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Search for "stereoisomers" in Full Text gives 229 result(s) in Beilstein Journal of Organic Chemistry. Showing first 200.

Combined experimental and theoretical studies of regio- and stereoselectivity in reactions of β-isoxazolyl- and β-imidazolyl enamines with nitrile oxides

  • Ilya V. Efimov,
  • Marsel Z. Shafikov,
  • Nikolai A. Beliaev,
  • Natalia N. Volkova,
  • Tetyana V. Beryozkina,
  • Wim Dehaen,
  • Zhijin Fan,
  • Viktoria V. Grishko,
  • Gert Lubec,
  • Pavel A. Slepukhin and
  • Vasiliy A. Bakulev

Beilstein J. Org. Chem. 2016, 12, 2390–2401, doi:10.3762/bjoc.12.233

Graphical Abstract
  • . The isoxazolines transform to aromatic isoxazoles 4 during purification. Fortunately, we were able to isolate the products of the reaction of β-imidazolyl enamines 1a,b with hydroxamoyl chlorides 2a,d,g, and the novel imidazolylisoxazolines 3a–c as pure stereoisomers in 67, 65 and 21% yields
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Published 15 Nov 2016

β-Amino functionalization of cinnamic Weinreb amides in ionic liquid

  • Yi-Ning Wang,
  • Guo-Xiang Sun and
  • Gang Qi

Beilstein J. Org. Chem. 2016, 12, 2372–2377, doi:10.3762/bjoc.12.231

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  • interesting phenomenon can be seen; namely, the difference of the proton chemical shifts of the hydrogen atoms of the nitrobenzenesulfonylamines. Compared with the chemical shifts of these protons belonging to the syn-stereoisomers, the signals of the same kind of protons of the anti-stereoisomers move to
  • addition, because of the resonance structures (Scheme 4), the hydrogen bonding can be further strengthened by the oxygen which is more electronegative. As a result, the chemical shifts of these protons belonging to the anti-stereoisomers can move to much lower fields than those of the similar hydrogen
  • atoms of not only the syn-stereoisomers but also the β-amino compounds derived from α,β-unsaturated ketones. This hypothesis can be supported by an unexpected transformation. When aziridine 7-B was purified by flash column chromatography, part of the aziridine ring was opened by a chlorine anion to form
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Published 11 Nov 2016

Useful access to enantiomerically pure protected inositols from carbohydrates: the aldohexos-5-uloses route

  • Felicia D’Andrea,
  • Giorgio Catelani,
  • Lorenzo Guazzelli and
  • Venerando Pistarà

Beilstein J. Org. Chem. 2016, 12, 2343–2350, doi:10.3762/bjoc.12.227

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  • level is required. For this reason, many research efforts were directed toward the investigation of the structure–activity relationship (SAR) between inositol phosphates and biomacromolecules. These studies require various regio- and stereoisomers of inositol phosphates [6][7] and have prompted the
  • material but differs from previous work in that it is metal-free. The first application of this approach was described by Kiely [31][32] who obtained a sample of myo-inositol in a mixture with other non characterised stereoisomers by treating D-xylo-hexos-5-ulose [31] and its 6-phosphate [32] with 0.1 N
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Published 08 Nov 2016

A detailed view on 1,8-cineol biosynthesis by Streptomyces clavuligerus

  • Jan Rinkel,
  • Patrick Rabe,
  • Laura zur Horst and
  • Jeroen S. Dickschat

Beilstein J. Org. Chem. 2016, 12, 2317–2324, doi:10.3762/bjoc.12.225

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  • representing various stereoisomers and constitutional isomers with different positioning of olefinic double bonds or alcohol functions are known just for sesquiterpenes [11]. The structural diversity of terpenoids can be further increased by the action of tailoring enzymes such as cytochrome P450
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Published 04 Nov 2016

A new and expeditious synthesis of all enantiomerically pure stereoisomers of rosaprostol, an antiulcer drug

  • Wiesława Perlikowska,
  • Remigiusz Żurawiński and
  • Marian Mikołajczyk

Beilstein J. Org. Chem. 2016, 12, 2234–2239, doi:10.3762/bjoc.12.215

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  • Wieslawa Perlikowska Remigiusz Zurawinski Marian Mikolajczyk Department of Heteroorganic Chemistry, Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Łódź, Poland 10.3762/bjoc.12.215 Abstract Four enantiomerically pure stereoisomers of
  • to 64%. The remaining two stereoisomers, (−)-1b and (+)-1d, were obtained from (−)-1a and (+)-1c in 71 and 68% yield, respectively, by a two-reaction sequence, in which a Mitsunobu inversion of configuration at C-5 was the key step. Keywords: antiulcer drug; chiral resolution; rosaprostol
  • stereostructure–bioactivity relationship in biologically active compounds [18][19], including selected prostanoids [20][21][22], we decided to synthesize all four rosaprostol stereoisomers 1a–d in enantiomerically pure form (Figure 2). The two rosaprostol stereoisomers 1c and 1d have an absolute configuration at
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Published 21 Oct 2016

Diels–Alder reactions in confined spaces: the influence of catalyst structure and the nature of active sites for the retro-Diels–Alder reaction

  • Ángel Cantín,
  • M. Victoria Gomez and
  • Antonio de la Hoz

Beilstein J. Org. Chem. 2016, 12, 2181–2188, doi:10.3762/bjoc.12.208

Graphical Abstract
  • ] in where different stereoisomers could be obtained. Lewis-acid centers contained within the framework of zeolite beta (Zr-β, Sn-β) are useful catalysts in the Diels–Alder reaction for the production of bio-based terephthalic acid precursors, one of the monomers for the synthesis of polyethylene
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Published 13 Oct 2016

Biosynthesis of oxygen and nitrogen-containing heterocycles in polyketides

  • Franziska Hemmerling and
  • Frank Hahn

Beilstein J. Org. Chem. 2016, 12, 1512–1550, doi:10.3762/bjoc.12.148

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Published 20 Jul 2016

Conjugate addition–enantioselective protonation reactions

  • James P. Phelan and
  • Jonathan A. Ellman

Beilstein J. Org. Chem. 2016, 12, 1203–1228, doi:10.3762/bjoc.12.116

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  • stabilize the carbanion intermediate, also increases the stereocenter’s susceptibility to racemization under the reaction conditions. Moreover, enolate intermediates can adopt E- or Z-geometries that, upon protonation, generally lead to opposite stereoisomers. Because enantioselective protonation is a
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Published 15 Jun 2016

Modular synthesis of the pyrimidine core of the manzacidins by divergent Tsuji–Trost coupling

  • Sebastian Bretzke,
  • Stephan Scheeff,
  • Felicitas Vollmeyer,
  • Friederike Eberhagen,
  • Frank Rominger and
  • Dirk Menche

Beilstein J. Org. Chem. 2016, 12, 1111–1121, doi:10.3762/bjoc.12.107

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  • addition in more general terms and analyzed the addition reactions of allylmagnesium bromide both to 29 and 30. Notably, this route would allow to access all possible stereoisomers of the manzacidins, in agreement with the stereochemical diversity of this class of natural products. In detail, the synthesis
  • urea-type cyclization precursor 19. Stereodivergent synthesis of 1,3-syn- and anti-tetrahydropyrimidinones [31]. Stereoselective synthesis of all possible stereoisomers of the manzacidin core amine by asymmetric addition to chiral tert-butanesulfinyl ketimines. Synthesis of the authentic cyclization
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Published 02 Jun 2016

Efficient syntheses of climate relevant isoprene nitrates and (1R,5S)-(−)-myrtenol nitrate

  • Sean P. Bew,
  • Glyn D. Hiatt-Gipson,
  • Graham P. Mills and
  • Claire E. Reeves

Beilstein J. Org. Chem. 2016, 12, 1081–1095, doi:10.3762/bjoc.12.103

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  • ]. Evidently, to comprehensively investigate the role of individual IPNs within climate chemistry it is important that any synthetic protocol employed to generate IPNs affords either individual C=C stereoisomers or generates readily separable stereoisomers of the IPNs. Thus although the lack of synthetic
  • purification afforded stereoisomers (E)-58 and (Z)-59 in a 2:1 ratio, respectively, and combined, unoptimized, 71% yield. Separation of the stereoisomers via flash column chromatography was straightforward. Pure (E)-58 and (Z)-59 were afforded with physicochemical properties essentially identical to those
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Published 27 May 2016

Marine-derived myxobacteria of the suborder Nannocystineae: An underexplored source of structurally intriguing and biologically active metabolites

  • Antonio Dávila-Céspedes,
  • Peter Hufendiek,
  • Max Crüsemann,
  • Till F. Schäberle and
  • Gabriele M. König

Beilstein J. Org. Chem. 2016, 12, 969–984, doi:10.3762/bjoc.12.96

Graphical Abstract
  • haliangicin stereoisomers, which differed in the configuration of the three terminal double bonds in the tetraene moiety. Each of the isomers haliangicin, haliangicin B, haliangicin C and haliangicin D happened to be present with two different configurations around the epoxy group. The NOESY spectra showed
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Published 13 May 2016

Recent advances in N-heterocyclic carbene (NHC)-catalysed benzoin reactions

  • Rajeev S. Menon,
  • Akkattu T. Biju and
  • Vijay Nair

Beilstein J. Org. Chem. 2016, 12, 444–461, doi:10.3762/bjoc.12.47

Graphical Abstract
  • - and galacto-configured dialdehydes 66 were promoted by the triazolium carbene precatalyst 22 to produce single inosose stereoisomers 67 in high yields (Scheme 40) [57]. Stereospecific reduction and deprotection of the inosose derivatives furnished allo- and epi-inositol in good yields. The camphor
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Published 09 Mar 2016

Aluminacyclopentanes in the synthesis of 3-substituted phospholanes and α,ω-bisphospholanes

  • Vladimir A. D’yakonov,
  • Alevtina L. Makhamatkhanova,
  • Rina A. Agliullina,
  • Leisan K. Dilmukhametova,
  • Tat’yana V. Tyumkina and
  • Usein M. Dzhemilev

Beilstein J. Org. Chem. 2016, 12, 406–412, doi:10.3762/bjoc.12.43

Graphical Abstract
  • BuPCl2, the reaction with 3-benzyl-1-ethylaluminacyclopentane 1f affords the corresponding phospholanes 2g,h with one of the isomers predominating (Table 1). In the case of 3-cyclohexyl- and 3-(сyclohex-3-en-1-yl)-1-phenylphospholanes (2d and 2e), the number of stereoisomers increases owing to the
  • /methanol = 5:3:1) and characterized in a separate fraction (Scheme 4). It should be noted that the phosphorus signals of major intensity of 2-aryl phospholane oxides 8a, 8b, 8d, 8e, 8f, corresponding to one of the stereoisomers, are shifted upfield by ca. 5–7 ppm with respect to those of 3-aryl-substituted
  • the proximate asymmetric centres at C-3 and С-3′. Ratios of stereoisomers were determined by HPLC method as 2:1 (see Supporting Information File 2, Figure S1). Organophosphorus compounds, including cyclic ones, are known to readily form complexes with transition metals, which are extensively studied
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Published 02 Mar 2016

Diastereoselective synthesis of new O-alkylated and C-branched inositols and their corresponding fluoro analogues

  • Charlotte Collet,
  • Françoise Chrétien,
  • Yves Chapleur and
  • Sandrine Lamandé-Langle

Beilstein J. Org. Chem. 2016, 12, 353–361, doi:10.3762/bjoc.12.39

Graphical Abstract
  • ; Introduction Inositol is a trivial name used to describe cyclohexanehexol compounds. Nine stereoisomers exist differing in the relative orientation of the hydroxy groups, the most naturally abounding and biologically important is myo-inositol [1][2]. The chemistry of inositols has been the theme of several
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Published 25 Feb 2016

Interactions of cyclodextrins and their derivatives with toxic organophosphorus compounds

  • Sophie Letort,
  • Sébastien Balieu,
  • William Erb,
  • Géraldine Gouhier and
  • François Estour

Beilstein J. Org. Chem. 2016, 12, 204–228, doi:10.3762/bjoc.12.23

Graphical Abstract
  • organophosphates is to be considered important insofar as the individual stereoisomers of a neurotoxic agent do not share the same level of toxicity [20]. Sarin (compounds 14a and 14b, Figure 5), cyclosarin (compounds 15a and 15b, Figure 5) and tabun (compounds 16a and 16b, Figure 5) consist of a mixture of two
  • enantiomers. Due to the presence of two chiral centers (the phosphorus atom and the carbon atom of the 1,2,2-trimethylpropyloxy group), soman presents four stereoisomers: C(S)P(S), C(R)P(S), C(S)P(R) and C(R)P(R) (compounds 17a–d, Figure 5). CDs can tune a reaction mechanism in two ways: (a) by creating a
  • agent stereoisomers’ absolute configuration of the phosphorus atom was not firmly established. Thus, the van Hooidonk and Breebaart’s work dating from 1970, it is highly probable that they did not attributed the correct absolute configurations to the enantiomers of sarin, which means that the (S
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Published 05 Feb 2016

Hydroquinone–pyrrole dyads with varied linkers

  • Hao Huang,
  • Christoffer Karlsson,
  • Maria Strømme,
  • Martin Sjödin and
  • Adolf Gogoll

Beilstein J. Org. Chem. 2016, 12, 89–96, doi:10.3762/bjoc.12.10

Graphical Abstract
  • % yield after 3 h. When the reaction was performed at room temperature, only 20% yield was obtained after 48 h. Close to equal quantities of cis-4c and trans-4c were formed in this reaction, and were separated chromatographically. Having access to both isomers was desirable, since the stereoisomers are
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Published 18 Jan 2016

Organocatalytic and enantioselective Michael reaction between α-nitroesters and nitroalkenes. Syn/anti-selectivity control using catalysts with the same absolute backbone chirality

  • Jose I. Martínez,
  • Uxue Uria,
  • Maria Muñiz,
  • Efraím Reyes,
  • Luisa Carrillo and
  • Jose L. Vicario

Beilstein J. Org. Chem. 2015, 11, 2577–2583, doi:10.3762/bjoc.11.277

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  • despite the advances made in the field, an important challenge arises when a molecule containing multiple stereocentres has to be prepared because the access to all possible stereoisomers is not usually straightforward. While obtaining one or other mirror image of the target molecule can also be easily
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Published 14 Dec 2015

[2.2]Paracyclophane derivatives containing tetrathiafulvalene moieties

  • Laura G. Sarbu,
  • Lucian G. Bahrin,
  • Peter G. Jones,
  • Lucian M. Birsa and
  • Henning Hopf

Beilstein J. Org. Chem. 2015, 11, 1917–1921, doi:10.3762/bjoc.11.207

Graphical Abstract
  • -dithiolium salts; [2.2]paracyclophane; regioselective bromination; stereoisomers; tetrathiafulvalenes; Introduction Tetrathiafulvalene (TTF) and its derivatives have been extensively studied with respect to their applications as organic metals and superconductors [1][2]. These properties are a consequence
  • a mixture of inseparable isomeric tetrathiafulvalenes 7 in 17% yield. Since compound 6 already exhibits planar chirality (racemate Rp/Sp), the theoretical number of stereoisomers of the tetrathiafulvalene 7 should be six as follows: cis-(Sp,Sp) with cis-(Rp,Rp) and trans-(Sp,Sp) with trans-(Rp,Rp
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Published 15 Oct 2015

Cross metathesis of unsaturated epoxides for the synthesis of polyfunctional building blocks

  • Meriem K. Abderrezak,
  • Kristýna Šichová,
  • Nancy Dominguez-Boblett,
  • Antoine Dupé,
  • Zahia Kabouche,
  • Christian Bruneau and
  • Cédric Fischmeister

Beilstein J. Org. Chem. 2015, 11, 1876–1880, doi:10.3762/bjoc.11.201

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  • performances (Table 1, entries 7 and 8). Similarly, the cross metathesis of 1 with acrylonitrile was conducted to furnish the bifunctional derivative 3 in 71% yield as a mixture of stereoisomers. In that case, high conversions and yields could only be obtained by means of slow addition of the catalyst and high
  • dilution (Scheme 2) [13]. As we already observed, [13][14][22] together with other groups, [35][36] in various cross metathesis reactions involving acrylonitrile, the cross metathesis product 3 was obtained as a mixture of E (minor) and Z (major) stereoisomers. With these two compounds in hands, we turned
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Published 08 Oct 2015

Mechanism, kinetics and selectivity of selenocyclization of 5-alkenylhydantoins: an experimental and computational study

  • Biljana M. Šmit,
  • Radoslav Z. Pavlović,
  • Dejan A. Milenković and
  • Zoran S. Marković

Beilstein J. Org. Chem. 2015, 11, 1865–1875, doi:10.3762/bjoc.11.200

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  • addition of PhSeCl to the double bond, is presented in Scheme 1, while the 5-exo pathway with all stereoisomers is presented in Scheme 2. The first step of the proposed mechanism producing the seleniranium cation, followed by anti-attack of the external nucleophile (Cl−) to the double bond [35] of 5
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Published 07 Oct 2015

Preparative semiconductor photoredox catalysis: An emerging theme in organic synthesis

  • David W. Manley and
  • John C. Walton

Beilstein J. Org. Chem. 2015, 11, 1570–1582, doi:10.3762/bjoc.11.173

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  • yield of 75%. Phenyl- and 2-thienylacetic acids afforded adducts accompanied by the dimers bibenzyl (18%) and 1,2-di(thiophen-2-yl)ethane (27%), respectively. Significantly, Boc-protected α-amino acids also proved amenable and yielded adducts as 1:1 mixtures of stereoisomers. Chirality was not preserved
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Published 09 Sep 2015

Cathodic hydrodimerization of nitroolefins

  • Michael Weßling and
  • Hans J. Schäfer

Beilstein J. Org. Chem. 2015, 11, 1163–1174, doi:10.3762/bjoc.11.131

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  • the Marple electrode and converted to SCE. Hydrodimerization of nitroalkene 14 and 15. (a) Intramolecular hydrocoupling of dinitrodiene 16 and (b) hydrodimerization of 1-nitrocyclohexene (17). Possible stereoisomers and their mirror images for the hydrodimers 2 and 18–23; R and S are the
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Published 14 Jul 2015

Advances in the synthesis of functionalised pyrrolotetrathiafulvalenes

  • Luke J. O’Driscoll,
  • Sissel S. Andersen,
  • Marta V. Solano,
  • Dan Bendixen,
  • Morten Jensen,
  • Troels Duedal,
  • Jess Lycoops,
  • Cornelia van der Pol,
  • Rebecca E. Sørensen,
  • Karina R. Larsen,
  • Kenneth Myntman,
  • Christian Henriksen,
  • Stinne W. Hansen and
  • Jan O. Jeppesen

Beilstein J. Org. Chem. 2015, 11, 1112–1122, doi:10.3762/bjoc.11.125

Graphical Abstract
  • complication encountered with such functionalised TTFs is the existence of cis and trans stereoisomers. The investigation of the properties of a single isomer is challenging, not only due to difficulties in the separation of the isomers, but also because it is possible for the isomers to interconvert in the
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Published 03 Jul 2015

Synthesis of novel N-cyclopentenyl-lactams using the Aubé reaction

  • Madhuri V. Shinde,
  • Rohini S. Ople,
  • Ekta Sangtani,
  • Rajesh Gonnade and
  • D. Srinivasa Reddy

Beilstein J. Org. Chem. 2015, 11, 1060–1067, doi:10.3762/bjoc.11.119

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  • Carell et al. in 2007 [40]. The work of Aubé on AAC (azide–alkyne cycloaddition) chemistry also gives a good indication that equilibrating allylic azide stereoisomers can selectively participate in reactions [37][38][39][40][41][42][43][44][45]. In 2000, Aubé et al. proposed a mechanism for the
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Published 23 Jun 2015

Discrete multiporphyrin pseudorotaxane assemblies from di- and tetravalent porphyrin building blocks

  • Mirko Lohse,
  • Larissa K. S. von Krbek,
  • Sebastian Radunz,
  • Suresh Moorthy,
  • Christoph A. Schalley and
  • Stefan Hecht

Beilstein J. Org. Chem. 2015, 11, 748–762, doi:10.3762/bjoc.11.85

Graphical Abstract
  • ethers on its corresponding axle are possible. One can therefore expect a mixture of stereoisomers to form. In the simplest case, A2@C2, two enantiomers and one meso-form are expected to exist, which should result in two overlapping sets of signals. For the other three complexes, the situation is even
  • . The formation of unspecific complexes as well as fragmentation upon ionization have been found to be quite limited so that the picture obtained from the mass spectra can be expected to provide realistic insights into the composition of the complexes present in solution. As all stereoisomers have the
  • broaden significantly, which is in agreement with the assumption that upon complexation the number of signals increases because the methylene protons become diasterotopic and different supramolecular stereoisomers can form. However, based on the present NMR spectroscopy data (Figure 7 and Figure 8) one
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Published 12 May 2015
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