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Search for "oxonium" in Full Text gives 55 result(s) in Beilstein Journal of Organic Chemistry.

Photocatalyzed synthesis of isochromanones and isobenzofuranones under batch and flow conditions

  • Manuel Anselmo,
  • Lisa Moni,
  • Hossny Ismail,
  • Davide Comoretto,
  • Renata Riva and
  • Andrea Basso

Beilstein J. Org. Chem. 2017, 13, 1456–1462, doi:10.3762/bjoc.13.143

Graphical Abstract
  • oxonium ion 7 evolves to isochromanone 4c, while the 4-methoxybenzyl carbocation is sufficiently long lived to react with acetonitrile and afford acetamide 5 upon reaction with traces of water. Interestingly enough, when the reaction was performed in acetone, compound 4c was isolated in lower yield (60
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Published 25 Jul 2017

Unusual reactions of diazocarbonyl compounds with α,β-unsaturated δ-amino esters: Rh(II)-catalyzed Wolff rearrangement and oxidative cleavage of N–H-insertion products

  • Valerij A. Nikolaev,
  • Jury J. Medvedev,
  • Olesia S. Galkina,
  • Ksenia V. Azarova and
  • Christoph Schneider

Beilstein J. Org. Chem. 2016, 12, 1904–1910, doi:10.3762/bjoc.12.180

Graphical Abstract
  • intermediates generated from diazo compounds (ammonium, oxonium, C=X-ylides and others) to react with a variety of electrophiles/nucleophiles yielding complex and challenging organic molecules from relatively straightforward initial compounds [9][10]. The research group by Hu and co-workers elaborated recently
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Published 25 Aug 2016

Three-component synthesis of highly functionalized aziridines containing a peptide side chain and their one-step transformation into β-functionalized α-ketoamides

  • Lena Huck,
  • Juan F. González,
  • Elena de la Cuesta and
  • J. Carlos Menéndez

Beilstein J. Org. Chem. 2016, 12, 1772–1777, doi:10.3762/bjoc.12.166

Graphical Abstract
  • ether function existent in aziridine derivatives 2 because of the presence of the 2-methoxy substituent would furnish oxonium species 7 via a Neber reaction. Its O-demethylation by the trifluoroacetate anion would yield compound 8, whose amino group would finally be trifluoroacetylated by the methyl
  • trifluoroacetate liberated in the previous step, to give 6. Alternatively, loss of a molecule of methanol from starting compound 2 would lead to intermediate 5 (see Scheme 3), whose reaction with trifluoroacetic acid would furnish 9. Neber-type chemistry would afford the oxonium species 10, which would finally be
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Published 08 Aug 2016

The hydrolysis of geminal ethers: a kinetic appraisal of orthoesters and ketals

  • Sonia L. Repetto,
  • James F. Costello,
  • Craig P. Butts,
  • Joseph K. W. Lam and
  • Norman M. Ratcliffe

Beilstein J. Org. Chem. 2016, 12, 1467–1475, doi:10.3762/bjoc.12.143

Graphical Abstract
  • geometry elements to optimise. In all cases, the five-membered ring moved towards the final planar oxonium ion, but no enthalpic barrier was found for the C(2)–OMe bond cleavage. This supports entropic control of this elimination reaction, and it is therefore not surprising that the more planar ring for
  • to elimination of the OMe group and formation of the intermediate oxonium ion. The dual performance of cyclic geminal ethers as FDII for jet fuels will be reported shortly. Experimental All preparative operations were performed at the synthetic laboratories of the School of Chemistry, University of
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Published 15 Jul 2016

The chemical behavior of terminally tert-butylated polyolefins

  • Dagmar Klein,
  • Henning Hopf,
  • Peter G. Jones,
  • Ina Dix and
  • Ralf Hänel

Beilstein J. Org. Chem. 2015, 11, 1246–1258, doi:10.3762/bjoc.11.139

Graphical Abstract
  • group is readily seen in the IR spectrum (νmax = 1702 cm−1) and the carbonyl carbon signal in the 13C NMR spectrum at δ = 217 ppm is also of particular diagnostic value. We propose that 31 is produced from epoxide 29 by initial protonation to the oxonium ion 30, which then undergoes a Wagner–Meerwein
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Published 24 Jul 2015

Novel carbocationic rearrangements of 1-styrylpropargyl alcohols

  • Christine Basmadjian,
  • Fan Zhang and
  • Laurent Désaubry

Beilstein J. Org. Chem. 2015, 11, 1017–1022, doi:10.3762/bjoc.11.114

Graphical Abstract
  • intermediate 12 that undergoes an oxo-cyclization to afford an oxonium en route to furan 13 (pathway B). Alternatively, intermediate 12 may result from the allylic [1,3]-transposition of a perrhenate ester [10]. Replacement of the highly electron-donating 2,4,6-trimethoxyphenyl group by a 4-chlorophenyl
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Published 15 Jun 2015

C-5’-Triazolyl-2’-oxa-3’-aza-4’a-carbanucleosides: Synthesis and biological evaluation

  • Roberto Romeo,
  • Caterina Carnovale,
  • Salvatore V. Giofrè,
  • Maria A. Chiacchio,
  • Adriana Garozzo,
  • Emanuele Amata,
  • Giovanni Romeo and
  • Ugo Chiacchio

Beilstein J. Org. Chem. 2015, 11, 328–334, doi:10.3762/bjoc.11.38

Graphical Abstract
  • presence of NH4Cl, promotes an equilibrium process which starts from 11 and leads to a mixture of α- and β-anomers, via the intermediate oxonium ion 15 (path a) or 16 (path b) (Figure 3). As reported in similar systems [45], in the equilibrium mixture the β-anomer 11, thermodynamically more stable
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Published 09 Mar 2015

3α,5α-Cyclocholestan-6β-yl ethers as donors of the cholesterol moiety for the electrochemical synthesis of cholesterol glycoconjugates

  • Aneta M. Tomkiel,
  • Adam Biedrzycki,
  • Jolanta Płoszyńska,
  • Dorota Naróg,
  • Andrzej Sobkowiak and
  • Jacek W. Morzycki

Beilstein J. Org. Chem. 2015, 11, 162–168, doi:10.3762/bjoc.11.16

Graphical Abstract
  • in Scheme 3. The proposed formation of disteroidal oxonium ions accounts for an alkyl (aryl) group transfer from C-6 to C-3. Interestingly, the isomerization itself is not an electrochemical reaction. Electrooxidation is needed only to initiate the whole process, i.e., to generate the homoallylic
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Published 26 Jan 2015

A general metal-free approach for the stereoselective synthesis of C-glycals from unactivated alkynes

  • Shekaraiah Devari,
  • Manjeet Kumar,
  • Ramesh Deshidi,
  • Masood Rizvi and
  • Bhahwal Ali Shah

Beilstein J. Org. Chem. 2014, 10, 2649–2653, doi:10.3762/bjoc.10.277

Graphical Abstract
  • forming an oxonium ion intermediate, which is attacked by trimethylsilylacetylene to give the corresponding product (Scheme 3, reaction 2). The stereochemistry of the reaction products is possibly determined by the coordination between two π-electron orbitals of the oxocarbonium ion and the acetylene
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Published 12 Nov 2014

Silver and gold-catalyzed multicomponent reactions

  • Giorgio Abbiati and
  • Elisabetta Rossi

Beilstein J. Org. Chem. 2014, 10, 481–513, doi:10.3762/bjoc.10.46

Graphical Abstract
  • diastereoisomeric 1,2-dihydroisoquinolines 40 (Scheme 22) [60]. Iminium intermediate 28, generated in situ from the aldimine 27 under silver triflate catalysis is the usual electrophilic intermediate, whereas the nucleophile, in this case, is the oxonium ylide 39. The reaction resulted in the synthesis of highly
  • substituted 1,2-dihydroisoquinolines 40 characterized by the presence of an α-hydroxy/alkoxy-α-carboxylate carbon pendant. The oxonium ylide 39 was prepared by a well-known procedure involving a rhodium carbenoid intermediate, generated in situ from the corresponding diazoacetate 37 under Rh2(OAc)4 catalysis
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Published 26 Feb 2014

Gold(I)-catalyzed enantioselective cycloaddition reactions

  • Fernando López and
  • José L. Mascareñas

Beilstein J. Org. Chem. 2013, 9, 2250–2264, doi:10.3762/bjoc.9.264

Graphical Abstract
  • intermediates of type X by an intramolecular carbonyl group, followed by the ring closing of the resulting oxonium intermediate XI. The reaction occurs at low temperatures by using only 1 mol % of a phosphite-based gold catalyst. The enantioselective version, which is catalyzed by the DTBM-Segphos complex Au1
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Published 30 Oct 2013

The chemistry of isoindole natural products

  • Klaus Speck and
  • Thomas Magauer

Beilstein J. Org. Chem. 2013, 9, 2048–2078, doi:10.3762/bjoc.9.243

Graphical Abstract
  • using an intramolecular Diels–Alder reaction. The synthetic endeavor began with the conversion of dihydropyran 79 to the acetal 80 (Scheme 9). Activation of the anomeric position with tin(IV) chloride presumably led to the formation of the oxonium ion 81. This intermediate was envisioned to undergo a
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Published 10 Oct 2013

Gold-catalyzed intermolecular coupling of sulfonylacetylene with allyl ethers: [3,3]- and [1,3]-rearrangements

  • Jungho Jun,
  • Hyu-Suk Yeom,
  • Jun-Hyun An and
  • Seunghoon Shin

Beilstein J. Org. Chem. 2013, 9, 1724–1729, doi:10.3762/bjoc.9.198

Graphical Abstract
  • groups underwent smooth reactions (Table 2, entries 2 and 3). It is reasonable to assume that a bulky group R1 would decelerate the initial O-attack on the alkyne. However, once the Au-bound oxonium ion (A in Scheme 1) is formed, the resulting rearrangement seems to be facilitated by the presence of a
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Published 22 Aug 2013

Anionic cascade reactions. One-pot assembly of (Z)-chloro-exo-methylenetetrahydrofurans from β-hydroxyketones

  • István E. Markó and
  • Florian T. Schevenels

Beilstein J. Org. Chem. 2013, 9, 1319–1325, doi:10.3762/bjoc.9.148

Graphical Abstract
  • -exo-methylenetetrahydrofuran 42 is converted into the oxonium cation 43. Subsequent capture of this intermediate 43 by a second molecule of 42 can occur via two different pathways. The first one involves the addition of the enol ether function of 42 onto 43, leading to the creation of a new C–C bond
  • with concomitant generation of another oxonium species 47. Intramolecular capture of this electrophile by the pendant hydroxy substituent then delivers the spirocyclic adduct 48. Alternatively, reaction of the tertiary alcohol of 42 with the oxonium cation 43 affords the ketal 44. Protonation of the
  • may indeed be operational in these cases. Protonation of diene 56 leads to the oxonium ion 57, which undergoes a 1,4-addition of another 56 unit, affording the new cation 58. At this stage, two different pathways can be followed. Either carbocation 58 can lose a proton, generating the observed triene
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Published 03 Jul 2013

Synthesis of a novel chemotype via sequential metal-catalyzed cycloisomerizations

  • Bo Leng,
  • Stephanie Chichetti,
  • Shun Su,
  • Aaron B. Beeler and
  • John A. Porco Jr.

Beilstein J. Org. Chem. 2012, 8, 1338–1343, doi:10.3762/bjoc.8.153

Graphical Abstract
  • malonate substituent (Nu, 24a) to minimize steric interactions relative to 24b, leading to the observed diastereoselectivity (Scheme 3, inset) [23][24]. Subsequent cyclopropane formation through addition of the vinyl metal to the oxonium intermediate affords metallocarbenoid 26, which may then undergo a
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Published 20 Aug 2012

A concise synthesis of 3-(1-alkenyl)isoindolin-1-ones and 5-(1-alkenyl)pyrrol-2-ones by the intermolecular coupling reactions of N-acyliminium ions with unactivated olefins

  • Nianhong Lu,
  • Lihong Wang,
  • Zhanshan Li and
  • Wei Zhang

Beilstein J. Org. Chem. 2012, 8, 192–200, doi:10.3762/bjoc.8.21

Graphical Abstract
  • products 4 were isolated (Table 2, entries 2 and 8 and Table 3, entries 2 and 9) much like the ene-type adducts of oxonium ion with olefins [37][38]. This means that these alkenes may be envisioned as surrogates of their corresponding, more expensive and less atom-economical, allylsilane derivatives, which
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Published 06 Feb 2012

Dependency of the regio- and stereoselectivity of intramolecular, ring-closing glycosylations upon the ring size

  • Patrick Claude,
  • Christian Lehmann and
  • Thomas Ziegler

Beilstein J. Org. Chem. 2011, 7, 1609–1619, doi:10.3762/bjoc.7.189

Graphical Abstract
  • , entropy-reducing intramolecular cyclization step. Within the frame of an overall SN1 reaction, the cyclization step is regarded as the rate-determining step; therefore, the transition state for the nucleophilic addition to the glycosyl cyclic oxonium intermediate may allow for a rationalization of the
  • compared to its next highest diastereomer 6d, β(1→3), as documented in Figure 6. Nevertheless, a closer approximation to the real transition state involving the pyranose cyclic oxonium intermediate is possible within our calibrated force field approach: Figure 7 highlights the stereoelectronic course of
  • ? Figure 11 illustrates what we intuitively anticipated at the beginning of the discussion, namely that the aromatic stacking interactions have a remarkable influence on the course of an intramolecular cyclization reaction: If the precyclized (seco) cyclic oxonium ion is modeled as an approximation for its
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Published 01 Dec 2011

Amines as key building blocks in Pd-assisted multicomponent processes

  • Didier Bouyssi,
  • Nuno Monteiro and
  • Geneviève Balme

Beilstein J. Org. Chem. 2011, 7, 1387–1406, doi:10.3762/bjoc.7.163

Graphical Abstract
  • attack of the hydroxyl group onto the triple bond activated by a Pd(II) cationic complex, followed by a protodemetalation, which afforded the methylidenefuran 21. This reacts with the imine activated by the Pd(II) species through a Mannich-type process. Finally, addition of the phenol to the oxonium can
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Published 10 Oct 2011

Gold(I)-catalyzed synthesis of γ-vinylbutyrolactones by intramolecular oxaallylic alkylation with alcohols

  • Michel Chiarucci,
  • Mirko Locritani,
  • Gianpiero Cera and
  • Marco Bandini

Beilstein J. Org. Chem. 2011, 7, 1198–1204, doi:10.3762/bjoc.7.139

Graphical Abstract
  • ]. Subsequently, the direct nucleophilic attack by the carboxylate unit would lead to an oxonium intermediate III [50][51] that, after dealkylation, resulted in the final lactone 2. Control experiments have been performed to indentify the presence of a Brønsted acid cocatalysis in the ring-closing procedure (see
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Published 01 Sep 2011

Recent developments in gold-catalyzed cycloaddition reactions

  • Fernando López and
  • José L. Mascareñas

Beilstein J. Org. Chem. 2011, 7, 1075–1094, doi:10.3762/bjoc.7.124

Graphical Abstract
  • on an initial (3 + 2) dipolar cycloaddition between the carbonyl ylide IV and the alkene, followed by a ring expansion (1,2-alkyl migration) that is assisted by the oxy group and generates the oxonium intermediate V (Scheme 2). A final elimination process regenerates the catalyst and affords the
  • , followed by addition of the generated alkenyl metallic species to the α,β-unsaturated silyl oxonium moiety, to give a bicyclic carbene intermediate XVI [59]. These species, which do not incorporate an α-hydrogen atom that could participate in a 1,2-hydrogen shift process, evolve through a 1,2-alkyl
  • , attacking the gold–cyclopropyl carbene intermediate XIX to generate an oxonium cation species of type XX. Finally, a Prins-like cyclization renders the oxatricyclic product 28 and regenerates the gold(I) catalyst. Importantly, this strategy was successfully applied as a key step in the synthesis of
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Published 09 Aug 2011

Functionalization of anthracene: A selective route to brominated 1,4-anthraquinones

  • Kiymet Berkil Akar,
  • Osman Cakmak,
  • Orhan Büyükgüngör and
  • Ertan Sahin

Beilstein J. Org. Chem. 2011, 7, 1036–1045, doi:10.3762/bjoc.7.118

Graphical Abstract
  • in C2 and C3 induces the formation of a bridged-oxonium ion 20 as an intermediate of 17. Hydrolysis of hexabromide 6 can lead to three halohydrines (17, 21 and 22), two of which are symmetric (Scheme 5). Dihalohydrine 17 is expected to be a good precursor to corresponding arene oxides 23 as shown in
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Published 29 Jul 2011

Recent advances in the gold-catalyzed additions to C–C multiple bonds

  • He Huang,
  • Yu Zhou and
  • Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

Graphical Abstract
  • atoms to form the intermediates 26 or 27, which then rearrange to yield the oxonium intermediates 28 or 29, respectively. Gold(I)-catalyzed intramolecular cyclization of monopropargylic triols 32 has been reported to be a novel and mild approach [29] for producing olefin-containing spiroketals 33 (and
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Published 04 Jul 2011

When gold can do what iodine cannot do: A critical comparison

  • Sara Hummel and
  • Stefan F. Kirsch

Beilstein J. Org. Chem. 2011, 7, 847–859, doi:10.3762/bjoc.7.97

Graphical Abstract
  • majority of gold-catalyzed cyclization modes have involved initial carbon-heteroatom bond formation [7][10]. As a general rule, the nucleophilic attack of a carbonyl (or imine) group onto an alkyne activated by gold-complexation generates first an oxonium (iminium) ion species, the cationic character of
  • cyclic oxonium ion is produced in the first stage of the cascade via both gold- and iodonium-triggered cyclization. In both cases, the heterocyclization is followed by a 1,2-migration onto the oxonium ion, where the only difference is whether the final product bears a H or an I atom at the C4-position
  • such as 58 were treated with AuCl, the formation of cyclohexadienes was strongly favored, presumably due to the highly stabilized oxonium ion intermediates (path b). Essentially, these transformations are not viable with an iodonium source as they do not possess the ability to proceed through simple
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Published 22 Jun 2011

Synthetic applications of gold-catalyzed ring expansions

  • David Garayalde and
  • Cristina Nevado

Beilstein J. Org. Chem. 2011, 7, 767–780, doi:10.3762/bjoc.7.87

Graphical Abstract
  • (Scheme 22) [54]. In most cases trans products were favored. The reaction is proposed to proceed via the cyclopropyl carbene 73, which undergoes ring expansion to form the alkenyl–gold intermediate 74. Reaction of the latter with the oxonium cation produces 75, which upon gold departure forms tricycles 71
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Published 07 Jun 2011

Construction of cyclic enones via gold-catalyzed oxygen transfer reactions

  • Leping Liu,
  • Bo Xu and
  • Gerald B. Hammond

Beilstein J. Org. Chem. 2011, 7, 606–614, doi:10.3762/bjoc.7.71

Graphical Abstract
  • ; gold-catalyzed; oxonium; oxygen transfer; Review α,β-Unsaturated carbonyl derivatives are not only important building blocks in synthetic organic chemistry, but are also a significant motif in natural products and biologically active compounds [1][2][3][4][5][6][7][8]. The construction of the
  • produced β,γ-unsaturated bicyclic enones rather than their α,β-unsaturated counterparts. Yamamoto and co-workers proposed a [2 + 2] mechanism for their gold-catalyzed cyclization of alkynyl ketones (Scheme 3). In their mechanism, the carbonyl group attacks the gold activated triple bond to form an oxonium
  • -membered ring oxonium intermediate C than for the seven-membered ring oxonium A. This energetic preference is also observed in the stabilities of the oxoniums themselves, with C considerably more stable by 16.1 kcal/mol. The subsequent transformations are all computed to be feasible, with the barrier to [4
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Published 13 May 2011
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