, Nian-Fa,Peng, Dan
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p. 407 - 412
(2015/01/30)
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- Asymmetric reduction of ketones catalyzed by α,α-diphenyl-(L)-prolinol modified with imidazolium ionic liquid and BH3·SMe2 as a recoverable catalyst
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The synthesis of α,α-diphenyl-4-trans-hydroxy-(L)-prolinol modified with imidazolium based ionic liquids was carried out with trans-α,α-diphenyl-4-hydroxy-(L)-prolinol, 5-bromovaleric acid or 1,5-dibromopentane and imidazole. α,α-Diphenyl-4-hydroxy-(L)-prolinol modified with imidazolium ionic liquid was treated with BH3·SMe2 which generate 1,3,2-oxazaborolidine, that acts as a catalyst for asymmetric reduction of prochiral ketones. α,α-Diphenyl-4-hydroxy-(L)-prolinol modified with imidazolium ionic liquids (PF6 anion) with BH3?SMe2 found to be an efficient catalyst (10 mol%) for the reduction of the acetophenone, gave 99% yield and 87-84% ee. The catalytic method has wide applicability for a variety of substrates. 1,3,2-oxazaborolidine containing ether linkage ionic liquid was recovered and reused up to 4 cycles with 99-91% yields and 87-81% ee's.
- Chauhan, ManMohan Singh,Singh, Surendra
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p. 184 - 189
(2015/02/19)
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- Synthesis of several polyethers derived from BINOL and their application in the asymmetric borane reduction of prochiral ketones
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Several novel epoxy monomers, (S,S)- or (S,R)-3-(glycidyloxy)methyl-2,2′-bis(methoxymethyloxy)-1,1′-binaphthalene and (S,S)- or (S,R)-6-(glycidyloxy)methyl-2,2′-bis(methoxymethyloxy)-1,1′-binaphthalene, which were derived from chiral BINOL and epichlorohydrin, were synthesized and underwent anionic polymerization and deprotection of the MOM groups to obtain soluble polyethers. These polyethers were used to induce the enantioselective borane reduction of prochiral ketones. The substrates gave up to 98% yield with over 99% ee values. The recovered polyethers could be reused many times to induce the enantioselective reduction of prochiral ketones without losing their enantioselective induction ability.
- Zhang, An-Lin,Yu, Zeng-Da,Yang, Li-Wen,Yang, Nian-Fa
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p. 173 - 179
(2015/03/04)
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- Discrimination of the prochiral hydrogens at the C-2 position of n-alkanes by the methane/ammonia monooxygenase family proteins
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The selectivity of ammonia monooxygenase from Nitrosomonas europaea (AMO-Ne) for the oxidation of C4-C8n-alkanes to the corresponding alcohol isomers was examined to show the ability of AMO-Ne to recognize the n-alkane orientation within the catalytic site. AMO-Ne in whole cells produces 1- and 2-alcohols from C4-C8n-alkanes, and the regioselectivity is dependent on the length of the carbon chain. 2-Alcohols produced from C4-C7n-alkanes were predominantly either the R- or S-enantiomers, while 2-octanol produced from n-octane was racemic. These results indicate that AMO-Ne can discriminate between the prochiral hydrogens at the C-2 position, with the degree of discrimination varying according to the n-alkane. Compared to the particulate methane monooxygenase (pMMO) of Methylococcus capsulatus (Bath) and that of Methylosinus trichosporium OB3b, AMO-Ne showed a distinct ability to discriminate between the orientation of n-butane and n-pentane in the catalytic site.
- Miyaji, Akimitsu,Miyoshi, Teppei,Motokura, Ken,Baba, Toshihide
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p. 8261 - 8270
(2015/08/03)
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- Highly efficient hydroxylation of gaseous alkanes at reduced temperature catalyzed by cytochrome P450BM3 assisted by decoy molecules
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Cytochrome P450BM3 functions as a small-alkane hydroxylase upon the addition of perfluorocarboxylic acids (PFs) as decoy molecules. The coupling efficiency (product formation rate per NADPH consumption rate) for the hydroxylation of small alkanes was improved by reducing the reaction temperature to 0°C.
- Kawakami, Norifumi,Cong, Zhiqi,Shoji, Osami,Watanabe, Yoshihito
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p. 329 - 334
(2015/05/13)
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- Cobalt(II) complexes with bis-2,4-[N-(S)-phenylalanyl]-6-chlorotriazine: Synthesis, structure, and application for separation of enantiomers of butan-2-ol
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The chiral coordination compounds [Co(L)(H2O)2(MeOH)] n (1) and Co2(L)2(H2O)(MeOH)4 (2) were synthesized by the reaction of bis-2,4-[N-(S)-phenylalanyl]6-chlorotriazine (LH2) with cobalt(II) pivalate or acetate. In molecules 2, the CoII ions are linked by a bridging water molecule and two carboxy groups of the L2- anion. By passing the racemate of butan-2-ol through a chromatographic column containing complex 1 as the stationary phase, a mixture enriched with the (S)-isomer of this alcohol can be obtained.
- Satskaya, Yu. A.,Komarova,Gavrilenko,Manoylenko,Kiskin,Kolotilov,Eremenko,Novotortsev
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p. 630 - 635
(2015/11/27)
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- Bioreductions catalyzed by an alcohol dehydrogenase in non-aqueous media
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Highly productive biocatalytic reductions were established using an isolated alcohol dehydrogenase (ADH) under water-deficient conditions. First, a solvent-free system was evaluated for the reduction of 2-butanone catalyzed by ADH evo-1.1.200 promoted by the "smart cosubstrate" 1,4-butanediol. ADH evo-1.1.200 excelled by its activity and stability under high reagent concentrations and hence was the enzyme of choice. However, conversion of 2-butanone was limited to 1 % in 10 days under the solvent-free conditions. Therefore, water-immiscible organic solvents were evaluated whereby the highest conversions were achieved in MTBE and toluene. MTBE was chosen as its different boiling point compared to other reaction components (e.g., 2-butanone, 2-butanol, diol cosubstrate, and lactone coproduct) would simplify the downstream processing. Further on, by tuning substrate loading, the productivity of the ADH evo-1.1.200 was successfully increased to a turnover number (TON) of 64 000. Practical water-deficient enzymology for bioreductions: The use of alcohol dehydrogenases (ADHs) in neat substrates and in water-immiscible organic solvents is explored. The ADH evo-1.1.200 excelled by its high stability, as it showed significant catalytic activity over days. Reductions are coupled with the "smart cosubstrate" 1,4-butanediol; hence, excess amounts of reductants are avoided.
- Kara, Selin,Spickermann, Dominik,Weckbecker, Andrea,Leggewie, Christian,Arends, Isabel W. C. E.,Hollmann, Frank
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p. 973 - 976
(2014/05/06)
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- Stereospecific Pd-catalyzed cross-coupling reactions of secondary alkylboron nucleophiles and aryl chlorides
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We report the development of a Pd-catalyzed process for the stereospecific cross-coupling of unactivated secondary alkylboron nucleophiles and aryl chlorides. This process tolerates the use of secondary alkylboronic acids and secondary alkyltrifluoroborates and occurs without significant isomerization of the alkyl nucelophile. Optically active secondary alkyltrifluoroborate reagents undergo cross-coupling reactions with stereospecific inversion of configuration using this method.
- Li, Ling,Zhao, Shibin,Joshi-Pangu, Amruta,Diane, Mohamed,Biscoe, Mark R.
-
supporting information
p. 14027 - 14030
(2015/01/08)
-
- Synthesis of four stereoisomers of (S)-2-methylpent-3-yl 3,13-dimethylpentadecanoate, a sex pheromone of the bagworm moth clania variegate, using stereospecific inversion of secondary sulfonates as a key step
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Females of some lepidopteran species produce novel sex pheromones with a methyl-branched structure, such as 2-methylpent-3-yl 3,13-dimethylpentadecanoate secreted by the bagworm moth Clania variegate. Recently, we have established a simple preparative method for the synthesis of methyl-branched building blocks by utilizing an SN2 reaction of chiral secondary tosylates derived from (S)- and (R)-propylene oxides. The usefulness of these building blocks was demonstrated by their application in the synthesis of all four stereoisomers of an acid moiety in the bagworm pheromone. The enantiomeric purities of all building blocks were confirmed by enantioselective HPLC analysis. We found that a secondary mesylate was superior to the corresponding tosylate because it avoided an elimination side reaction, and racemization in the SN2 reaction was not observed even at high temperature (150 °C). Finally, each optically active acid was esterified with (S)-2-methyl-3-pentanol, which was synthesized by a new route starting from (S)-valine. A simple route to methyl-branched building blocks has been developed by utilizing an S N2 reaction of chiral secondary sulfonates derived from (S)- and (R)-propylene oxides. The usefulness of these building blocks was demonstrated by the stereospecific synthesis of all four stereoisomers of a bagworm pheromone. Copyright
- Taguri, Tomonori,Yamamoto, Masanobu,Fujii, Toru,Muraki, Yuta,Ando, Tetsu
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p. 6924 - 6933
(2013/11/06)
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- Macrocyclic Mn(III) salen complexes as recyclable catalyst for oxidative kinetic resolution of secondary alcohols
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New macrocyclic chiral Mn(III) salen complexes (C1-C4) were synthesized and were used as catalysts for oxidative kinetic resolution (OKR) of secondary alcohols with diacetoxyiodobenzene (PhI(OAc)2) and N-bromosuccinimide (NBS), in biphasic dichloromethane: water solvent mixture. Good to excellent enantioselectivities were achieved with catalyst C2 for several secondary alcohols having different steric environment. In general with catalyst C2, NBS as a co-oxidant showed better enantioselectivity than PhI(OAc)2 in OKR. The catalyst C2 was easily retrieved from the reaction mixture by the addition of hexane and recycled seven times both with NBS and PhI(OAc) 2 as co-oxidants without losing its performance. Based on the experimental results a mechanism for OKR of racemic 1-phenylethanol has been proposed where (R,R)-Mn-salen preferably binds with (S)-1-phenylethanol to give (R)-1-phenylethanol in excess at the end of the reaction.
- Bera, Prasanta Kumar,Maity, Nabin Ch.,Abdi, Sayed H.R.,Khan, Noor-Ul H.,Kureshy, Rukhsana I.,Bajaj, Hari C.
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p. 542 - 551
(2013/09/24)
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- MCl2(ampy)(dppf) (M = Ru, Os): Multitasking catalysts for carbonyl compound/alcohol interconversion reactions
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The easily accessible complexes [MCl2(dppf)(ampy)] (M = Ru (cis-1), Os (trans-2); dppf = 1,1′-bis(diphenylphosphino)ferrocene; ampy = 2-aminomethylpyridine) in the presence of base (NaOiPr, KOtBu) are efficient catalysts for several reactions involving carbonyl compounds and alcohols. The derivatives 1 and 2 catalyze the selective transfer hydrogenation of aldehydes and ketones to alcohols with 2-propanol using 0.1-0.005 mol % of catalyst at 82 °C with TOF values up to 3.0 × 105 h-1. These compounds (0.1-0.02 mol %) promote the hydrogenation of aldehydes and ketones in EtOH or a MeOH/EtOH mixture at 30-90 °C (5 atm of H2) and the acceptorless dehydrogenation of alcohols to ketones in tBuOH at 130-145 °C (0.4 mol %). Complexes 1 and 2 (0.5 mol %) catalyze the racemization of chiral alcohols at 70 °C in 2-propanol and the isomerization of allylic alcohols to ketones in tBuOH at 70-120 °C (1 mol %). In addition, 1 and 2 (0.5 mol %) promote the α alkylation of α-tetralone with primary alcohols (EtOH, nPrOH, and nBuOH) at 120 °C in a tBuOH/toluene mixture (1/2 v/v). Complex 2 is easily obtained in 93% yield from [OsCl2(PPh3) 3], dppf, and ampy in toluene.
- Putignano, Elisabetta,Bossi, Gianluca,Rigo, Pierluigi,Baratta, Walter
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experimental part
p. 1133 - 1142
(2012/04/04)
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- Enantioselective sorption of alcohols in a homochiral metal-organic framework
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Single-crystal X-ray diffraction study reveals the host-guest interactions between a homochiral metal-organic framework and two enantiomers of a chiral alcohol providing the key driving force for the enantioselective sorption of alcohols in the framework.
- Suh, Kyungwon,Yutkin, Maxim P.,Dybtsev, Danil N.,Fedin, Vladimir P.,Kim, Kimoon
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supporting information; experimental part
p. 513 - 515
(2012/01/19)
-
- Screening method for the evaluation of asymmetric catalysts for the reduction of aliphatic ketones
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ATH reductions of aliphatic ketones in water catalyzed by ruthenium coordinated by prolinamide ligands produce alcohols with moderate enantiomeric excesses in most cases. A set of seven aliphatic ketones is proposed for a rapid evaluation of the enantioselectivity of catalysts by one-pot multi-substrates reduction. The screening of a library of prolinamides shows that according to the structure of the ketones different ligands give the best asymmetric inductions.
- Boukachabia, Mourad,Zeror, Saoussen,Collin, Jacqueline,Fiaud, Jean-Claude,Zouioueche, Louisa Aribi
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supporting information; experimental part
p. 1485 - 1489
(2011/05/16)
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- Inclusion of aliphatic alcohols in pockets of (S)-threonyl-(S)- phenylglycine using grinding method
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Inclusion compounds of a dipeptide, (S)-threonyl-(S)-phenylglycine (Thr-Phg), with several aliphatic alcohols were easily prepared by grinding them in a mortar. Thr-Phg molecules arranged in antiparallel to construct a sheet, and guest alcohols were accommodated in a chiral pocket between the sheets. 3-Butyn-2-ol and 2-butanol were included with moderate enantioselectivity, 57% ee (R) and 49% ee (R), respectively. The role of the hydroxy group of Thr-Phg is not only to construct the unique pocket but also to capture guest alcohols by hydrogen bonding.
- Akazome, Motohiro,Toma, Shusaku,Horiguchi, Tatsunori,Megumi, Ken,Matsumoto, Shoji
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experimental part
p. 2844 - 2848
(2011/05/06)
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- Construction of hydrogen-bonded ternary organic crystals derived from L -tartaric acid and their application to enantioseparation of secondary alcohols
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Ternary organic crystals consisting of an L-tartaric acid-derived dicarboxylic acid, a commercially available achiral diamine, and a chiral secondary alcohol have been developed and characterized by X-ray crystallography. 1D, 2D, and 3D hydrogen-bonded supramolecular networks were constructed, depending on the structure of the diamine used. Benzylic and aliphatic secondary alcohols were enantioselectively incorporated into the crystal and were successfully enantioseparated with up to 86 and 79 % enantiomeric excess (ee), respectively. Selective incorporation of one enantiomer of 2-butanol, which is a small chiral aliphatic alcohol, was achieved by the cooperative effects of hydrogen bonds, CH...π interactions, and van der Waals interactions between the guest and host molecules, with the aid of two water molecules. The high host potential of the binary supramolecular system is mainly attributed to the skewed conformation of two rigid aromatic groups of tartaric acid derivatives, which prevents dense packing of the molecules and enhances the formation of multicomponent inclusion crystals.
- Kodama, Koichi,Sekine, Eriko,Hirose, Takuji
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experimental part
p. 11527 - 11534
(2011/11/29)
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- Enantioselectivity of haloalkane dehalogenases and its modulation by surface loop engineering
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In the loop: Engineering of the surface loop in haloalkane dehalogenases affects their enantiodiscrimination behavior. The temperature dependence of the enantioselectivity (lnE versus 1/T) of β-bromoalkanes by haloalkane dehalogenases is reversed (red data points) by deletion of the surface loop; the selectivity switches back when an additional single-point mutation is made. This behavior is not observed for -bromoesters.
- Prokop, Zbynek,Sato, Yukari,Brezovsky, Jan,Mozga, Tomas,Chaloupkova, Radka,Koudelakova, Tana,Jerabek, Petr,Stepankova, Veronika,Natsume, Ryo,Van Leeuwen, Jan G. E.,Janssen, Dick B.,Florian, Jan,Nagata, Yuji,Senda, Toshiya,Damborsky, Jiri
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supporting information; experimental part
p. 6111 - 6115
(2010/11/05)
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- Chiral ligand derived from (1S,2R)-norephedrine as a catalyst for enantioselective prochiral ketone reduction
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Chiral oxazaborolidines derived from (1S,2R)-(+)-norephedrine and substituted salicylaldehydes were employed in the asymmetric reduction of prochiral ketones using borane dimethyl sulfide as a reducing agent. The secondary alcohols were formed in excellent yields (45-99.8%) with enantioselectivities up to 99.8%. The effect of the substitution in the aromatic ring of the ligand was discussed with the enantioselectivity of the product.
- Balakrishnan, Umesh,Ananthi, Nallamuthu,Velmathi, Sivan
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experimental part
p. 1150 - 1153
(2009/09/27)
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- H-bonding as a control element in stereoselective Ru-catalyzed olefin metathesis
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(Chemical Equation Presented) H-bonding interactions have been exploitedextensively in the design of catalysts for stereoselective synthesis bu t have rarely been utilized in the development of metal-catalyzed processes. Studies described herein demonstrate that intramolecular H-bonding interactions can significantly increase the rate and levels of stereochemical control in Ru-catalyzed olefin metathesis reactions. The utility of H-bonding in catalytic olefin metathesis is elucidated through development of exceptionally facile and highly diastereoselective ring-opening/cross-metathesis (DROCM) reactions, involving achiral Ru catalysts and enantiomerically enriched allylic alcohols. Transformations proceed to completion readily (>98percent conversion, up to 87percent yield), often within minutes, in the presence of ≤2 mol percent of an achiral catalyst to afford synthetically versatile products of high stereochemical purity (up to >98:2 dr and 11:1 E:Z).
- Hoveyda, Amir H.,Lombardi, Pamela J.,O'Brien, Robert V.,Zhugralin, Adil R.
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supporting information; experimental part
p. 8378 - 8379
(2009/10/23)
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- Synthesis of three novel chiral diamines derived from (S)-proline and their evaluation as precursors of diazaborolidines for the catalytic borane-mediated enantioselective reduction of prochiral ketones
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A series of chiral diazaborolidine catalysts are readily prepared in situ at 75 °C in toluene solvent and under microwave irradiation (100 W, 15 min, air cooling) using chiral diamines derived from inexpensive and commercially available (S)-proline and borane-dimethyl sulfide. Special mention deserves the synthesis of potentially versatile diamine (S)-8 [(S)-(pyrrolidin-2-yl)diphenylmethanamine], with the key step being the conversion of tertiary alcohol (S)-(1-benzylpyrrolidin-2-yl)diphenyl methanol, (S)-12, to azide (S)-13. The chiral diazaborolidine/BH3 reagent system was successfully employed in the enantioselective reduction of prochiral ketones to give the corresponding secondary alcohols in excellent yield and with up to 96% enantiomeric purities.
- Luis Olivares-Romero,Juaristi, Eusebio
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experimental part
p. 9992 - 9998
(2009/04/11)
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- Gas-phase stereoselective binding to mn/salen catalysts
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Gas-phase equilibrium measurements have been used to determine the stereoselectivity of binding the enantiomers of 1-phenylethanol to manganese/salen asymmetric epoxidation catalysts. There is significant selectivity in the gas-phase binding, and the results are compared to data from condensed-phase epoxidations. The study demonstrates the utility of a novel internal standard approach that allows for rapid, accurate measures of the stereoselectivity of gas-phase ligand binding. Moreover, the data suggest that gas-phase binding stereoselectivity could be a potential predictor of condensed-phase enantioselectivity.
- Fagin, Adelaide E.,Wang, Guoping,Lau, Michel C.,Gronert, Scott
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body text
p. 1771 - 1773
(2009/05/26)
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- 9-Borabicyclo[3.3.2]decanes and the asymmetric hydroboration of 1,1-disubstituted alkenes
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The syntheses of the optically pure asymmetric hydroborating agents 1 (a, R = Ph; b, R = TMS) in both enantiomeric forms are reported. These reagents are effective for the hydroboration of cis-, trans- and trisubstituted alkenes. More significantly, they exhibit unprecedented levels of selectivity in the asymmetric hydroboration of 1,1-disubstituted alkenes (28-92% ee), a previously unanswered challenge in the nearly 50 year history of this reagent-controlled process. For example, the hydroboration of α-methylstyrene with 1a produces the corresponding alcohol 6f in 78% ee (cf., Ipc2BH, 5% ee). Suzuki coupling of the intermediate adducts 5 produces the nonracemic products 7 very effectively (50-84%) without loss of optical purity. Copyright
- Gonzalez, Ana Z.,Roman, Jose G.,Gonzalez, Eduvigis,Martinez, Judith,Medina, Jesus R.,Matos, Karl,Soderquist, John A.
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supporting information; experimental part
p. 9218 - 9219
(2009/02/02)
-
- PROCESS FOR THE HOMOGENEOUS HYDROGENATION OF KETONES USING RUTENIUM CATALYTIC SYSTEMS
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To have an industrial applicable process for the reduction of C1-C6 alkyl ketones (including prochiral) or their deuterated derivatives in huge quantities for obtaining their respective alcohols. To provide a new process for the preparation of secondary alcohols substituted with C1-C6 alkyl chain or their deuterated derivatives. The process comprises the hydrogenation of ketones (including prochiral) using Rutenium achiral or chiral catalytic systems to render racemic or nonracemic chiral alcohols or deuterated racemic or nonracemic chiral alcohols under low pressure and room temperature.
- -
-
Page/Page column 7-8
(2008/06/13)
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- Maximise equilibrium conversion in biphasic catalysed reactions: How to obtain reliable data for equilibrium constants?
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For the prediction and optimisation of the equilibrium conversion in biphasic catalysed reactions, the equilibrium constant of the desired reaction and the partition coefficients of all reactants have to be known. Within this contribution we have examined the alcohol dehydrogenase-catalysed reduction of several linear and aromatic ketones in biphasic reaction media with respect to equilibrium conversion. In this example, the equilibrium constant can be expressed in terms of differences in oxidation-reduction potentials ΔE0. However, for a large variety of organic compounds, these data are quite rare in the literature. To overcome this lack of data, we have utilised methods of computational chemistry to calculate data for the Gibbs free energy ΔGR leading to the equilibrium constants of a homologous series of linear ketones. To obtain comparable data for the reduction of substituted acetophenone derivatives, the Hammett relation leads to the necessary equilibrium constants. Furthermore, we compare the equilibrium conversions of a set of cofactor regeneration methods for the alcohol dehydrogenase-catalysed reductions. These results lead to a time-saving experimental design for the enantioselective reduction of 2-octanone to (R)-2-octanol on a preparative scale utilising biphasic reaction conditions.
- Eckstein,Lembrecht,Schumacher,Eberhard,Spiess,Peters,Roosen,Greiner,Leitner,Kragl
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p. 1597 - 1604
(2007/10/03)
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- Designing the "Search pathway" in the development of a new class of highly efficient stereoselective hydrosilylation catalysts
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A highly efficient class of N-heterocyclic carbene-based catalysts for the asymmetric hydrosilylation of prochiral ketones was discussed. The potential pitfalls associated with the nonlinearity in the behavior of an enantioselective catalyst in response to the variations of key reaction parameters were also described. The modular design of a new catalyst is based essentially on a single assembly step of its structural and functional subunits. It was observed that the direct coupling of oxazolines and N-heterocyclic carbenes leads to chelating C,N ancillary ligands for asymmetric catalysis that combines both an 'anchor' unit and a stereodirecting element.
- Cesar, Vincent,Beliemin-Laponnaz, Stephane,Wadepohl, Hubert,Gade, Lutz H.
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p. 2862 - 2873
(2007/10/03)
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- Efficient optical resolution of secondary alkyl alcohols by chiral supramolecular hosts
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A novel tunable multi-chiral supramolecular host system was developed from non-chiral dicarboxylic acid and (1R, 2R)-diphenylethylenediamine via chirality transfer, which enabled highly efficient optical resolution of secondary alkyl alcohols by simple crystallization of host compounds from alcohol solution. The Royal Society of Chemistry 2005.
- Imai, Yoshitane,Sato, Tomohiro,Kuroda, Reiko
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p. 3289 - 3291
(2007/10/03)
-
