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Search for "enantiomeric excess" in Full Text gives 180 result(s) in Beilstein Journal of Organic Chemistry.

Synthesis of tryptophan-dehydrobutyrine diketopiperazine and biological activity of hangtaimycin and its co-metabolites

  • Houchao Xu,
  • Anne Wochele,
  • Minghe Luo,
  • Gregor Schnakenburg,
  • Yuhui Sun,
  • Heike Brötz-Oesterhelt and
  • Jeroen S. Dickschat

Beilstein J. Org. Chem. 2022, 18, 1159–1165, doi:10.3762/bjoc.18.120

Graphical Abstract
  • integration, Figure 1B). Further improvement of the enantiomeric excess of 4 (90% ee, Figure 1C) was possible by performing the elimination reaction with 14 and KH and 18-crown-6 under ice cooling. This helped to suppress basic racemisation of 4, but required prolonged reaction times and gave a slightly
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Published 07 Sep 2022

Anti-inflammatory aromadendrane- and cadinane-type sesquiterpenoids from the South China Sea sponge Acanthella cavernosa

  • Shou-Mao Shen,
  • Qing Yang,
  • Yi Zang,
  • Jia Li,
  • Xueting Liu and
  • Yue-Wei Guo

Beilstein J. Org. Chem. 2022, 18, 916–925, doi:10.3762/bjoc.18.91

Graphical Abstract
  • (+)-ximaocavernosin P [(+)-1]. Further, these isothiocyano-containing enantiomers were usually isolated as scalable mixture (where one enantiomer predominates) with an enantiomeric excess of ca. 80% [11]. In contrast, the two neutral cadinane-type enantiomers (4 and 5) were produced as racemic mixture (1:1 ratio
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Published 25 Jul 2022

Synthetic strategies for the preparation of γ-phostams: 1,2-azaphospholidine 2-oxides and 1,2-azaphospholine 2-oxides

  • Jiaxi Xu

Beilstein J. Org. Chem. 2022, 18, 889–915, doi:10.3762/bjoc.18.90

Graphical Abstract
  • complex showed 23% enantiomeric excess in the asymmetric borane reduction of acetophenone in THF at room temperature (Scheme 33) [58]. The reaction of 3-(phenylaminomethylene)-2-phenylamino-6-methyl-2,3-dihydro-4H-chromen-4-one (213) and diethyl phosphite at 90–100 °C generated 2-ethoxy-6-methyl-2-oxo-1
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Published 22 Jul 2022

Shift of the reaction equilibrium at high pressure in the continuous synthesis of neuraminic acid

  • Jannis A. Reich,
  • Miriam Aßmann,
  • Kristin Hölting,
  • Paul Bubenheim,
  • Jürgen Kuballa and
  • Andreas Liese

Beilstein J. Org. Chem. 2022, 18, 567–579, doi:10.3762/bjoc.18.59

Graphical Abstract
  • kinetics [16][17][18], in enantiomeric excess [19], in stability [20], or in the position of the equilibrium [17][21]. State of the art for high-pressure research is the use of pressurized batch reactors [22][23]. Since continuous production and suitable reactors are receiving more attention [24], and some
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Published 20 May 2022

Bioinspired tetraamino-bisthiourea chiral macrocycles in catalyzing decarboxylative Mannich reactions

  • Hao Guo,
  • Yu-Fei Ao,
  • De-Xian Wang and
  • Qi-Qiang Wang

Beilstein J. Org. Chem. 2022, 18, 486–496, doi:10.3762/bjoc.18.51

Graphical Abstract
  • on the reaction stereoselectivity. The cyclohexanediamine-linking macrocycles M1–M4 afforded the product with overall higher enantiomeric excess (ee) (Table 1, entries 1–4). Among which the isopropyl-substituted macrocycle M3 gave the best selectivity, i.e., 42% ee. This suggested a suitable crowding
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Published 02 May 2022

The asymmetric Henry reaction as synthetic tool for the preparation of the drugs linezolid and rivaroxaban

  • Martin Vrbický,
  • Karel Macek,
  • Jaroslav Pochobradský,
  • Jan Svoboda,
  • Miloš Sedlák and
  • Pavel Drabina

Beilstein J. Org. Chem. 2022, 18, 438–445, doi:10.3762/bjoc.18.46

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  • series of 11 efficient enantioselective catalysts was tested to obtain the corresponding nitroaldol 21 in an enantiomeric excess as high as possible. Four of them based on the chiral ligands Ia, IIa, IIIa, and IV were identified as the most effective catalysts. They exhibited mutually comparable
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Published 14 Apr 2022

Organocatalytic asymmetric nitroso aldol reaction of α-substituted malonamates

  • Ekta Gupta,
  • Narendra Kumar Vaishanv,
  • Sandeep Kumar,
  • Raja Krishnan Purshottam,
  • Ruchir Kant and
  • Kishor Mohanan

Beilstein J. Org. Chem. 2022, 18, 217–224, doi:10.3762/bjoc.18.25

Graphical Abstract
  • better result furnishing the product in 90% yield and 90% enantiomeric excess (Table 1, entry 2). Further lowering of the reaction temperature did not improve the enantioselectivity and slowed down the reaction (Table 1, entries 3 and 4). Our next attempts on the improvement of enantioselectivity focused
  • , CDCl3) δ 171.5 (C), 167.0 (C), 147.1 (C), 136.5 (C), 132.1 (CH), 132.1(CH), 128.9 (CH), 128.9 (CH), 126.1 (CH), 122.2 (CH), 122.2 (CH), 121.6 (CH), 121.6 (CH), 117.4 (C), 76.8 (C), 53.5 (CH3), 17.9 (CH3) ppm. The enantiomeric excess was determined by HPLC on a Chiralpak IC column (hexane/ethanol 90:10 v
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Published 21 Feb 2022

Asymmetric organocatalytic Michael addition of cyclopentane-1,2-dione to alkylidene oxindole

  • Estelle Silm,
  • Ivar Järving and
  • Tõnis Kanger

Beilstein J. Org. Chem. 2022, 18, 167–173, doi:10.3762/bjoc.18.18

Graphical Abstract
  • inseparable diastereoisomers in 53% yield but in low enantiomeric excess for both diastereomers (Table 1, entry 1). With the quinine-derived thiourea B, the reaction was slow and the yield was very low, 12% (Table 1, entry 2). For that reason, we focused on the screening of squaramides. Squaramides were found
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Published 03 Feb 2022

Bifunctional thiourea-catalyzed asymmetric [3 + 2] annulation reactions of 2-isothiocyanato-1-indanones with barbiturate-based olefins

  • Jiang-Song Zhai and
  • Da-Ming Du

Beilstein J. Org. Chem. 2022, 18, 25–36, doi:10.3762/bjoc.18.3

Graphical Abstract
  • chromatography. The diastereoisomeric ratios (dr values) were determined by 1H NMR spectroscopy and the enantiomeric excess (ee) values were determined by HPLC analysis. Gram-scale synthesis of 3ah. Further transformation of 3ah. One-pot three-component reaction. Proposed reaction mechanism. Optimization of the
  • reactions were carried out with 1 (0.12 mmol), 2a (0.10 mmol), and catalyst (5 mol %) in solvent (1.0 mL) at room temperature for 12 h. The yields refer to the isolated products after column chromatography. The diastereoisomeric ratios (dr values) were determined by 1H NMR spectroscopy and the enantiomeric
  • excess (ee) values were determined by HPLC analysis. Substrate scope of barbiturate-based olefins. The reactions were carried out with 1a (0.12 mmol), 2 (0.10 mmol) and catalyst C4 (5 mol %) in solvent (1.0 mL) at room temperature for 12–40 h. The yields refer to isolated products after column
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Published 04 Jan 2022

Synthetic strategies toward 1,3-oxathiolane nucleoside analogues

  • Umesh P. Aher,
  • Dhananjai Srivastava,
  • Girij P. Singh and
  • Jayashree B. S

Beilstein J. Org. Chem. 2021, 17, 2680–2715, doi:10.3762/bjoc.17.182

Graphical Abstract
  • intermediate 37 was resolved using a lipase in t-BuOMe, resulting in a high enantiomeric excess. They used an enzymatic resolution of an acetoxy sulfide with a Pseudomonas fluorescens lipase to obtain compound 38. Reaction of chiral acetoxy sulfide 38 with HCl in dry ethanol induced acetate removal by
  • THF and phosphate-buffered saline (PBS). The reaction used 64 and 3q as starting materials and was stereocontrolled efficiently, providing an enantiomeric excess of about >99%. The subsequent N-glycosylation further provided enantiopure lamivudine (1). Hu et al. [60] explained that chiral HPLC and
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Published 04 Nov 2021

Solvent-free synthesis of enantioenriched β-silyl nitroalkanes under organocatalytic conditions

  • Akhil K. Dubey and
  • Raghunath Chowdhury

Beilstein J. Org. Chem. 2021, 17, 2642–2649, doi:10.3762/bjoc.17.177

Graphical Abstract
  • even with better yields while the enantiomeric excess was unperturbed. Conclusion In summary, we have outlined bifunctional squaramide-catalyzed 1,4-conjugate addition reaction of nitromethane to β-silyl α,β-unsaturated carbonyl compounds to access a series of chiral β-silyl nitroalkanes in high yields
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Published 27 Oct 2021

Enantioselective PCCP Brønsted acid-catalyzed aminalization of aldehydes

  • Martin Kamlar,
  • Robert Reiberger,
  • Martin Nigríni,
  • Ivana Císařová and
  • Jan Veselý

Beilstein J. Org. Chem. 2021, 17, 2433–2440, doi:10.3762/bjoc.17.160

Graphical Abstract
  • averaged only around 50%. In addition, the role of an electron-donating methyl group on the aromatic ring was investigated. When p-tolualdehyde (1f) was used in the cyclization reaction with anthranilamide (1a), the corresponding aminal 3f was obtained in high yield (83%) and with good enantiomeric excess
  • enantiomeric excess of 66% ee. We also increased the enantiomeric purity of 3l from 70% to 80% ee after crystallization from ethyl acetate. When anthranilamide substituted with a chlorine in the “5” position was used, the enantioselectivity of the reaction reached a value of 76% ee, and the yield of the
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Published 16 Sep 2021

Halides as versatile anions in asymmetric anion-binding organocatalysis

  • Lukas Schifferer,
  • Martin Stinglhamer,
  • Kirandeep Kaur and
  • Olga García Macheño

Beilstein J. Org. Chem. 2021, 17, 2270–2286, doi:10.3762/bjoc.17.145

Graphical Abstract
  • these types of reactions. The first thiourea-catalyzed asymmetric intermolecular reaction with N-acyliminium chlorides was then also realized by the same group in 2009. Therein, nucleophilic addition of indoles 17 to the N-acyliminium chlorides was achieved with excellent enantiomeric excess (Scheme 4b
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Published 01 Sep 2021

Asymmetric organocatalyzed synthesis of coumarin derivatives

  • Natália M. Moreira,
  • Lorena S. R. Martelli and
  • Arlene G. Corrêa

Beilstein J. Org. Chem. 2021, 17, 1952–1980, doi:10.3762/bjoc.17.128

Graphical Abstract
  • addition of cyclic 1,3‐dicarbonyl compounds, including 4-hydroxycoumarins 1, to α,β‐unsaturated enones 2 (Scheme 1). This versatile Michael reaction afforded (S)-warfarin (3a) and other Michael adducts 3 in high yields and good enantiomeric excess (ee), using (4S,5S)-4,5-diphenylimidazolidine-2-carboxylic
  • high diastereo- and enantioselectivity and moderate to excellent yields. The authors highlighted that the catalyst also contributes to cyclization, since subjecting the isolated Michael adduct to the second conditions with iodine and K2CO3 there is a decrease in yield and enantiomeric excess when
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Published 03 Aug 2021

Development of N-F fluorinating agents and their fluorinations: Historical perspective

  • Teruo Umemoto,
  • Yuhao Yang and
  • Gerald B. Hammond

Beilstein J. Org. Chem. 2021, 17, 1752–1813, doi:10.3762/bjoc.17.123

Graphical Abstract
  • -fluorosultams were stable below 100 °C. The enantioselectivities of products were examined after the fluorination of different metal enolates. In the best case a 63% yield and 70% enantiomeric excess (ee) was obtained. Even though other products gave less satisfactory outcomes, the potential of the N-F
  • showcase his methodology, they first synthesized acyclic optically active N-fluoro sulfonamides 27-7–9 (Scheme 62) and attempted the enantioselective fluorination of some enolates in 1997 [92]. However, the best result was an enantiomeric excess of 48% with a chemical yield of 53% after the enolate anion
  • )-27-6. Enantioselective fluorinations of typical enolates were then performed (Scheme 63). The (R)-27-6 reagent gave up to 79% yield and 88% enantiomeric excess in the case of 2-benzyl-α-tetralone. 1-28. (R)- and (S)-N-fluoro-3-tert-butyl-7-nitro-benzothiazine 1,1-dioxides and spiro-type analogues In
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Published 27 Jul 2021

Methodologies for the synthesis of quaternary carbon centers via hydroalkylation of unactivated olefins: twenty years of advances

  • Thiago S. Silva and
  • Fernando Coelho

Beilstein J. Org. Chem. 2021, 17, 1565–1590, doi:10.3762/bjoc.17.112

Graphical Abstract
  • -alkenyl β-ketoamides 16, in yields ranging from 74% to 94%, in excellent enantiomeric excess (up to 98% ee), and in modest to poor diastereoisomeric ratios (dr up to 70:30). The authors observed that the nature of the activator had a substantial influence on the reaction enantio- and diastereoselectivity
  • hydroalkylated product without erosion of the enantiomeric excess. Congested halides, such as 87i, were poor substrates for this transformation, and low conversions (1–10%) were observed when more sterically demanding halides were employed. Reductive atom transfer reactions Reductive atom transfer reactions
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Published 07 Jul 2021

Organocatalytic asymmetric Michael/acyl transfer reaction between α-nitroketones and 4-arylidenepyrrolidine-2,3-diones

  • Chandrakanta Parida and
  • Subhas Chandra Pan

Beilstein J. Org. Chem. 2021, 17, 1447–1452, doi:10.3762/bjoc.17.100

Graphical Abstract
  • benzoyl-transfer reaction. However, only 20% enantiomeric excess was achieved. Then, the tert-leucine-derived squaramide catalyst II was employed and here both yield and ee slightly improved. Next, we turned our attention to bifunctional thiourea catalysts [26][27] that proved to be fruitful. Thus, the
  • suitable for the reaction though a moderate enantiomeric excess was detected. Finally, the best catalyst turned out to be the pyrrolidine-containing bifunctional thiourea catalyst VII and the desired product was isolated in 80% yield with 80% ee. Then, solvent optimization was carried out to obtain better
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Published 14 Jun 2021

N-tert-Butanesulfinyl imines in the asymmetric synthesis of nitrogen-containing heterocycles

  • Joseane A. Mendes,
  • Paulo R. R. Costa,
  • Miguel Yus,
  • Francisco Foubelo and
  • Camilla D. Buarque

Beilstein J. Org. Chem. 2021, 17, 1096–1140, doi:10.3762/bjoc.17.86

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  • Grignard reagents using THF or CH2Cl2 as solvent at 40 °C. The 3-substituted dihydrobenzo[de]isoquinolinones 154 were obtained with good yield and with enantiomeric excess of 46–99%. The mechanism was explained by stereoselective addition of the Grignard reagent to the N-sulfinyl imine 153a derived from
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Published 12 May 2021

Recent advances in palladium-catalysed asymmetric 1,4–additions of arylboronic acids to conjugated enones and chromones

  • Jan Bartáček,
  • Jan Svoboda,
  • Martin Kocúrik,
  • Jaroslav Pochobradský,
  • Alexander Čegan,
  • Miloš Sedlák and
  • Jiří Váňa

Beilstein J. Org. Chem. 2021, 17, 1048–1085, doi:10.3762/bjoc.17.84

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  • intermediate, the protecting group was removed and the product was obtained in 88% yield and 80% ee. The enantiomeric excess of the obtained (S)-3-(hydroxymethyl)-3-phenyl-2-cyclopentanone could be increased by double recrystallization to up to 97% ee (Scheme 15) [4]. The catalytic system L9/Pd(TFA)2 was
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Published 10 May 2021

Prins cyclization-mediated stereoselective synthesis of tetrahydropyrans and dihydropyrans: an inspection of twenty years

  • Asha Budakoti,
  • Pradip Kumar Mondal,
  • Prachi Verma and
  • Jagadish Khamrai

Beilstein J. Org. Chem. 2021, 17, 932–963, doi:10.3762/bjoc.17.77

Graphical Abstract
  • % yield and <5% ee. The poor enantiomeric excess of the product 23 indicates that the racemization takes place during the course of the reaction. It was explained that the reason for the loss of optical purity was due to the formation of a benzylic cation, which is stabilized by the electron-rich aromatic
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Published 29 Apr 2021

Kinetics of enzyme-catalysed desymmetrisation of prochiral substrates: product enantiomeric excess is not always constant

  • Peter J. Halling

Beilstein J. Org. Chem. 2021, 17, 873–884, doi:10.3762/bjoc.17.73

Graphical Abstract
  • -pong second (ketone amination, diol esterification, desymmetrisation in the second half reaction); ping-pong first (diol ester hydrolysis) and ping-pong both (prochiral diacids). For plausible values of enzyme kinetic parameters, the product enantiomeric excess (ee) can decline substantially as the
  • study if and how the product ee declines at high conversion. Keywords: enantiomeric excess; enzyme; kinetic mechanisms; kinetic parameters; prochiral; Introduction There is great interest in using enzymatic catalysis in the synthesis of homochiral molecules. An early approach was to use
  • product enantiomers in an unchanging ratio (with one usually strongly favoured). Hence it is usual to quote the enantiomeric excess (ee) of the product as if it were a characteristic property of the enzyme under the given conditions, remaining constant up to high conversions. A search for all publications
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Published 21 Apr 2021
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  • spectra were recorded on a 400 MHz spectrometer, using CDCl3 as solvent. Chemical shift values are reported in ppm with TMS as standard, J values are given in Hertz. Optical rotations were determined by a polarimeter and reported as [α]DT (c in g/100 mL solvent). Enantiomeric excess values were determined
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Published 18 Feb 2021

CF3-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

  • Anthony J. Fernandes,
  • Armen Panossian,
  • Bastien Michelet,
  • Agnès Martin-Mingot,
  • Frédéric R. Leroux and
  • Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

Graphical Abstract
  • amount of the moderately acidic (S)-TRIP (pKa = 3–4 in DMSO [113][114]) in dichloromethane afforded the chiral α-(trifluoromethyl)aminoaryl derivatives 177 in an excellent yield and enantiomeric excess (Scheme 42). The authors proposed that hemiacetal 175 and amine 176 react under the reaction conditions
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Published 03 Feb 2021

The preparation and properties of 1,1-difluorocyclopropane derivatives

  • Kymbat S. Adekenova,
  • Peter B. Wyatt and
  • Sergazy M. Adekenov

Beilstein J. Org. Chem. 2021, 17, 245–272, doi:10.3762/bjoc.17.25

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  • corresponding monoacetate through Alcaligenes sp. lipase-catalyzed hydrolysis with >99% enantiomeric excess. Kirihara et al. have reported the synthesis of the separate enantiomers of 2,2-difluoro-1-aminocyclopropanecarboxylic acid, which are analogs of the naturally occurring 1-aminocyclopropanecarboxylic acid
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Published 26 Jan 2021

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

  • Minzan Zuo,
  • Krishnasamy Velmurugan,
  • Kaiya Wang,
  • Xueqi Tian and
  • Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

Graphical Abstract
  • the modified CDs 7a–9a as sensitizing hosts and (Z)-6 as the guest (Figure 5 and Figure 6) [24]. The compounds 8a, 8b, and 8e could yield a higher enantiomeric excess (10.7% ee in 2 min at 25 °C, host occupancy 91%, 23.9% ee in 25 min at 40 °C, host occupancy 98%, and 8.1% ee in 30 min at 25 °C, host
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Published 18 Jan 2021
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