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Wolfgang Lindner - One of the best experts on this subject based on the ideXlab platform.
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liquid chromatographic resolution of natural and racemic Cinchona Alkaloid analogues using strong cation and zwitterion ion exchange type stationary phases qualitative evaluation of stationary phase characteristics and mobile phase effects on stereos
Journal of Chromatography A, 2020Co-Authors: Attila Bajtai, Antal Peter, Istvan Ilisz, Wolfgang LindnerAbstract:Liquid chromatographic (LC) and subcritical fluid chromatographic (SFC) resolution of the basic natural and synthetic Cinchona Alkaloid analogues has been studied. Focus has been placed on the employment of four enantiomerically structured chiral strong cation-exchangers and four chiral diastereoisomeric Cinchona Alkaloid and cyclohexyl aminosulfonic acid-based zwitterionic ion-exchangers. Except for the novel, recently synthesized racemic quinine the other investigated pairs of basic analytes are diastereomeric, but often called "pseudoenantiomeric" compounds of quinine and quinidine, cinchonidine and cinchonine, 9‑epi‑quinine and 9‑epi‑quinidine. As expected, the elution order of the resolved racemic quinine was reversed for all the eight investigated enantiomeric and (pseudo)enantiomeric pairs of chiral stationary phases, whereas this was not necessarily the case for the diastereomeric pairs of the Cinchona Alkaloid related analytes. Varying the type and composition of the protic (methanol) and non-protic (acetonitrile) but polar bulk solvents in combination with organic salt additives in the mobile phase the overall retention and stereoselectivity characteristics could be triggered, leading to well performing LC and SFC systems. Thus the retention behavior of the basic analytes on both the chiral cation-exchangers and the diastereomeric zwitterionic ion-exchangers, used as cation-exchangers, could be described by the stoichiometric displacement model related to the counter-ion effect of the mobile phase additives. In addition, it became obvious that the non-protic acetonitrile compared to methanol as bulk solvent lead to a significant increase in retention, which can be associated with an increased electrostatic interaction of the charged sites due to a smaller solvation shell of the solvated cationic and anionic species. Based on the chromatographic results of the systematically selected chiral analytes and stationary phases attempts were undertaken to interpret qualitatively the observed stereoselectivity phenomena.
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electrostatic attraction repulsion model with Cinchona Alkaloid based zwitterionic chiral stationary phases exemplified for zwitterionic analytes
Analytica Chimica Acta, 2019Co-Authors: Vebi Mimini, Federica Ianni, Francesca Marini, Hubert Hettegger, Roccaldo Sardella, Wolfgang LindnerAbstract:Abstract In the present paper, we demonstrated that Cinchona Alkaloid cyclohexyl sulfonic acid-based zwitterionic chiral selectors (SOs) and the respective chiral stationary phases (CSPs) can be successfully employed for the enantioseparation of underivatized thus zwitterionic amino acids (the selectands, SAs) even in the absence of ionic additives in the eluent, generally used as displacer counter-ions in ion exchange chromatography. Therefore, we provided evidence that cooperative “intramolecular and intermolecular counter-ion effects” of the zwitterionic SO moiety and the zwitterionic SAs can be sufficient to modulate alone the retention characteristics without a loss of stereoselectivity. Four fully constrained β-amino acids were used as target compounds for this study. The analyses were carried out with either neat methanol, acetonitrile, water or their binary hydro-organic mixtures. A U-shaped retention profile was observed both with methanol- and acetonitrile-based eluents. Except a few cases, enantioselectivity experienced a remarkable amelioration at the “balanced region” of a buffer free hydroorganic mobile phase composition. At “the bottom” of the U-shaped curve, high α- and resolution values could be reached with most of the screened mobile phases. An electrostatically driven “attraction-repulsion model” was postulated to explain the very favourable characteristic of the two studied zwitterion-type CSPs for the retention and enantiomer separation of zwitterionic analytes.
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dedicated comparisons of diverse polysaccharide and zwitterionic Cinchona Alkaloid based chiral stationary phases probed with basic and ampholytic indole analogs in liquid and subcritical fluid chromatography mode
Journal of Chromatography A, 2018Co-Authors: Attila Bajtai, Wolfgang Lindner, Gyula Lajko, Istvan Ilisz, Ferenc Fulop, Istvan Szatmari, Antal PeterAbstract:Abstract Normal phase (NP) high-performance liquid and sub- and supercritical fluid chromatographic (both acronymed as SFC) methods have been developed for the enantiomer separation of three basic and three ampholytic structurally related C-3-substituted indole analogs on seven non-ionic (neutral) polysaccharide-based and two chemically entirely different zwitterionic Cinchona Alkaloid- and sulfonic acid-based chiral stationary phases (CSPs). In a systematic fashion the effect of the composition of the mobile phase, the nature of the alcohol and amine additives on the retention characteristics and enantioselectivity of the ionizable analytes were investigated. On all studied polysaccharide-based CSPs the three ampholytes remained unretained in NP-LC mode, while they were nicely retained and resolved in SFC mode. These unexpected results underline a specific property of liquid CO2 as bulk solvent in combination with alcohols as co-solvents and amine additives thus creating an environment around the chiral selector sites which support the retention of ampholytes. The zwitterionic CSPs worked equally well for the resolution of the basic and ampholytic analytes using a polar ionic mobile phase in both LC and SFC modes. Results acquired by studying the effect of temperature were used to calculate the changes in standard enthalpy Δ(ΔH°), entropy Δ(ΔS°), and free energy Δ(ΔG°) applying van't Hoff plots. The values of the thermodynamic parameters depended on the nature of selectors, the structure of analytes and the properties of the mobile phases. On polysaccharide-based CSPs and columns operated in NP-LC mode enthalpically-, whereas in SFC mode both enthalpically- and entropically-driven enantiomer separations were observed.
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effects of n methylation and amidination of cyclic β amino acids on enantioselectivity and retention characteristics using Cinchona Alkaloid and sulfonic acid based chiral zwitterionic stationary phases
Journal of Chromatography A, 2018Co-Authors: Timea Orosz, Wolfgang Lindner, Istvan Ilisz, Ferenc Fulop, Enikő Forro, Antal PeterAbstract:Abstract In the present work the effects of N-methylation and N-amidination of ampholytic cyclic β-amino acids on their retention and enantioseparation characteristics on Cinchona Alkaloid- and sulfonic acid-based zwitterionic chiral selectors, namely Chiralpak ZWIX(+)™ and ZWIX(−)™ columns are described. In a polar-ionic mobile phase, a double ion-pairing interaction mechanism takes place between the charged sites of the chiral analytes (the selectands) and the chiral selector moieties. As a support to correlate the chromatographic results with the structural details of the analytes, pKa values and van der Waals volumes of the substituted amino groups were calculated. In order to ensure better understanding of the mechanistic details of the chromatographic system the composition of the bulk solvent, the role of acid base additives, the concentration of the counter-ions, temperature and the structures of the ampholytic analytes have been investigated. Applying N-Fmoc protection, the ampholytic character of the analytes diminished, leading to a marked loss of retention. In the temperature range studied (5–40 °C) thermodynamic parameters, such as the difference in the standard enthalpy change Δ(ΔH°), entropy Δ(ΔS) and Gibbs energy Δ(ΔG°) were calculated from linear van’t Hoff plots derived from the ln α vs. 1/T curves. The values of the thermodynamic parameters depended on the structures of the chiral selectors applied and the analytes studied.
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application of Cinchona Alkaloid based zwitterionic chiral stationary phases in supercritical fluid chromatography for the enantioseparation of nα protected proteinogenic amino acids
Journal of Chromatography A, 2015Co-Authors: Gyula Lajko, Wolfgang Lindner, Istvan Ilisz, Gabor Toth, Ferenc Fulop, Antal PeterAbstract:Abstract Stereoselective supercritical fluid chromatographic separations of the enantiomers of a large set of Nα-Fmoc proteinogenic amino acids were carried out on the recently developed Cinchona Alkaloid-based zwitterionic chiral stationary phases Chiralpak ZWIX(+)™ and ZWIX(−)™ with protic solvents as co-solvents. The effects of the mobile phase composition, the natures and concentrations of the acid or base additives, the co- and counter-ions and temperature on the separations were investigated. The retention time in most cases slightly increased, while the separation factor decreased with increasing temperature. The changes in standard enthalpy, Δ(ΔH°), entropy, Δ(ΔS°), and free energy, Δ(ΔG°), were calculated from the linear van’t Hoff plots derived from the ln α vs 1/T curves in the studied temperature range (20–60 °C). The values of the thermodynamic parameters depended on the natures of the selectors and the structures of the analytes. On both ZWIX(+)™ and ZWIX(−)™ columns, enthalpically-driven separations were observed. The elution sequence was determined in all cases and was observed to be opposite on ZWIX(+)™ and ZWIX(−)™ which acted for the presented applications as chiral anion exchanger.
Antal Peter - One of the best experts on this subject based on the ideXlab platform.
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liquid chromatographic resolution of natural and racemic Cinchona Alkaloid analogues using strong cation and zwitterion ion exchange type stationary phases qualitative evaluation of stationary phase characteristics and mobile phase effects on stereos
Journal of Chromatography A, 2020Co-Authors: Attila Bajtai, Antal Peter, Istvan Ilisz, Wolfgang LindnerAbstract:Liquid chromatographic (LC) and subcritical fluid chromatographic (SFC) resolution of the basic natural and synthetic Cinchona Alkaloid analogues has been studied. Focus has been placed on the employment of four enantiomerically structured chiral strong cation-exchangers and four chiral diastereoisomeric Cinchona Alkaloid and cyclohexyl aminosulfonic acid-based zwitterionic ion-exchangers. Except for the novel, recently synthesized racemic quinine the other investigated pairs of basic analytes are diastereomeric, but often called "pseudoenantiomeric" compounds of quinine and quinidine, cinchonidine and cinchonine, 9‑epi‑quinine and 9‑epi‑quinidine. As expected, the elution order of the resolved racemic quinine was reversed for all the eight investigated enantiomeric and (pseudo)enantiomeric pairs of chiral stationary phases, whereas this was not necessarily the case for the diastereomeric pairs of the Cinchona Alkaloid related analytes. Varying the type and composition of the protic (methanol) and non-protic (acetonitrile) but polar bulk solvents in combination with organic salt additives in the mobile phase the overall retention and stereoselectivity characteristics could be triggered, leading to well performing LC and SFC systems. Thus the retention behavior of the basic analytes on both the chiral cation-exchangers and the diastereomeric zwitterionic ion-exchangers, used as cation-exchangers, could be described by the stoichiometric displacement model related to the counter-ion effect of the mobile phase additives. In addition, it became obvious that the non-protic acetonitrile compared to methanol as bulk solvent lead to a significant increase in retention, which can be associated with an increased electrostatic interaction of the charged sites due to a smaller solvation shell of the solvated cationic and anionic species. Based on the chromatographic results of the systematically selected chiral analytes and stationary phases attempts were undertaken to interpret qualitatively the observed stereoselectivity phenomena.
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dedicated comparisons of diverse polysaccharide and zwitterionic Cinchona Alkaloid based chiral stationary phases probed with basic and ampholytic indole analogs in liquid and subcritical fluid chromatography mode
Journal of Chromatography A, 2018Co-Authors: Attila Bajtai, Wolfgang Lindner, Gyula Lajko, Istvan Ilisz, Ferenc Fulop, Istvan Szatmari, Antal PeterAbstract:Abstract Normal phase (NP) high-performance liquid and sub- and supercritical fluid chromatographic (both acronymed as SFC) methods have been developed for the enantiomer separation of three basic and three ampholytic structurally related C-3-substituted indole analogs on seven non-ionic (neutral) polysaccharide-based and two chemically entirely different zwitterionic Cinchona Alkaloid- and sulfonic acid-based chiral stationary phases (CSPs). In a systematic fashion the effect of the composition of the mobile phase, the nature of the alcohol and amine additives on the retention characteristics and enantioselectivity of the ionizable analytes were investigated. On all studied polysaccharide-based CSPs the three ampholytes remained unretained in NP-LC mode, while they were nicely retained and resolved in SFC mode. These unexpected results underline a specific property of liquid CO2 as bulk solvent in combination with alcohols as co-solvents and amine additives thus creating an environment around the chiral selector sites which support the retention of ampholytes. The zwitterionic CSPs worked equally well for the resolution of the basic and ampholytic analytes using a polar ionic mobile phase in both LC and SFC modes. Results acquired by studying the effect of temperature were used to calculate the changes in standard enthalpy Δ(ΔH°), entropy Δ(ΔS°), and free energy Δ(ΔG°) applying van't Hoff plots. The values of the thermodynamic parameters depended on the nature of selectors, the structure of analytes and the properties of the mobile phases. On polysaccharide-based CSPs and columns operated in NP-LC mode enthalpically-, whereas in SFC mode both enthalpically- and entropically-driven enantiomer separations were observed.
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effects of n methylation and amidination of cyclic β amino acids on enantioselectivity and retention characteristics using Cinchona Alkaloid and sulfonic acid based chiral zwitterionic stationary phases
Journal of Chromatography A, 2018Co-Authors: Timea Orosz, Wolfgang Lindner, Istvan Ilisz, Ferenc Fulop, Enikő Forro, Antal PeterAbstract:Abstract In the present work the effects of N-methylation and N-amidination of ampholytic cyclic β-amino acids on their retention and enantioseparation characteristics on Cinchona Alkaloid- and sulfonic acid-based zwitterionic chiral selectors, namely Chiralpak ZWIX(+)™ and ZWIX(−)™ columns are described. In a polar-ionic mobile phase, a double ion-pairing interaction mechanism takes place between the charged sites of the chiral analytes (the selectands) and the chiral selector moieties. As a support to correlate the chromatographic results with the structural details of the analytes, pKa values and van der Waals volumes of the substituted amino groups were calculated. In order to ensure better understanding of the mechanistic details of the chromatographic system the composition of the bulk solvent, the role of acid base additives, the concentration of the counter-ions, temperature and the structures of the ampholytic analytes have been investigated. Applying N-Fmoc protection, the ampholytic character of the analytes diminished, leading to a marked loss of retention. In the temperature range studied (5–40 °C) thermodynamic parameters, such as the difference in the standard enthalpy change Δ(ΔH°), entropy Δ(ΔS) and Gibbs energy Δ(ΔG°) were calculated from linear van’t Hoff plots derived from the ln α vs. 1/T curves. The values of the thermodynamic parameters depended on the structures of the chiral selectors applied and the analytes studied.
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application of Cinchona Alkaloid based zwitterionic chiral stationary phases in supercritical fluid chromatography for the enantioseparation of nα protected proteinogenic amino acids
Journal of Chromatography A, 2015Co-Authors: Gyula Lajko, Wolfgang Lindner, Istvan Ilisz, Gabor Toth, Ferenc Fulop, Antal PeterAbstract:Abstract Stereoselective supercritical fluid chromatographic separations of the enantiomers of a large set of Nα-Fmoc proteinogenic amino acids were carried out on the recently developed Cinchona Alkaloid-based zwitterionic chiral stationary phases Chiralpak ZWIX(+)™ and ZWIX(−)™ with protic solvents as co-solvents. The effects of the mobile phase composition, the natures and concentrations of the acid or base additives, the co- and counter-ions and temperature on the separations were investigated. The retention time in most cases slightly increased, while the separation factor decreased with increasing temperature. The changes in standard enthalpy, Δ(ΔH°), entropy, Δ(ΔS°), and free energy, Δ(ΔG°), were calculated from the linear van’t Hoff plots derived from the ln α vs 1/T curves in the studied temperature range (20–60 °C). The values of the thermodynamic parameters depended on the natures of the selectors and the structures of the analytes. On both ZWIX(+)™ and ZWIX(−)™ columns, enthalpically-driven separations were observed. The elution sequence was determined in all cases and was observed to be opposite on ZWIX(+)™ and ZWIX(−)™ which acted for the presented applications as chiral anion exchanger.
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effect of mobile phase composition on the liquid chromatographic enantioseparation of bulky monoterpene based β amino acids by applying chiral stationary phases based on Cinchona Alkaloid
IEEE Journal of Solid-state Circuits, 2014Co-Authors: Zoltan Pataj, Wolfgang Lindner, Istvan Ilisz, Ferenc Fulop, Zsanett Gecse, Zsolt Szakonyi, Antal PeterAbstract:Stereoselective HPLC separations of five sterically constrained monoterpene-based 2-aminocarboxylic acid enantiomers were carried out by using the newly developed zwitterionic chiral stationary phases Chiralpak ZWIX(+)™ and ZWIX(-)™ based on Cinchona Alkaloid. In order to optimize the retention and enantioselectivity parameters, the ratio of the different organic solvents in the mobile phase and the nature of the acid and base additives (counter- and co-ions) were systematically varied. The effects of structure variants of the analytes on the resolution were investigated. The elution sequence was determined in all cases and observed to be opposite on ZWIX(+)™ and ZWIX(-)™.
Min Shi - One of the best experts on this subject based on the ideXlab platform.
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Cinchona Alkaloid squaramide catalyzed asymmetric michael addition of α aryl isocyanoacetates to β trifluoromethylated enones and its applications in the synthesis of chiral β trifluoromethylated pyrrolines
Journal of Organic Chemistry, 2015Co-Authors: Mei-xin Zhao, Huikai Zhu, Tonglei Dai, Min ShiAbstract:Cinchona Alkaloid squaramide can effectively catalyze the asymmetric Michael addition of α-aryl isocyanoacetates to β-trifluoromethylated enones, affording the corresponding adducts with an adjacent chiral tertiary carbon center bearing a CF3 group and a quaternary carbon center in moderate to good yields along with excellent stereoselectivities. The adduct can be easily transformed into biologically attractive chiral β-trifluoromethylated pyrroline carboxylate in high yield via an isocyano group hydrolysis/cyclization/dehydration cascade reaction by treating with acid. The one-pot enantioselective Michael addition/isocyano group hydrolysis/cyclization/dehydration sequential protocol has also been investigated.
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Cinchona Alkaloid squaramide agoac cooperatively catalyzed diastereo and enantioselective mannich cyclization cascade reaction of isocyanoacetates and cyclic trifluoromethyl ketimines
Organic Letters, 2014Co-Authors: Mei-xin Zhao, Rong-hui Jiang, Min ShiAbstract:An efficient diastereo- and enantioselective Mannich-type/cyclization cascade reaction of α-substituted isocyanoacetates and cyclic trifluoromethyl ketimines cooperatively catalyzed by Cinchona Alkaloid-derived multi-hydrogen-bonding donor squaramide and AgOAc has been investigated, affording the optically active trifluoromethyl-substituted tetrahydroimidazo[1,5-c]quinazoline derivatives in excellent yields (up to 99%) and good to excellent stereoselectivities (up to >15:1 dr, up to 98% ee) under mild conditions.
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Cinchona Alkaloid Squaramide/AgOAc Cooperatively Catalyzed Diastereo- and Enantioselective Mannich/Cyclization Cascade Reaction of Isocyanoacetates and Cyclic Trifluoromethyl Ketimines
2014Co-Authors: Mei-xin Zhao, Rong-hui Jiang, Min ShiAbstract:An efficient diastereo- and enantioselective Mannich-type/cyclization cascade reaction of α-substituted isocyanoacetates and cyclic trifluoromethyl ketimines cooperatively catalyzed by Cinchona Alkaloid-derived multi-hydrogen-bonding donor squaramide and AgOAc has been investigated, affording the optically active trifluoromethyl-substituted tetrahydroimidazo[1,5-c]quinazoline derivatives in excellent yields (up to 99%) and good to excellent stereoselectivities (up to >15:1 dr, up to 98% ee) under mild conditions
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Cinchona Alkaloid squaramide catalyzed enantioselective hydrazination cyclization cascade reaction of α isocyanoacetates and azodicarboxylates synthesis of optically active 1 2 4 triazolines
Journal of Organic Chemistry, 2013Co-Authors: Mei-xin Zhao, Hui Yang, Hao Zhou, Min ShiAbstract:An efficient enantioselective hydrazination/cyclization cascade reaction of α-substituted isocyanoacetates to azodicarboxylates catalyzed by Cinchona Alkaloid derived squaramide catalysts has been investigated, affording the optically active 1,2,4-triazolines in excellent yields (up to 99%) and good to excellent enantioselectivities (up to 97% ee) under mild conditions.
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Cinchona Alkaloid Squaramide Catalyzed Enantioselective Hydrazination/Cyclization Cascade Reaction of α‑Isocyanoacetates and Azodicarboxylates: Synthesis of Optically Active 1,2,4-Triazolines
2013Co-Authors: Mei-xin Zhao, Hui Yang, Hao Zhou, Min ShiAbstract:An efficient enantioselective hydrazination/cyclization cascade reaction of α-substituted isocyanoacetates to azodicarboxylates catalyzed by Cinchona Alkaloid derived squaramide catalysts has been investigated, affording the optically active 1,2,4-triazolines in excellent yields (up to 99%) and good to excellent enantioselectivities (up to 97% ee) under mild conditions
Shuichi Nakamura - One of the best experts on this subject based on the ideXlab platform.
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enantioselective oxidative ring opening reaction of aziridines with α nitroesters using Cinchona Alkaloid amide nickel ii catalysts
Organic Letters, 2017Co-Authors: Noriyuki Shiomi, Yasuhiro Funahashi, Keisuke Yamamoto, Kazuma Nagasaki, Tsubasa Hatanaka, Shuichi NakamuraAbstract:The enantioselective oxidative ring-opening reaction of aziridines with α-nitroacetates has been developed. Good yields and enantioselectivity were observed for the reaction of various aziridines using a novel Cinchona Alkaloid amide/NiBr2 catalyst. Both enantiomers of products could be obtained by using pseudoenantiomeric chiral catalysts. This process offers an efficient route for the synthesis of α-aminoketones.
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enantioselective construction of imidazolines having vicinal tetra substituted stereocenters by direct mannich reaction of α substituted α isocyanoacetates with ketimines
Chemical Communications, 2016Co-Authors: Shuichi Nakamura, Ryota Yamaji, Masaru IwanagaAbstract:The catalytic Mannich reaction of α-substituted α-isocyanoacetates with ketimines has been investigated. A variety of imidazolines containing congested vicinal tetra-substituted stereocenters were obtained in excellent yields with high diastereo- and enantioselectivity using Cinchona Alkaloid amide/Ni(ii) and base catalysts.
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organocatalytic enantioselective conjugate addition of malonic acid half thioesters to coumarin 3 carboxylic acids using n heteroarenesulfonyl Cinchona Alkaloid amides
Advanced Synthesis & Catalysis, 2016Co-Authors: Shuichi Nakamura, Masahide Sano, Tsubasa Hatanaka, Ayaka Toda, Yasuhiro FunahashiAbstract:We disclose herein an efficient enantioselective conjugate addition reaction between coumarin-3-carboxylic acids and malonic acid half thioesters (MAHTs). The reaction was catalyzed by N-heteroarenesulfonyl Cinchona Alkaloid amides to afford double-decarboxylative conjugate addition products in good yield with high enantioselectivity. The reaction of various coumarin-3-carboxylic acids with MAHTs gave products in high yield with high enantioselectivity.
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direct enantioselective vinylogous mannich reaction of ketimines with γ butenolide by using Cinchona Alkaloid amide zinc ii catalysts
Chemistry: A European Journal, 2015Co-Authors: Shuichi Nakamura, Ryota Yamaji, Masashi HayashiAbstract:A direct enantioselective vinylogous Mannich reaction of ketimines with γ-butenolide has been developed. Good yields and enantioselectivities were observed for the reaction of various ketimines by using a Cinchona Alkaloid amide/Zn(OTf)2 catalyst and Et3N. Both enantiomers of the products could be obtained by using pseudoenantiomeric chiral catalysts.
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organocatalytic enantioselective decarboxylative reaction of malonic acid half thioesters with cyclic n sulfonyl ketimines by using n heteroarenesulfonyl Cinchona Alkaloid amides
Chemistry: A European Journal, 2015Co-Authors: Shuichi Nakamura, Masahide Sano, Daisuke Nakane, Ayaka Toda, Hideki MasudaAbstract:The organocatalytic enantioselective decarboxylative Mannich reaction of malonic acid half thioesters (MAHTs) with cyclic N-sulfonyl ketimines by using N-heteroarenesulfonyl Cinchona Alkaloid amides afforded products with high enantioselectivity. Both enantiomers of the products could be obtained by using pseudoenantiomeric chiral catalysts. The reaction proceeds through a nucleophilic addition of the MAHTs to the ketimines prior to decarboxylation.
Yian Shi - One of the best experts on this subject based on the ideXlab platform.
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catalytic asymmetric bromination of unfunctionalized olefins with h2o as a nucleophile
ChemInform, 2015Co-Authors: Xun Zhang, Hua Tian, Yian ShiAbstract:A dimeric Cinchona Alkaloid is used to catalyze the enantioselective bromohydroxylation of unactivated olefins, with H2O as nucleophile and N-bromobenzamide as bromine source.
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catalytic asymmetric bromination of unfunctionalized olefins with h2o as a nucleophile
Chemistry: A European Journal, 2015Co-Authors: Xun Zhang, Hua Tian, Yian ShiAbstract:The dimeric Cinchona Alkaloid (DHQD)(2)PHAL is used to catalyze an effective asymmetric bromohydroxylation of unfunctionalized olefins with H2O as nucleophile an N-bromobenzamide as a bromine source. A variety of optically active bromohydrins are formed with up to 88%ee.