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Search for "isomerisation" in Full Text gives 81 result(s) in Beilstein Journal of Organic Chemistry.

Ammonium-tagged ruthenium-based catalysts for olefin metathesis in aqueous media under ultrasound and microwave irradiation

  • Łukasz Gułajski,
  • Andrzej Tracz,
  • Katarzyna Urbaniak,
  • Stefan J. Czarnocki,
  • Michał Bieniek and
  • Tomasz K. Olszewski

Beilstein J. Org. Chem. 2019, 15, 160–166, doi:10.3762/bjoc.15.16

Graphical Abstract
  • catalysts (5 mol %) produced the desired product again with quite similar yields under classical conditions. However, the use of microwave or ultrasound irradiation promoted the undesired isomerisation of the C=C bond, thus lowering the yields of the desired product 9 (Table 1, entries 3 and 4). This result
  • is in agreement with the known fact that in protic solvents ruthenium hydrides are formed leading to isomerisation byproducts [66]. Finally, we were pleased to see that the use of ultrasound or microwave irradiation were beneficial for the CM of alcohol 8 with methyl acrylate (10, Table 1, entries 5
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Published 17 Jan 2019

1,8-Bis(dimethylamino)naphthyl-2-ketimines: Inside vs outside protonation

  • A. S. Antonov,
  • A. F. Pozharskii,
  • P. M. Tolstoy,
  • A. Filarowski and
  • O. V. Khoroshilova

Beilstein J. Org. Chem. 2018, 14, 2940–2948, doi:10.3762/bjoc.14.273

Graphical Abstract
  • for IHB formation. The rate and equilibrium constants of this uncatalysed isomerisation [10] depend on the solvent and temperature. By comparing the results obtained in different solvents at equal temperatures, one can see that the Ha Hb exchange rate is noticeably lower in DMSO-d6 (Figures S9–S12 in
  • Supporting Information File 1) than in acetone-d6 and CD3CN (Figures S5–S8 in Supporting Information File 1), while the chemical shift differences between the Ha and Hb signals remain similar in all cases (ca. 1 ppm). The increased energy barrier for the isomerisation could be attributed to the stabilisation
  • . Protonation of DMAN. Protonation equilibria for 2 and 3. Protonation of imine 4a with perchloric acid. Synthesis of investigated substrates (yields obtained by paths a and b are denoted by a corresponding superscript). Preparation of protonated forms of imines 4–7. E/Z-Isomerisation of ketimines 4a–7a
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Published 28 Nov 2018

Unnatural α-amino ethyl esters from diethyl malonate or ethyl β-bromo-α-hydroxyiminocarboxylate

  • Eloi P. Coutant,
  • Vincent Hervin,
  • Glwadys Gagnot,
  • Candice Ford,
  • Racha Baatallah and
  • Yves L. Janin

Beilstein J. Org. Chem. 2018, 14, 2853–2860, doi:10.3762/bjoc.14.264

Graphical Abstract
  • out that a chromatography was enough to achieve its isomerisation into 2af. Interestingly, we also found out that the excess 2-methylfuran (48af) was not required and that the reaction proceeded much faster and led directly to the α-hydroxyimino ester 2af if tetrabutylammonium bromide was added as a
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Published 16 Nov 2018

Synthesis and biological evaluation of 1,2-disubstituted 4-quinolone analogues of Pseudonocardia sp. natural products

  • Stephen M. Geddis,
  • Teodora Coroama,
  • Suzanne Forrest,
  • James T. Hodgkinson,
  • Martin Welch and
  • David R. Spring

Beilstein J. Org. Chem. 2018, 14, 2680–2688, doi:10.3762/bjoc.14.245

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  • allyl-substituted substrates 13ab and 13bb underwent an isomerisation under the reaction conditions, with the double bond moving into conjugation with the amine to give inseparable mixtures of enamine-type products 14ab and 14bb. Given the likely hydrolytic instability of synthetic precursors possessing
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Published 19 Oct 2018

Heterogeneous acidic catalysts for the tetrahydropyranylation of alcohols and phenols in green ethereal solvents

  • Ugo Azzena,
  • Massimo Carraro,
  • Gloria Modugno,
  • Luisa Pisano and
  • Luigi Urtis

Beilstein J. Org. Chem. 2018, 14, 1655–1659, doi:10.3762/bjoc.14.141

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  • isomerisation of the acid-sensitive allylic alcohol 1j [34]. To stress the usefulness of a tetrahydropyranylation reaction performed in a green ethereal solvent and in the presence of a heterogeneous acidic catalyst, we realized two one-pot procedures employing either 2-MeTHF or CPME as a solvent. Accordingly
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Published 03 Jul 2018

Atom-economical group-transfer reactions with hypervalent iodine compounds

  • Andreas Boelke,
  • Peter Finkbeiner and
  • Boris J. Nachtsheim

Beilstein J. Org. Chem. 2018, 14, 1263–1280, doi:10.3762/bjoc.14.108

Graphical Abstract
  • copper species D to provide complex F. Isomerisation to the cis-palladium complex G and subsequent reductive elimination finally delivers 30. In such sequences, the iodane can also be prone to autooxidation processes, as demonstrated by Dauban and co-workers. Alkyl-substituted PIDA derivatives 20c are
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Published 30 May 2018

One hundred years of benzotropone chemistry

  • Arif Dastan,
  • Haydar Kilic and
  • Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

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  • there are limited reports on the o-quinoidal 3,4-benzotropones 13. Considering the known reactivity of benzocyclobutenes, i.e., their isomerisation to o-quinodimethanes, Tsuji’s group used 6,7-benzobicyclo[3.2.0]hepta-3,6-dien-2-one (230) as a precursor to produce 13. They reported the first generation
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Published 23 May 2018

Volatiles from three genome sequenced fungi from the genus Aspergillus

  • Jeroen S. Dickschat,
  • Ersin Celik and
  • Nelson L. Brock

Beilstein J. Org. Chem. 2018, 14, 900–910, doi:10.3762/bjoc.14.77

Graphical Abstract
  • ), isodaucene (18), and trans-dauca-8,11-diene (20). The biosynthesis of these compounds requires isomerisation of FPP to NPP, followed by cyclisation to K that results in 17 and 18 by deprotonation (Scheme 3). A 1,2-hydride shift to L and loss of a proton explains the main product 19. For compound 20 a
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Published 24 Apr 2018

Aminosugar-based immunomodulator lipid A: synthetic approaches

  • Alla Zamyatina

Beilstein J. Org. Chem. 2018, 14, 25–53, doi:10.3762/bjoc.14.3

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Published 04 Jan 2018

The synthesis of the 2,3-difluorobutan-1,4-diol diastereomers

  • Robert Szpera,
  • Nadia Kovalenko,
  • Kalaiselvi Natarajan,
  • Nina Paillard and
  • Bruno Linclau

Beilstein J. Org. Chem. 2017, 13, 2883–2887, doi:10.3762/bjoc.13.280

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  • isomerisation (see Supporting Information File 1). Epoxide opening with the recently described TBAF/KHF2 [22] was also possible, but in lower yield (75%, not shown). Incidentally, it was also found that the subsequent deoxofluorination reaction was somewhat higher yielding when DAST was added at rt over just 5
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Published 27 Dec 2017
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  • 1 and 2 were obtained by epimerization at C9. Mixtures of the isomers of 1 were formed in TBAF desilylation of Cinchona 4-TMS-triazole derivatives. Partial isomerisation of 2a into 2b was performed by transient deprotonation using in situ generated sodium methylsulfinylmethylide (Scheme 1). Both
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Published 22 Nov 2017

Synthesis and metal binding properties of N-alkylcarboxyspiropyrans

  • Alexis Perry and
  • Christina J. Kousseff

Beilstein J. Org. Chem. 2017, 13, 1542–1550, doi:10.3762/bjoc.13.154

Graphical Abstract
  • ., C4SP, Scheme 1) which exist in photo-controlled equilibrium with their zwitterionic, fully-conjugated merocyanine isomer [1] (e.g., C4MC, Scheme 1). The controllable nature of this isomerisation and the dramatic differences in physical and chemical properties displayed by the isomeric forms, coupled
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Published 04 Aug 2017

Synthesis of alkynyl-substituted camphor derivatives and their use in the preparation of paclitaxel-related compounds

  • M. Fernanda N. N. Carvalho,
  • Rudolf Herrmann and
  • Gabriele Wagner

Beilstein J. Org. Chem. 2017, 13, 1230–1238, doi:10.3762/bjoc.13.122

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  • the C–C bond between the atoms bearing the OH and NH groups (ring enlargement). The result is an isomerisation of 4a and 4b to form tricyclic compounds 7 containing a nine-membered carbocyclic ring (Scheme 3a) [27]. Isomerisations are the best examples for a perfect “atom economy” [28][29][30] since
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Published 26 Jun 2017

Fluorescent carbon dots from mono- and polysaccharides: synthesis, properties and applications

  • Stephen Hill and
  • M. Carmen Galan

Beilstein J. Org. Chem. 2017, 13, 675–693, doi:10.3762/bjoc.13.67

Graphical Abstract
  • as the major component in the preparation of this type of CD, as evidenced by 1H, 13C NMR, FTIR and MALDI–MS (Scheme 19). The authors proposed that initial acid catalysed degradation of the sucrose disaccharide to its monosaccharide constituents fructose and glucose, followed by glucose isomerisation
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Published 10 Apr 2017

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

Graphical Abstract
  • GPP to 1 is prevented by the topological constraints associated with the (2E) geometry which necessitates the isomerisation of GPP (4) to linalyl diphosphate (LPP, 5) followed by an anti,endo-SN’-cyclisation [14], but the stereochemical course of this reaction is not readily clear and may proceed via
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Published 04 Nov 2016

Biocatalysis for the application of CO2 as a chemical feedstock

  • Apostolos Alissandratos and
  • Christopher J. Easton

Beilstein J. Org. Chem. 2015, 11, 2370–2387, doi:10.3762/bjoc.11.259

Graphical Abstract
  • formed through isomerisation and recycled into two equivalents of acetyl-CoA (10). This route is encountered in two separate pathways, namely the 3-hydroxypropionate/4-hydroxybutyrate cycle and the 3-hydroxypropionate bicycle. An alternative CO2 fixation route is found in the dicarboxylate/4
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Published 01 Dec 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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  • absence of TiO2 showed that E/Z isomerisation was significant (25, 52–79%). Rather complex product mixtures containing E and Z-isomers of unreacted alkene, as well as low yields of dihydrobenzofurans 26, were obtained from 24a–c. Poor results were obtained from acids with aromatic and oxime acceptor
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Published 09 Sep 2015
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  • lead to assume either instability of trans-(4-RC6F4)PdL2Ar towards isomerisation to cis-isomer or the direct formation of reactive complex cis-(4-RC6F4)PdL2Ar during the transmetallation with closely related borates K[4-RC6F4BF3] (Scheme 8). At the next step, cis-(4-RC6F4)PdL2Ar undergoes reductive
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Published 04 May 2015

The reactions of 2-ethoxymethylidene-3-oxo esters and their analogues with 5-aminotetrazole as a way to novel azaheterocycles

  • Marina V. Goryaeva,
  • Yanina V. Burgart,
  • Marina A. Ezhikova,
  • Mikhail I. Kodess and
  • Viktor I. Saloutin

Beilstein J. Org. Chem. 2015, 11, 385–391, doi:10.3762/bjoc.11.44

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  • explained by the properties of 5-AT. Thus, due to the tendency of the tetrazole ring towards isomerisation to an azide group, 3-oxo esters 1a–c with alkyl substituents form 2-azidopyrimidines 2a–c that are capable for further modification at the electrophilic centre C-6 and the azide group. Another
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Published 23 Mar 2015

Synthesis of the furo[2,3-b]chromene ring system of hyperaspindols A and B

  • Danielle L. Paterson and
  • David Barker

Beilstein J. Org. Chem. 2015, 11, 265–270, doi:10.3762/bjoc.11.29

Graphical Abstract
  • protons (Figure 5) [26]. Overall this represents an anti-relationship between H-8 and H-10 confirming 7b to be the C-10 epimer of 7a. The ratio of diastereoisomers in ketal 22 was 1:1, however in the cyclised products 7 the ratio of diastereoisomers 7a to 7b was 1.6:1. This suggests partial isomerisation
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Published 17 Feb 2015

Electrochemical selenium- and iodonium-initiated cyclisation of hydroxy-functionalised 1,4-dienes

  • Philipp Röse,
  • Steffen Emge,
  • Jun-ichi Yoshida and
  • Gerhard Hilt

Beilstein J. Org. Chem. 2015, 11, 174–183, doi:10.3762/bjoc.11.18

Graphical Abstract
  • the straightforward synthesis of various 1,4-dienols of type 2 and the mild reaction conditions made it possible to generate and isolate the products without isomerisation of the double bonds towards undesired side-products. Transformation of 1,4-dienols via electro-generated selenium cations The 1,4
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Published 28 Jan 2015

Synthesis and bioactivity of analogues of the marine antibiotic tropodithietic acid

  • Patrick Rabe,
  • Tim A. Klapschinski,
  • Nelson L. Brock,
  • Christian A. Citron,
  • Paul D’Alvise,
  • Lone Gram and
  • Jeroen S. Dickschat

Beilstein J. Org. Chem. 2014, 10, 1796–1801, doi:10.3762/bjoc.10.188

Graphical Abstract
  • product was sufficiently pure for its direct usage in a Diels–Alder reaction with tetrachlorocyclopropene, resulting in the adduct 19 as a single stereoisomer. The formation of only one stereoisomer is explainable by an E/Z isomerisation of 18 and a Diels–Alder reaction that only proceeds from (Z)-18, but
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Published 06 Aug 2014

Selective allylic hydroxylation of acyclic terpenoids by CYP154E1 from Thermobifida fusca YX

  • Anna M. Bogazkaya,
  • Clemens J. von Bühler,
  • Sebastian Kriening,
  • Alexandrine Busch,
  • Alexander Seifert,
  • Jürgen Pleiss,
  • Sabine Laschat and
  • Vlada B. Urlacher

Beilstein J. Org. Chem. 2014, 10, 1347–1353, doi:10.3762/bjoc.10.137

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  • oxidation, reduction, isomerisation or conjugation reactions [14]. Furthermore, in some bacteria assimilating terpenes as carbon sources, the first oxidation step is a P450-mediated allylic hydroxylation or allylic rearrangement reaction [15]. In vitro investigations demonstrated that P450 enzymes can
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Published 13 Jun 2014

Dimerisation, rhodium complex formation and rearrangements of N-heterocyclic carbenes of indazoles

  • Zong Guan,
  • Jan C. Namyslo,
  • Martin H. H. Drafz,
  • Martin Nieger and
  • Andreas Schmidt

Beilstein J. Org. Chem. 2014, 10, 832–840, doi:10.3762/bjoc.10.79

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  • frequencies on Z→E isomerisation. The following scheme presents diagnostic peak assignments of the 1H and 13C NMR spectra, taken at 400 and 100 MHz in CDCl3, respectively. According to DFT calculations the conversion of 13a to 14a requires an activation energy of ΔG# = +79 kJ/mol (ΔE = +89 kJ/mol) while the
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Published 10 Apr 2014

Synthesis of complex intermediates for the study of a dehydratase from borrelidin biosynthesis

  • Frank Hahn,
  • Nadine Kandziora,
  • Steffen Friedrich and
  • Peter F. Leadlay

Beilstein J. Org. Chem. 2014, 10, 634–640, doi:10.3762/bjoc.10.55

Graphical Abstract
  • , which might be able to catalyze the inversion of a double bond configuration. Consequently, the Z-configured double bond must be installed either directly by BorDH3 or by E/Z-isomerisation of an initially formed E-configured double bond via a not yet elucidated mechanism in downstream biosynthetic
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Published 11 Mar 2014
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