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Search for "Brønsted acid" in Full Text gives 153 result(s) in Beilstein Journal of Organic Chemistry.

Enantioselective additions of copper acetylides to cyclic iminium and oxocarbenium ions

  • Jixin Liu,
  • Srimoyee Dasgupta and
  • Mary P. Watson

Beilstein J. Org. Chem. 2015, 11, 2696–2706, doi:10.3762/bjoc.11.290

Graphical Abstract
  • -catalyst. With the addition of chiral Brønsted acid co-catalyst 27, high yields and good to excellent levels of enantioselectivity were achieved in the addition of both aryl and aliphatic alkynes (Scheme 8B). The azomethine amine products 24 and 26 can be deprotected using SmI2. To our knowledge, this
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Published 22 Dec 2015

Latent ruthenium–indenylidene catalysts bearing a N-heterocyclic carbene and a bidentate picolinate ligand

  • Thibault E. Schmid,
  • Florian Modicom,
  • Adrien Dumas,
  • Etienne Borré,
  • Loic Toupet,
  • Olivier Baslé and
  • Marc Mauduit

Beilstein J. Org. Chem. 2015, 11, 1541–1546, doi:10.3762/bjoc.11.169

Graphical Abstract
  • -diisopropylphenyl)imidazolidin-2-ylidene) demonstrated excellent latent behaviour in ring closing metathesis (RCM) reaction and could be activated in the presence of a Brønsted acid. The versatility of the catalyst 4a was subsequently demonstrated in RCM, cross-metathesis (CM) and enyne metathesis reactions
  • , we proceeded to synthesize complex 4b, featuring the 5-bromo-2-picolinate moiety. Using a similar methodology, the desired complex was obtained with 42% yield. The activation of the new picolinic complex 4a was initially evaluated in the presence of trifluoroacetic acid (TFA), a Brønsted acid easy to
  • bulkier ancillary ligand SIPr, appeared as highly stable, well-defined species. These species were shown to activate in the presence of a Brønsted acid and precatalysts 2 and 4a showed an excellent latent behaviour. The best reaction rates were obtained in the RCM of DEDAM with complex 4a after activation
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Published 03 Sep 2015

Efficient deprotection of F-BODIPY derivatives: removal of BF2 using Brønsted acids

  • Mingfeng Yu,
  • Joseph K.-H. Wong,
  • Cyril Tang,
  • Peter Turner,
  • Matthew H. Todd and
  • Peter J. Rutledge

Beilstein J. Org. Chem. 2015, 11, 37–41, doi:10.3762/bjoc.11.6

Graphical Abstract
  • organic acid TFA or the inorganic acid HCl. These conditions are complementary to those previously reported for converting F-BODIPYs to the parent dipyrrins using either strong bases or Lewis acids. Compared to existing methods, the Brønsted acid conditions are relatively mild and operationally simple
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Published 09 Jan 2015

Galactan synthesis in a single step via oligomerization of monosaccharides

  • Marius Dräger and
  • Amit Basu

Beilstein J. Org. Chem. 2014, 10, 2658–2663, doi:10.3762/bjoc.10.279

Graphical Abstract
  • observations suggest that desilylation is most likely the result of transient Brønsted acid formation during the reaction and not due to fluoride ion generation. In an attempt to tune silyl ether deprotection rates and promote formation of longer oligomers, we examined the glycosylation of a bulkier TBDPS
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Published 13 Nov 2014

Facile synthesis of 1H-imidazo[1,2-b]pyrazoles via a sequential one-pot synthetic approach

  • András Demjén,
  • Márió Gyuris,
  • János Wölfling,
  • László G. Puskás and
  • Iván Kanizsai

Beilstein J. Org. Chem. 2014, 10, 2338–2344, doi:10.3762/bjoc.10.243

Graphical Abstract
  • isocyanides in the presence (5–30 mol %) of Lewis or Brønsted acid at ambient temperature or under heating (50–140 °C). The main disadvantages of this protocol involve long reaction times (3–18 hours) and requisite purification protocols (column chromatography and/or recrystallisation) besides limited
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Published 08 Oct 2014

Chiral phosphines in nucleophilic organocatalysis

  • Yumei Xiao,
  • Zhanhu Sun,
  • Hongchao Guo and
  • Ohyun Kwon

Beilstein J. Org. Chem. 2014, 10, 2089–2121, doi:10.3762/bjoc.10.218

Graphical Abstract
  • 2010, using the bifunctional chiral phosphine G1, bearing both Brønsted acid and Lewis base units, as the catalyst, asymmetric domino aza-MBH/aza-Michael reactions of activated alkenes and N-tosylimines with Michael acceptor moieties at their ortho positions were accomplished to give chiral 1,3
  • , both aryl and alkyl. The addition of a Brønsted acid to the reaction system slightly improved the yields and diastereocontrol. In addition, the resulting tetrahydropyridines could be transformed to more complex dihydroxylated piperidine derivatives. At almost the same time, an intramolecular variant of
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Published 04 Sep 2014

Synthesis of α-amino amidines through molecular iodine-catalyzed three-component coupling of isocyanides, aldehydes and amines

  • Praveen Reddy Adiyala,
  • D. Chandrasekhar,
  • Jeevak Sopanrao Kapure,
  • Chada Narsimha Reddy and
  • Ram Awatar Maurya

Beilstein J. Org. Chem. 2014, 10, 2065–2070, doi:10.3762/bjoc.10.214

Graphical Abstract
  • development of a mild, inexpensive and efficient catalytic protocol for the amidine synthesis is highly needed. Iodine is expected to act as a Lewis acid or Brønsted acid in methanol [20]. Apart from oxidation, catalytic iodine provides mild and efficient ways for the formation of C–C and C–N bonds [20]. As a
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Published 02 Sep 2014

Cyclization–endoperoxidation cascade reactions of dienes mediated by a pyrylium photoredox catalyst

  • Nathan J. Gesmundo and
  • David A. Nicewicz

Beilstein J. Org. Chem. 2014, 10, 1272–1281, doi:10.3762/bjoc.10.128

Graphical Abstract
  • hydroperoxides with pendant alkenes or alkynes have been developed. Selected examples include Pd(II)-catalyzed hydroalkoxylation reactions of unsaturated hydroperoxides [9], Au(I)-catalyzed endoperoxidation of alkynes [10] and Brønsted acid-catalyzed enantioselective acetalization/oxa-Michael addition cascade
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Published 03 Jun 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
  • reaction with the chloride ion released during the initial imine acylation. Finally, a combination between Brønsted acid and metal catalysis, promote the isomerization of V to oxazole 21. It is noteworthy, that the gold catalyst seemed to be essential only for the formation of the gold-acetylide
  • great chemical diversity of the products of MCRs. Moreover, imines can participate in MCRs as electrophilic or nucleophilic partners, azadienes, dienophiles and 1,3-dipoles. All these reactions may benefit from the presence of a Lewis acid, a Brønsted acid or a transition metal catalyst. Silver
  • . However, an alternative reaction pathway, involving a concerted [3 + 2] cycloaddition of 64 to the imine, cannot be ruled out. Additionally, the use of sterically demanding amines results in lower yields. It is noteworthy, that the same reactions performed in the presence of a weak Brønsted acid instead
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Published 26 Feb 2014

Secondary amine-initiated three-component synthesis of 3,4-dihydropyrimidinones and thiones involving alkynes, aldehydes and thiourea/urea

  • Jie-Ping Wan,
  • Yunfang Lin,
  • Kaikai Hu and
  • Yunyun Liu

Beilstein J. Org. Chem. 2014, 10, 287–292, doi:10.3762/bjoc.10.25

Graphical Abstract
  • equiv of p-TSA has been found to significantly improve the yield (Table 1, entry 14). This result may be attributed to the double activation effect involving both Lewis and Brønsted acid (see Scheme 3). With the optimal conditions in hand, we conducted the investigation on examining the application
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Published 29 Jan 2014

Studies on the interaction of isocyanides with imines: reaction scope and mechanistic variations

  • Ouldouz Ghashghaei,
  • Consiglia Annamaria Manna,
  • Esther Vicente-García,
  • Marc Revés and
  • Rodolfo Lavilla

Beilstein J. Org. Chem. 2014, 10, 12–17, doi:10.3762/bjoc.10.3

Graphical Abstract
  • respect, taking imine 1a (R1 = p-MeOC6H4; R2 = p-ClC6H4) and isocyanide 2a (R3 = t-Bu), we tested the standard reaction in THF, MeCN, and CH2Cl2 as solvents using a variety of Lewis and Brønsted acid activating agents (20–100 mol %) including: InCl3, Sc(OTf)3, AuCl3, AgOTf, GaCl3, NbCl5, camphorsulfonic
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Published 06 Jan 2014

New developments in gold-catalyzed manipulation of inactivated alkenes

  • Michel Chiarucci and
  • Marco Bandini

Beilstein J. Org. Chem. 2013, 9, 2586–2614, doi:10.3762/bjoc.9.294

Graphical Abstract
  • functionalization of alkenes rely on the use of “oxidative strategies” exploiting the [Au(I)/Au(III)] or [Au(I)Au(I)/Au(II)Au(II)] catalytic couples that can be accessed through the use of a suitable exogenous oxidant (Figure 2, path c) [9]. Last but not least, the potential role of Brønsted acid co-catalysis
  • process for the formation of new C–O bonds. In this direction numerous examples of metal and Brønsted-acid catalyzed condensations of alcohols, phenols and carboxylic acids to inactivated olefins have been reported [16]. Interestingly, He and co-workers compared the catalytic attitude of TfOH and
  • PPh3AuOTf in the addition of various nucleophiles to alkenes, demonstrating how the gold complex and triflic acid can exhibit complementary efficiency [17]. This finding suggests that although Brønsted acid co-catalysis is a possible competing process, under suitable conditions the gold-catalyzed pathway is
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Published 21 Nov 2013

A combined continuous microflow photochemistry and asymmetric organocatalysis approach for the enantioselective synthesis of tetrahydroquinolines

  • Erli Sugiono and
  • Magnus Rueping

Beilstein J. Org. Chem. 2013, 9, 2457–2462, doi:10.3762/bjoc.9.284

Graphical Abstract
  • the synthesis of tetrahydroquinolines from readily available 2-aminochalcones using a combination of photochemistry and asymmetric Brønsted acid catalysis. The photocylization and subsequent reduction was performed with catalytic amount of chiral BINOL derived phosphoric acid diester and Hantzsch
  • uniform irradiation through the entire reactor and the complete reaction medium, in comparison with reactions performed in conventional batch systems. Here we report the development of continuous-flow photochemical reaction in combination with asymmetric Brønsted acid catalysis for the synthesis of
  • source and catalytic amount of chiral Brønsted acid 3. The effect of temperature, flow rate and concentration on the reaction yield and enantioselectivity are summarized in Table 1. As shown in Table 1, performing the reaction in a pyrex test tube (i.d.: 12 mm; λ > 300 nm) with 1 mol % of Brønsted acid 3
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Published 13 Nov 2013

Silica sulfuric acid: a reusable solid catalyst for one pot synthesis of densely substituted pyrrole-fused isocoumarins under solvent-free conditions

  • Sudipta Pathak,
  • Kamalesh Debnath and
  • Animesh Pramanik

Beilstein J. Org. Chem. 2013, 9, 2344–2353, doi:10.3762/bjoc.9.269

Graphical Abstract
  •  2). When the reaction was carried out in aqueous solution under reflux the reaction did not proceed at all (Table 1, entry 1). Previous results showed that an activation by a Brønsted acid was necessary to carry out the reaction successfully [38]. Therefore, we screened various Brønsted acid
  • , both for aromatic and aliphatic amines. We restrained the reaction to using PEG–OSO3H as a Brønsted acid–surfactant combined catalyst in aqeous solution under refluxing conditions as well as under solvent-free conditions (Table 1, entries 7 and 8). Although under solvent-free conditions the required
  • chemical processes. Hence, we have carried out the synthesis by dissolving the substrate 7 and aniline in a minimum volume of chloroform, soaked them on the solid surface of solid Brønsted acid catalysts, such as silica gel and melamine sulfonic acid (MSA), dried the mixture under vacuum, and heated the
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Published 04 Nov 2013

Gold-catalyzed glycosidation for the synthesis of trisaccharides by applying the armed–disarmed strategy

  • Abhijeet K. Kayastha and
  • Srinivas Hotha

Beilstein J. Org. Chem. 2013, 9, 2147–2155, doi:10.3762/bjoc.9.252

Graphical Abstract
  • trisaccharide. Instead, disaccharide 3 (53%) and 1,6-anhydro sugar 5 (20%) were isolated as major products [37]. Interestingly, propargyl mannoside 1 (12%) along with benzyl glycoside 6 and lactol 7 were noticed in 5% and 4% yield, respectively (Scheme 1). The Brønsted acid (HBr) released from AuBr3 in the
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Published 18 Oct 2013

The chemistry of amine radical cations produced by visible light photoredox catalysis

  • Jie Hu,
  • Jiang Wang,
  • Theresa H. Nguyen and
  • Nan Zheng

Beilstein J. Org. Chem. 2013, 9, 1977–2001, doi:10.3762/bjoc.9.234

Graphical Abstract
  • independently discovered that the efficiency of the same Michael reaction was greatly improved in the presence of a Brønsted acid (Scheme 23) [90]. Some of the improvements included shorter reaction time, higher yields, and use of a weaker light source (CFL). The most effective acid catalysts, of which TFA was
  • Michael acceptors. Conjugated addition of α-amino radicals to Michael acceptors assisted by a Brønsted acid. Conjugated addition of α-amino radicals derived from anilines to Michael acceptors. Oxygen switch between two pathways involving α-amino radicals. Interception of α-amino radicals by
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Published 01 Oct 2013

One-step synthesis of pyridines and dihydropyridines in a continuous flow microwave reactor

  • Mark C. Bagley,
  • Vincenzo Fusillo,
  • Robert L. Jenkins,
  • M. Caterina Lubinu and
  • Christopher Mason

Beilstein J. Org. Chem. 2013, 9, 1957–1968, doi:10.3762/bjoc.9.232

Graphical Abstract
  • material. In the Bohlmann–Rahtz reaction, the use of a Brønsted acid catalyst allows Michael addition and cyclodehydration to be carried out in a single step without isolation of intermediates to give the corresponding trisubstituted pyridine as a single regioisomer in good yield. Furthermore, 3
  • continuous flow reactor examined the cyclodehydration of Bohlmann–Rahtz aminodienone intermediates in the presence of a Brønsted acid catalyst [44][45]. This relatively simple cyclization reaction was utilized previously as we had already established its facility under microwave irradiation and so it
  • = Ph) [51], in the presence of acetic acid as a Brønsted acid catalyst for transfer to flow processing. A range of conditions were investigated (Table 1) and, in each case, 1H NMR spectroscopic analysis of the crude reaction mixture revealed if unreacted starting materials were present. Microwave
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Published 30 Sep 2013

Gold(I)-catalysed one-pot synthesis of chromans using allylic alcohols and phenols

  • Eloi Coutant,
  • Paul C. Young,
  • Graeme Barker and
  • Ai-Lan Lee

Beilstein J. Org. Chem. 2013, 9, 1797–1806, doi:10.3762/bjoc.9.209

Graphical Abstract
  • , entries 8–10). Firstly, no reaction is observed in the absence of a catalyst (Table 1, entry 8). The Brønsted acid catalyst HNTf2 does form chroman 8, but in a poorer isolated yield (21%, Table 1, entry 9) and the silver salt [76] AgNTf2 as a catalyst does not provide any 8, yielding only 9 and 10 (Table
  •  1, entry 10). The former is consistent with literature reports that Brønsted acid-catalysed reactions give poor yields when the phenol is not para-substituted [19]. Therefore, it seems that the gold(I) catalyst is most efficient in catalysing the one-pot formation of chroman 8. With these results in
  • temperature (Table 2, entries 4, 7, 8 and 10). In contrast to the Brønsted acid procedure [19], the substitution position has limited effect on the efficiency of the gold-catalysed reaction, with p-cresol (5b), m-cresol (5c) and o-cresol (5d) all forming the desired chromans 8b–d in decent to good yields
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Published 04 Sep 2013

A Lewis acid-promoted Pinner reaction

  • Dominik Pfaff,
  • Gregor Nemecek and
  • Joachim Podlech

Beilstein J. Org. Chem. 2013, 9, 1572–1577, doi:10.3762/bjoc.9.179

Graphical Abstract
  • electrophile (Scheme 5). Reaction of silyl ether and nitrilium cation leads to a cationic N,O-bis(trimethylsilyl)imino ester, which is hydrolyzed to a carboxylic ester. Formation of the Brønsted acid trifluoromethanesulfonic acid is to be expected under these reaction conditions, but seems to have no influence
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Published 02 Aug 2013

Organocatalytic asymmetric selenofunctionalization of tryptamine for the synthesis of hexahydropyrrolo[2,3-b]indole derivatives

  • Qiang Wei,
  • Ya-Yi Wang,
  • Yu-Liu Du and
  • Liu-Zhu Gong

Beilstein J. Org. Chem. 2013, 9, 1559–1564, doi:10.3762/bjoc.9.177

Graphical Abstract
  • ]. These leading findings indicate that either Lewis base or Brønsted acid shows catalytic activity for the selenofunctionalization reaction. Since chiral phosphoric acids have been shown to be Brønsted acid/Lewis base bifunctional organocatalysts [29][30][31][32][33], we ask whether the chiral BINOL-based
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Published 01 Aug 2013

Re2O7-catalyzed reaction of hemiacetals and aldehydes with O-, S-, and C-nucleophiles

  • Wantanee Sittiwong,
  • Michael W. Richardson,
  • Charles E. Schiaffo,
  • Thomas J. Fisher and
  • Patrick H. Dussault

Beilstein J. Org. Chem. 2013, 9, 1526–1532, doi:10.3762/bjoc.9.174

Graphical Abstract
  • a Brønsted acid. Keywords: allylation; hemiacetal; O,O-acetal; O,S-thioacetal; peroxyacetal; Re2O7; S,S-acetal; Introduction The synthetically important conversions of hemiacetals to acetals, thioacetals, or homoallyl ethers are typically achieved through activation of the substrate with a strong
  • ], we needed to prepare a number of 3-alkoxy-1,2-dioxolanes. Brønsted acid-promoted etherification of hemiacetals (1,2-dioxolan-3-ols) required harsh conditions and proceeded in good yields only for unhindered alcohols [18]. We were curious whether Re2O7, a catalyst known to activate alcohols via a
  • ions [21][22]. As illustrated in Table 5, tetrahydrofuranol and tetrahydropyranol both undergo condensation with a simple thiol in the presence of Re2O7 to provide the monothioacetal in good yield; only traces of the S,S-dithioacetal were observed. The same reaction, when catalyzed by a Brønsted acid
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Published 30 Jul 2013

Thiourea-catalyzed Diels–Alder reaction of a naphthoquinone monoketal dienophile

  • Carsten S. Kramer and
  • Stefan Bräse

Beilstein J. Org. Chem. 2013, 9, 1414–1418, doi:10.3762/bjoc.9.158

Graphical Abstract
  • of one equivalent of Brønsted acid 8 had no effect (Table 2, entry 4), the addition of TADDOL (9) improved the reaction speed (Table 2, entry 5). By the use of Schreiner's catalyst 10 [7], the highest conversion speed was observed (Table 2, entry 6). After this finding, Jacobsen's thioureas 11 [13
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Published 12 Jul 2013

Mild and efficient cyanuric chloride catalyzed Pictet–Spengler reaction

  • Ashish Sharma,
  • Mrityunjay Singh,
  • Nitya Nand Rai and
  • Devesh Sawant

Beilstein J. Org. Chem. 2013, 9, 1235–1242, doi:10.3762/bjoc.9.140

Graphical Abstract
  • -dimethylaminobenzaldehyde. These aldehydes failed to produce the cyclized product in desired yield under conventional Brønsted acid catalysis and often produced the oxidized products under harsher reaction conditions. TCT under an inert atmosphere allowed for a clean reaction with a broad substrate scope and application
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Published 26 Jun 2013

Camera-enabled techniques for organic synthesis

  • Steven V. Ley,
  • Richard J. Ingham,
  • Matthew O’Brien and
  • Duncan L. Browne

Beilstein J. Org. Chem. 2013, 9, 1051–1072, doi:10.3762/bjoc.9.118

Graphical Abstract
  • with various solid-phase Brønsted acid catalysts in supercritical carbon dioxide (Figure 7), Poliakoff and co-workers studied the effect of varying the concentration of the organic reagent in the liquid CO2 solvent [46]. The high pressures required (100–400 bar) stipulated the use of a sealed reaction
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Published 31 May 2013

Gold-catalyzed oxycyclization of allenic carbamates: expeditious synthesis of 1,3-oxazin-2-ones

  • Benito Alcaide,
  • Pedro Almendros,
  • M. Teresa Quirós and
  • Israel Fernández

Beilstein J. Org. Chem. 2013, 9, 818–826, doi:10.3762/bjoc.9.93

Graphical Abstract
  • (Scheme 2). Adding a catalytic amount of Brønsted acid (PTSA) into the reaction system did slightly improve the yield of 3a. Solvent screening demonstrated that dichloromethane was the best choice in the reaction. As revealed in Scheme 2, a variety of allenic carbamates 2 were also suitable for such
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Published 26 Apr 2013
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