- Discovery and Redesign of a Family VIII Carboxylesterase with High (S)-Selectivity toward Chiral sec-Alcohols
-
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
-
p. 2397 - 2402
(2022/02/17)
-
- A Cobalt(II) Complex Bearing the Amine(imine)diphosphine PN(H)NP Ligand for Asymmetric Transfer Hydrogenation of Ketones
-
Novel chiral cobalt complex a containing amine(imine)diphosphine PN(H)NP ligand and complex b containing bis(amine)diphosphine PN(H)N(H)P ligand were synthesized. The structures of two complexes were characterized by X-ray crystallography and high resolution mass spectrometry. The catalytic performances of cobalt complexes a and b for asymmetric transfer hydrogenation (ATH) of ketones under mild conditions were evaluated using 2-propanolisopropanol as solvent and hydrogen source after being activated by 8 equivalents of base. Complex a showed a good reactivity for reduction of ketones, with a turnover number (TON) of up to 555, and a maximum enantiomeric excess (ee) value of up to 91 %. Complex b exhibited inertness for hydrogenation of ketones. Electronic structure studies on a and b were conducted to account for the function of ligands on the catalytic performances.
- Huo, Shangfei,Chen, Hong,Zuo, Weiwei
-
supporting information
p. 37 - 42
(2020/10/21)
-
- London Dispersion Interactions Rather than Steric Hindrance Determine the Enantioselectivity of the Corey–Bakshi–Shibata Reduction
-
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.
-
p. 4823 - 4832
(2021/02/01)
-
- Conformationally Controlled Linear and Helical Hydrocarbons Bearing Extended Side Chains
-
Conformationally controlled flexible molecules are ideal for applications in medicine and materials, where shape matters but an ability to adapt to multiple and changing environments is often required. The conformation of flexible hydrocarbon chains bearing contiguous methyl substituents is controlled through the avoidance of syn-pentane interactions: alternating syn-anti isomers adopt a linear conformation while all-syn isomers adopt a helical conformation. From a simple diamond lattice analysis, larger substituents, which would be required for most potential applications, result in significant and unavoidable syn-pentane interactions, suggesting substantially reduced conformational control. Through a combination of computation, synthesis, and NMR analysis, we have identified a selection of substitution patterns that allow large groups to be incorporated on conformationally controlled linear and helical hydrocarbon chains. Surprisingly, when the methyl substituents of alternating syn-anti hydrocarbons are replaced with acetoxyethyl groups, the main chain of almost 95% of the population of molecules adopt a linear conformation. Here, the side chains adopt nonideal eclipsed conformations with the main chain, thus minimizing syn-pentane interactions. In the case of all-syn hydrocarbons, concurrent removal of some methyl groups on the main chain adjacent to the large substituents is required to maintain a high population of molecules adopting a helical conformation. This information can now be used to design flexible hydrocarbon chains displaying functional groups in a defined relative orientation for multivalent binding or cooperative reactivity, for example, in targeting the interfaces defined by disease-relevant protein-protein interactions.
- Aggarwal, Varinder K.,Butts, Craig P.,Davy, Matthew,Dutton, Oliver J.,Guo, Lin,Kucukdisli, Murat,Myers, Eddie L.,Wagnières, Olivier
-
supporting information
p. 16682 - 16692
(2021/10/21)
-
- 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
-
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
-
-
- Boron containing chiral Schiff bases: Synthesis and catalytic activity in asymmetric transfer hydrogenation (ATH) of ketones
-
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
-
-
- Enantioselective transfer hydrogenation of pro-chiral ketones catalyzed by novel ruthenium and iridium complexes of well-designed phosphinite ligand
-
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
-
p. 628 - 637
(2020/01/02)
-
- Chiral Imidazo[1,5- a]pyridine-Oxazolines: A Versatile Family of NHC Ligands for the Highly Enantioselective Hydrosilylation of Ketones
-
Herein we report the synthesis and application of a versatile class of N-heterocyclic carbene ligands based on an imidazo[1,5-a]pyridine-3-ylidine backbone that is fused to a chiral oxazoline auxiliary. The key step in the synthesis of these ligands involves the installation of the oxazoline functionality via a microwave-assisted condensation of a cyano-azolium salt with a wide variety of 2-amino alcohols. The resulting chiral bidentate NHC-oxazoline ligands form stable complexes with rhodium(I) that are efficient catalysts for the enantioselective hydrosilylation of structurally diverse ketones. The corresponding secondary alcohols are isolated in good yields (typically >90%) with good to excellent enantioselectivities (80-93% ee). The reported hydrosilylation occurs at ambient temperatures (40 °C), with excellent functional group tolerability. Even ketones bearing heterocyclic substituents (e.g., pyridine or thiophene) or complex organic architectures are hydrosilylated efficiently, which is discussed further in this report.
- Chinna Ayya Swamy,Varenikov, Andrii,Ruiter, Graham De
-
supporting information
p. 247 - 257
(2020/02/04)
-
- Diastereoselective Synthesis of P-Chirogenic and Atropisomeric 2,2′-Bisphosphino-1,1′-binaphthyls Enabled by Internal Phosphine Oxide Directing Groups
-
Diphosphine ligands that merge both axial and P-centered chirality may exhibit superior or unique properties. Herein we report the diastereoselective introduction of P-centered chirality at the 2-position of the axially chiral 2′-(phosphine oxide)-1,1′-binaphthyl scaffold. A lithium–bromide exchange reaction of a 2-bromo-2′-(phosphine oxide)-1,1′-binaphthyl and treatment with dichlorophosphines followed by a nucleophilic organometallic reagent afforded unsymmetrical 2-phosphino-2′-(phosphine oxide)-1,1′-binaphthyls with binaphthyl axial chirality and one or two phosphorus stereocenters with a variety of P substituents. The final diastereomerically pure 2,2′-bisphosphino-1,1′-binaphthyls were obtained by reduction of the phosphine oxide directing group. Preliminary results demonstrated that a ligand with this hybrid chirality could induce higher stereoselectivity in the metal-complex-catalyzed asymmetric hydrogenation of a dialkyl ketone.
- Huo, Shangfei,Li, Jianli,Wang, Tingyi,Wang, Zeming,Xue, Qingquan,Zhu, Meifang,Zuo, Weiwei
-
supporting information
p. 8153 - 8159
(2020/04/24)
-
- Iridium-catalyzed asymmetric hydrogenation method for the preparation of chiral alcohols
-
The present invention provides one kind of iridium-catalyzed asymmetric hydrogenation method for the preparation of chiral alcohols, the method specifically is: in the glove box filled with nitrogen, the [Ir (COD) Cl]2 With a chiral P, N, N ligand soluble in methanol, stir at room temperature 1 hour, [...] catalyst. Adding substrate alkone and alkali additive, is placed on the high-pressure in the reactor, for a certain reaction under the pressure of the hydrogenation reaction. Slowly release hydrogen, silica gel to remove the solvent and separate the product after the alcohol. The invention states iridium catalyzed alkone asymmetric hydrogenation for the preparation of chiral reaction has mild condition, easy to operate, and the product of the enantioselectivity and the like.
- -
-
Paragraph 0095-0100; 0103; 0104
(2019/06/07)
-
- Enantioselective Hydrogenation of Ketones using Different Metal Complexes with a Chiral PNP Pincer Ligand
-
The synthesis of different metal pincer complexes coordinating to the chiral PNP ligand bis(2-((2R,5R)-2,5-dimethyl-phospholanoethyl))amine is described in detail. The characterized complexes with Mn, Fe, Re and Ru as metal centers showed good activities regarding the reduction of several prochiral ketones. Comparing these catalysts, the non-noble metal complexes produced best selectivities not only for aromatic substrates, but also for different kinds of aliphatic ones leading to enantioselectivities up to 99% ee. Theoretical investigations elucidated the mechanism and rationalized the selectivity. (Figure presented.).
- Garbe, Marcel,Wei, Zhihong,Tannert, Bianca,Spannenberg, Anke,Jiao, Haijun,Bachmann, Stephan,Scalone, Michelangelo,Junge, Kathrin,Beller, Matthias
-
supporting information
p. 1913 - 1920
(2019/03/13)
-
- 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
-
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
-
p. 108 - 118
(2019/04/17)
-
- Biocatalytic Racemization Employing TeSADH: Substrate Scope and Organic Solvent Compatibility for Dynamic Kinetic Resolution
-
Racemization in combination with a kinetic resolution is the base for a dynamic kinetic resolution (DKR). Biocatalytic racemization was successfully performed for a broad scope of sec-alcohols by employing a single alcohol dehydrogenase (ADH) variant from Thermoanaerobacter pseudoethanolicus (formerly T. ethanolicus; TeSADH W110A I86A C295A). The catalyst employed as a lyophilized whole cell preparation or cell free extract, which tolerated various non-water miscible organic solvents under micro-aqueous or two-phase conditions, whereby cyclohexane and n-hexane suited best. Various concepts for combining the enzymatic racemization with an enzymatic kinetic resolution to achieve overall a bis-enzymatic DKR were evaluated. A proof of concept showed a successful DKR with racemization in aqueous phase combined with acylation in the organic phase.
- Pop?oński, Jaros?aw,Reiter, Tamara,Kroutil, Wolfgang
-
p. 763 - 768
(2018/02/27)
-
- 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
-
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
-
p. 430 - 439
(2017/12/06)
-
- A new class of well-defined ruthenium catalysts for enantioselective transfer hydrogenation of various ketones
-
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
-
-
- CHIRAL METAL COMPLEX COMPOUNDS
-
The invention comprises novel chiral metal complex compounds of the formula (I) wherein M, PR2, R3 and R4 are outlined in the description, its stereoisomers, in the form as a neutral complex or a complex cation with a suitable counter ion. The chiral metal complex compounds can be used in asymmetric reactions, particularly in asymmetric reductions of ketones, imines or oximes.
- -
-
Page/Page column 18; 19; 23; 24; 27
(2018/11/10)
-
- Chiral phosphinites as efficient ligands for enantioselective Ru(II), Rh(I) and Ir(III)-catalyzed transfer hydrogenation reactions
-
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
-
p. 365 - 372
(2017/04/18)
-
- Unsymmetrical Iron P-NH-P′ Catalysts for the Asymmetric Pressure Hydrogenation of Aryl Ketones
-
The reductive amination of α-dialkylphosphine acetaldehydes with enantiopure β-aminophosphines is a new, versatile route to unsymmetrical tridentate (pincer) ligands P-NH-P′. Four new ligands PR2CH2CH2NHCHR′CHR′′PPh2 (R=iPr, Cy, R′=Ph, CH(CH3)2, R′′=Ph, H) prepared in this way are used to make the iron(II) complexes mer-FeCl2(CO)(P-NH-P′) and mer-FeCl(H)(CO)(P-NH-P′). The hydride complex with the rigid ligand with R′=R′′=Ph is an efficient and highly enantioselective homogeneous asymmetric pressure hydrogenation (APH) catalyst. Prochiral aryl ketones are reduced under mild conditions (THF, 0.1 mol % catalyst, 1 mol % KOtBu, 5–10 bar, 50 °C) to the (S)-alcohols, usually in enantiomeric excess (ee) greater than 90 %. DFT calculations provided transition-state structures for the enantiodetermining hydride-transfer step.
- Smith, Samantha A. M.,Lagaditis, Paraskevi O.,Lüpke, Anne,Lough, Alan J.,Morris, Robert H.
-
p. 7212 - 7216
(2017/05/31)
-
- Manganese(I)-Catalyzed Enantioselective Hydrogenation of Ketones Using a Defined Chiral PNP Pincer Ligand
-
A new chiral manganese PNP pincer complex is described. The asymmetric hydrogenation of several prochiral ketones with molecular hydrogen in the presence of this complex proceeds under mild conditions (30–40 °C, 4 h, 30 bar H2). Besides high catalytic activity for aromatic substrates, aliphatic ketones are hydrogenated with remarkable selectivity (e.r. up to 92:8). DFT calculations support an outer sphere hydrogenation mechanism as well as the experimentally determined stereochemistry.
- Garbe, Marcel,Junge, Kathrin,Walker, Svenja,Wei, Zhihong,Jiao, Haijun,Spannenberg, Anke,Bachmann, Stephan,Scalone, Michelangelo,Beller, Matthias
-
supporting information
p. 11237 - 11241
(2017/09/02)
-
- Half-sandwich ruthenium catalyst bearing an enantiopure primary amine tethered to an N-heterocyclic carbene for ketone hydrogenation
-
By using a copper transmetalation reagent [Cu-(Kaibene)2]I, the NHC ligand (S,S)-MeNC3H2NCHPhCHPhNH2 "Kaibene" was transferred to ruthenium to make a precatalyst [RuCp?(Kaibene)(MeCN)](PF6) (Cp? = 1,2,3,4,5-pentamethylcyclopentadienyl), 7, in high yield as a mixture of two diastereomers. Under relatively mild conditions (0.02 mol % Ru, 0.16 mol % KOtBu, iPrOH, 50 °C, 25 bar of H2), this compound catalyzes the hydrogenation of aryl ketones and one alkyl ketone effectively with excellent activity and productivity (TOF up to 48 s-1, TON up to 104). At higher hydrogenation pressure (46 bar), the catalytic hydrogenation of N-phenyl-benzylimine to the corresponding amine is efficiently achieved. The hydrogenation of prochiral ketones resulted in low ee (35% for 4-chloroacetophenone). NMR spectroscopy was used to observe diastereomeric hydrides RuCp?(Kaibene)(H) 13-R/S that were generated by reaction of 7 with H2 and base in THF-d8. Complementary DFT studies suggest that either the heterolytic splitting of dihydrogen to form 13-R/S or the hydride transfer to the substrate can be rate-determining depending on the substrate. Experimental and computational results support mechanisms that involve the heterolytic splitting of dihydrogen to the nitrogen of the amide-ligated form of Kaibene in THF or the heterolytic splitting to an outer-sphere alkoxide derived from the product alcohol or 2-PrOH solvent. An unusual feature is the rapid drop in ee of the product alcohol from as high as 60% (R) to 0% in some cases; this might be due to racemization of the Kaibene ligand in THF caused by the strong base or competitive inhibition of one diastereomer of the catalyst by reaction with the product (R)-alcohol.
- Wan, Kai Y.,Sung, Molly M. H.,Lough, Alan J.,Morris, Robert H.
-
p. 6827 - 6842
(2017/11/06)
-
- Highly Enantioselective Hydrosilylation of Ketones Catalyzed by a Chiral Oxazaborolidinium Ion
-
A highly enantioselective hydrosilylation of ketones was developed for the synthesis of a variety of chiral secondary alcohols. In the presence of a chiral oxazaborolidinium ion (COBI) catalyst, the reaction proceeded with good yields (up to 99%) with excellent enantioselectivities (up to 99% ee).
- Kang, Byung Chul,Shin, Sung Ho,Yun, Jaesook,Ryu, Do Hyun
-
supporting information
p. 6316 - 6319
(2017/12/08)
-
- New functional chiral P-based ligands and application in ruthenium-catalyzed enantioselective transfer hydrogenation of ketones
-
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
-
p. 1739 - 1749
(2017/10/26)
-
- Asymmetric Transfer Hydrogenation of Ketones Using New Iron(II) (P-NH-N-P′) Catalysts: Changing the Steric and Electronic Properties at Phosphorus P′
-
The asymmetric transfer hydrogenation (ATH) of ketones is an efficient method for producing enantio-enriched alcohols which are used as intermediates in a variety of industrial processes. Here we report the synthesis of new iron ATH precatalysts (S,S)-[FeBr(CO)(Ph2PCH2CH2NHCHPhCHPhNC=CHCH2PR′2)][BPh4] (R′=Et, and ortho-tolyl (o-Tol)) where one of the phosphine groups is modified with small alkyl and large aryl substituents to probe the effect of this change on the activity and selectivity of the catalytic system. A simple reversible equilibrium kinetic model is used to obtain the initial TOF and the inherent enantioselectivity S=kR/kS of these catalysts along with those for the previously reported catalysts with R′=Ph and Cy for the ATH of acetophenone. With an increase in the size of the PR′2 group, the TOF goes through a maximum at PPh2 while the S value goes through a maximum of 510 at R′=Cy. The complex with R′=o-Tol starts with a high S value of 200 but is rapidly changed to a second catalyst with an S value of 28. For the reduction of acetophenone to (R)-1-phenylethanol, turnover numbers of up to 5200 and ee up to 98 % were achieved. The chemotherapeutic pharmaceutical precursor (R)-(3′,5′-bis(trifluoromethyl))-1-phenylethanol is synthesized in up to 95 % ee. Several other alcohols can be prepared in greater than 90 % ee by choosing the precatalyst with the correctly matched steric properties. A hydride complex derived from the catalyst with R′=Cy is characterized by NMR spectroscopy. It is proposed that low concentration trans-hydride carbonyl complexes with the FeH parallel to the NH of the ligand are the active catalysts in all of these systems.
- Smith, Samantha A. M.,Prokopchuk, Demyan E.,Morris, Robert H.
-
p. 1204 - 1215
(2017/09/06)
-
- 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
-
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
-
-
- Enantioselective transfer hydrogenation of various ketones with novel efficient iridium(III) ferrocenyl-phosphinite catalysts
-
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
-
p. 120 - 128
(2016/07/13)
-
- Iron(II)/(NH)2P2 Macrocycles: Modular, Highly Enantioselective Transfer Hydrogenation Catalysts
-
A generalized protocol for the synthesis of chiral (NH)2P2 macrocycles allows changing the linker between the phosphines and gives access to a family of such ligands, as demonstrated for the propane-1,3-diyl analogue. The corresponding complexes based on earth-abundant and nontoxic iron were applied as catalysts in the asymmetric transfer hydrogenation of polar double bonds. Thanks to the ligand modularity and to the use of tunable isonitriles as ancillary ligands, the catalyst system can be individually optimized for each substrate to give high enantioselectivity (up to 99.9% conversion and 99.6% ee, TOF up to >3950 h-1) for a broad scope of 26 substrates.
- Bigler, Raphael,Huber, Raffael,St?ckli, Marco,Mezzetti, Antonio
-
p. 6455 - 6464
(2016/10/18)
-
- IRON(II) CATALYSTS CONTAINING TRIDENTATE PNP LIGANDS, THEIR SYNTHESIS, AND USE THEREOF
-
The application describes catalytic materials for hydrogenation or asymmetric hydrogenation. In particular, the application describes iron(ll) complexes containing tridentate diphosphine PNP ligands useful for catalytic hydrogenation.
- -
-
Paragraph 0263
(2016/11/28)
-
- An unsymmetrical iron catalyst for the asymmetric transfer hydrogenation of ketones
-
A new iron(II)(Ph2P-NH-N-PCy2) complex with a dicyclohexylphosphino group trans to the NH group was found to catalyze the asymmetric transfer hydrogenation of a variety of ketones with high enantioselectivity.
- Smith, Samantha A.M.,Morris, Robert H.
-
supporting information
p. 1775 - 1779
(2015/06/16)
-
- Iron(II) complexes containing unsymmetrical P-N-P′ pincer ligands for the catalytic asymmetric hydrogenation of ketones and imines
-
After their treatment with LiAlH4 and then alcohol, new iron dicarbonyl complexes mer-trans-[Fe(Br)(CO)2(P-CH=N-P′)][BF 4] (where P-CH=N-P′ = R2PCH2CH=NCH 2CH2PPh2 and R = Cy or iPr or P-CH=N-P′ = (S,S)- Cy2PCH2CH=NCH(Me)CH(Ph)PPh2) are catalysts for the hydrogenation of ketones in THF solvent with added KOtBu at 50 C and 5 atm H2. Complexes with R = Ph are not active. With the enantiopure complex, alcohols are produced with an enantiomeric excess of up to 85% (S) at TOF up to 2000 h-1, TON of up to 5000, for a range of ketones. An activated imine is hydrogenated to the amine in 90% ee at a TOF 20 h-1and TON 99. This is a significant advance in asymmetric pressure hydrogenation using iron. The complexes are prepared in two steps: (1) a one-pot reaction of phosphonium dimers ([cyclo-(PR2CH2CH(OH) -)2][Br]2), KOtBu, FeBr2, and Ph2PCH2CH2NH2 (or (S,S)-Ph 2PCH(Ph)CH(Me)NH2 for the enantiopure complex) in THF under a CO atmosphere to produce the complexes cis- and trans-[Fe(Br) 2(CO)(P-CH=N-P′)]; (2) the reaction of these with AgBF 4 under CO(g) to afford the dicarbonyl complexes in high yield (50-90%). NMR and DFT studies of the process of precatalyst activation show that the dicarbonyl complexes are converted first to hydride-aluminum hydride complexes where the imine of the P-CH=N-P′ ligand is reduced to an amide [P-CH2N-P′]- with aluminum hydrides still bound to the nitrogen. These hydride species react with alcohol to give monohydride amine iron compounds FeH(OR′)(CO)(P-CH2NH-P′), R′ = Me, CMe2Et as well as the iron(0) complex Fe(CO)2(P-CH 2NH-P′) under certain conditions.
- Lagaditis, Paraskevi O.,Sues, Peter E.,Sonnenberg, Jessica F.,Wan, Kai Yang,Lough, Alan J.,Morris, Robert H.
-
supporting information
p. 1367 - 1380
(2014/02/14)
-
- Iron catalysts containing amine(imine)diphosphine P-NH-N-P ligands catalyze both the asymmetric hydrogenation and asymmetric transfer hydrogenation of ketones
-
When activated with base, the iron(II) complexes with tetradentate amine(imine)diphosphine ligands, (S,S)-trans-[FeCl(CO)(PAr2-NH-N-PAr′2)]BF4 (1: Ar, Ar′ = Ph; 2: Ar = Ph, Ar′ = 4-MeC6H4; 3: Ar, Ar′ = 3,5-Me2C6H3), are very active for the asymmetric transfer hydrogenation (ATH) of ketones in KOtBu/2-propanol. For ATH, better enantioselectivity, but lower catalytic activity, was observed in general when using catalyst precursors with the bulkier dixylylphosphino groups compared to those with diphenylphosphino groups. The complexes were much less active for the pressure hydrogenation of ketones, where 1 and 2 produced racemic product alcohols, while 3 yielded chiral alcohols with an enantiomeric excess of up to 70% (R) at turnover frequencies up to 80 h-1 and turnover numbers of 100 for a range of ketones at 50 °C and 20 atm H2. This is a rare example of asymmetric pressure hydrogenation using an iron complex. Unlike the case of ATH, there is no effect on the rate upon the addition of KOtBu beyond the 2 equiv needed to convert the precursor complex to the active amido(ene-amido) and amine(ene-amido)hydrido forms. Both AH and ATH reactions share the same iron hydride intermediate formed by reaction of the amido(ene-amido) iron complex with either dihydrogen or 2-propanol. Kinetic studies on the H2 hydrogenation of acetophenone catalyzed by 1, activated by base in benzene, using the method of initial rates indicated that the heterolytic splitting of the dihydrogen at the amido(ene-amido) iron complex is the turnover-limiting step of the catalytic cycle for hydrogenation. For 1 in benzene at 323 K over the ranges of concentrations [1] = (2.4-4.8) × 10-4 M and [ketone] = (3.6-7.2) × 10-2 M, and of H2 pressures = 10-20 atm, the rate law is rate = k[1][H2], with k = 0.16 ± 0.01 M-1 s-1, ΔH? = 10.0 ± 0.2 kcal mol-1, and ΔS? = -31.0 ± 0.5 cal mol-1 K-1. Detailed DFT calculations also support the finding that the barrier for H2 splitting is the turnover-limiting step. The higher barrier for H2 activation compared to isopropanol activation in order to generate the active amine(ene-amido)hydrido form explains why this system is biased toward ATH over AH.
- Zuo, Weiwei,Tauer, Sebastian,Prokopchuk, Demyan E.,Morris, Robert H.
-
p. 5791 - 5801
(2015/02/19)
-
- Highly enantioselective transfer hydrogenation of ketones with chiral (NH)2P2 Macrocyclic Iron(II) complexes
-
Bis(isonitrile) iron(II) complexes bearing a C2-symmetric diamino (NH)2P2 macrocyclic ligand efficiently catalyze the hydrogenation of polar bonds of a broad scope of substrates (ketones, enones, and imines) in high yield (up to 99.5 %), excellent enantioselectivity (up to 99 % ee), and with low catalyst loading (generally 0.1 mol %). The catalyst can be easily tuned by modifying the substituents of the isonitrile ligand. Paying the iron price: Bis(isonitrile) iron(II) complexes with a C2-symmetric diamino (NH)2P2 macrocyclic ligand efficiently catalyze the hydrogenation of polar bonds of a broad scope of substrates (ketones, enones, imines) in high yield (up to 99.5 %), excellent enantioselectivity (up to 99 % ee), and with low catalyst loading (generally 0.1 mol %).
- Bigler, Raphael,Huber, Raffael,Mezzetti, Antonio
-
supporting information
p. 5171 - 5174
(2015/04/27)
-
- Amine(imine)diphosphine iron catalysts for asymmetric transfer hydrogenation of ketones and imines
-
A rational approach is needed to design hydrogenation catalysts that make use of Earth-abundant elements to replace the rare elements such as ruthenium, rhodium, and palladium that are traditionally used. Here, we validate a prior mechanistic hypothesis that partially saturated amine(imine)diphosphine ligands (P-NH-N-P) activate iron to catalyze the asymmetric reduction of the polar bonds of ketones and imines to valuable enantiopure alcohols and amines, with isopropanol as the hydrogen donor, at turnover frequencies as high as 200 per second at 28°C. We present a direct synthetic approach to enantiopure ligands of this type that takes advantage of the iron(lI) ion as a template. The catalytic mechanism is elucidated by the spectroscopic detection of iron hydride and amide intermediates.
- Zuo, Weiwei,Lough, Alan J.,Li, Young Feng,Morris, Robert H.
-
p. 1080 - 1083
(2014/01/06)
-
- IRON CATALYSTS WITH UNSYMMETRICAL PNN'P LIGANDS
-
The present invention relates to catalytic materials for hydrogenation or asymmetric hydrogenation. In particular, the invention relates to iron (II) complexes containing unsymmetrical tetradentate diphosphine (PNN'P) ligands with two different nitrogen donor groups useful for catalytic transfer hydrogenation or asymmetric transfer hydrogenation of ketones, aldehydes and imines.
- -
-
Paragraph 00210; 00204; 00205
(2014/01/07)
-
- Asymmetric transfer hydrogenation of ketones catalyzed by nickel complex with new PNO-type ligands
-
The new polydentate mixed-N, P, O chiral ligands have been synthesized by the condensation of bis(o-formylphenyl)-phenylphosphane and R-phenylglycinol in CHCl3, and fully characterized by IR, NMR and EIMS spectra. These ligands were employed with a simple Ni complex Ni(PPhs) 2Cl2 in situ as catalytic systems for asymmetric transfer hydrogenation of ketones, and the corresponding optical alcohols were obtained with up to 84% ee under mild conditions.
- Dong, Zhen Rong,Li, Yan Yun,Yu, Shen Luan,Sun, Guo Song,Gao, Jing Xing
-
scheme or table
p. 533 - 536
(2012/06/16)
-
- Screening method for the evaluation of asymmetric catalysts for the reduction of aliphatic ketones
-
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
-
supporting information; experimental part
p. 1485 - 1489
(2011/05/16)
-
- Copper-Catalyzed enantioselective hydrosilylation of ketones by using monodentate binaphthophosphepine ligands
-
"Chemical Equation Presented" No base required: The first copper-catalyzed asymmetric hydrosilylation of carbonyl compounds by using monodentate binaphthophosphepine ligands is presented. After optimization of the reaction parameters, high yields and enantioselectivities (up to 96 % ee) for a broad range of aryl alkyl, cyclic, heterocyclic and aliphatic ketones are achieved without a base.
- Junge, Kathrin,Wendt, Bianca,Addis, Daniele,Zhou, Shaolin,Das, Shoubhik,Beller, Matthias
-
experimental part
p. 68 - 73
(2010/03/03)
-
- Asymmetric hydrogenation of ketones catalyzed by a ruthenium(ii)-indan- ambox complex
-
(S,R)-Indan-ambox ligand and its ruthenium(ii) complex have been prepared and successfully applied to asymmetric hydrogenation of prochiral simple ketones. A wide range of unfunctionalized ketones are reduced by Ru(ii)-indan-ambox catalyst with excellent enantioselectivities (up to 97% ee).
- Li, Wei,Hou, Guohua,Wang, Chunjiang,Jiang, Yutong,Zhang, Xumu
-
supporting information; experimental part
p. 3979 - 3981
(2010/07/14)
-
- Chiral nanoscale metal-organic tetrahedral cages: Diastereo-selective self-assembly and enantioselective separation
-
(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
-
supporting information; experimental part
p. 4121 - 4124
(2010/08/07)
-
- Iron(II) complexes for the efficient catalytic asymmetric transfer hydrogenation of ketones
-
Iron(II) carbonyl compounds of the type trans-[Fe(NCMe)(CO)(P-N-N-P)] [BF4]2 bearing the ethylenediamine-derived diiminodiphosphine ligands (R,R)- or (5,5)-1,2-diphenyl-1,2-diaminoethane were synthesized and characterized, including by their crystal structures. The new complexes are suitable precatalysts for the transfer hydrogenation of ketones at room temperature, giving turnover frequencies of up to 2600 h-1 with low catalyst loadings (0.025-0.17%). Screening experiments showed that the precatalysts are able to produce alcohols from a wide range of simple ketones. For sterically demanding prochiral ketones, excellent enantioselectivities were obtained (up to 96% ee).
- Meyer, Nils,Lough, Alan J.,Morris, Robert H.
-
scheme or table
p. 5605 - 5610
(2010/02/28)
-
- Mild and practical reductions of prochiral ketones to chiral alcohols using the chiral boronic ester TarB-H
-
Chiral alcohols are prepared under mild conditions in high enantiomeric excesses using the tartaric acid derived chiral boronic ester TarB-H. The phenylboronic acid was quantitatively recovered and recycled using a simple extraction with sodium hydroxide and diethyl ether. Aromatic and aliphatic secondary alcohols were prepared in up to 99% ee. Georg Thieme Verlag Stuttgart.
- Eagon, Scott,Kim, Jinsoo,Singaram, Bakthan
-
experimental part
p. 3874 - 3876
(2009/06/18)
-
- 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
-
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
-
experimental part
p. 9992 - 9998
(2009/04/11)
-
- 9-Borabicyclo[3.3.2]decanes and the asymmetric hydroboration of 1,1-disubstituted alkenes
-
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.
-
supporting information; scheme or table
p. 9218 - 9219
(2009/02/02)
-
- Self-assembly of a homochiral nanoscale metallacycle from a metallosalen complex for enantioselective separation
-
(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
-
p. 1245 - 1249
(2008/12/23)
-
- Asymmetric reductions using the chiral boronic ester TarB-H: a practical and inexpensive procedure for synthesizing chiral alcohols
-
Chiral alcohols are prepared in high enantiomeric excesses using an inexpensive and easily synthesized tartaric acid derived boronic ester (TarB-H) with sodium borohydride. The phenylboronic acid could be recovered quantitatively using a simple extraction with sodium hydroxide and diethyl ether. The optimized TarB-H system was used to reduce aromatic and aliphatic ketones in an open flask to chiral alcohols with enantiomeric excesses up to 99%.
- Eagon, Scott,Kim, Jinsoo,Yan, Katie,Haddenham, Dustin,Singaram, Bakthan
-
p. 9025 - 9029
(2008/03/18)
-
- Highly enantioselective addition of Me2Zn to aldehydes catalyzed by ClCr(Salen)
-
High enantiomeric excesses are obtained in the addition of Me2Zn catalyzed by commercially available ClCr(Salen). Broad scope, simple procedure, room temperature, low catalyst loading are the characteristics of this new enantioselective process, which uses the rather unreactive Me2Zn. Enantiomeric excesses in the range of 71-99% are obtained with all the aldehydes tested. Copyright
- Cozzi, Pier Giorgio,Kotrusz, Peter
-
p. 4940 - 4941
(2007/10/03)
-
- Enantioselective reduction of aliphatic ketones using NaBH4 and TarB-NO2, a chiral boronic ester
-
High enantioselectivities are obtained using a tartaric acid-derived boronic ester (TarB-NO2) in combination with NaBH4 for the asymmetric reduction of aliphatic ketones. The resulting alcohols are obtained in enantiomeric excesses ranging from 56% to 94%.
- Kim, Jinsoo,Singaram, Bakthan
-
p. 3901 - 3903
(2007/10/03)
-
- Synthesis of dendrimer-supported prolinols and their application in enantioselective reduction of ketones
-
Optically active dendritic amino alcohols were synthesized and applied to catalyze the enantioselective borane reduction of various ketones with good yield and high enantiomeric excesses. Georg Thieme Verlag Stuttgart.
- Wang, Guang-Yin,Liu, Xin-Yuan,Zhao, Gang
-
p. 1150 - 1154
(2007/10/03)
-
- Designing the "Search pathway" in the development of a new class of highly efficient stereoselective hydrosilylation catalysts
-
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.
-
p. 2862 - 2873
(2007/10/03)
-
- Asymmetric transesterification of secondary alcohols catalyzed by feruloyl esterase from Humicola insolens
-
A new asymmetric transesterification of secondary alcohols catalyzed by feruloyl esterase from Humicola insolens has been found. Although alcohols are not the natural substrates for this enzyme, a high R enantioselectivity was observed. Stereochemical studies showed that variations in substrate structure lead to strong variations in enantioselectivity. The highest enantioselectivities are obtained when the β-carbon of the secondary alcohol is tertiary or quaternary.
- Hatzakis, Nikos S.,Smonou, Ioulia
-
p. 325 - 337
(2007/10/03)
-