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Search for "carbenes" in Full Text gives 168 result(s) in Beilstein Journal of Organic Chemistry.

Reactivity studies of pincer bis-protic N-heterocyclic carbene complexes of platinum and palladium under basic conditions

  • David C. Marelius,
  • Curtis E. Moore,
  • Arnold L. Rheingold and
  • Douglas B. Grotjahn

Beilstein J. Org. Chem. 2016, 12, 1334–1339, doi:10.3762/bjoc.12.126

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  • dibasic complex 8. Keywords: NHC; 15N NMR spectroscopy; palladium; platinum; protic N-heterocyclic carbene; Introduction N-Heterocyclic carbenes (NHCs) have been extensively researched for a number of purposes since 1991 when Arduengo first isolated free NHCs [1][2][3]. NHCs as ligands have been known
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Published 28 Jun 2016

On the mechanism of imine elimination from Fischer tungsten carbene complexes

  • Philipp Veit,
  • Christoph Förster and
  • Katja Heinze

Beilstein J. Org. Chem. 2016, 12, 1322–1333, doi:10.3762/bjoc.12.125

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  • complexes [16][17]. First representatives of multimetal carbene complexes M(CO)5(1R) bear α-ferrocenyl alkoxy carbenes :C(OR)Fc (1R, M = Cr, Mo, W; R = Me, Et; Fc = ferrocenyl) [18][19][20][21][22]. Nucleophilic substitution of the alkoxy substituent OR by amines gives access to α-ferrocenylamino Fischer
  • chromium (by py or CO) for Cr(CO)5(E/Z-4) and Cr(CO)5(Z-6). Both pathways are compatible with the formation of the metal-containing products fac-[Cr(CO)3(py)3] and Cr(CO)6 by dissociation of the imines E-5 or E-7 or by dissociation of the carbenes E-4 or E-6, respectively (Scheme 1b,c) [42][44]. The
  • (pathway 1b, Scheme 3), respectively. In the latter case, Z-3 isomerizes to the thermodynamically preferred isomer E-3. The second pathway (carbene elimination–migration) starts with the elimination of the carbenes E-2 or Z-2 followed by an 1,2-H shift to give the imines E-3 (pathway 2a, Scheme 3) or Z-3
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Published 27 Jun 2016

Catalytic asymmetric synthesis of biologically important 3-hydroxyoxindoles: an update

  • Bin Yu,
  • Hui Xing,
  • De-Quan Yu and
  • Hong-Min Liu

Beilstein J. Org. Chem. 2016, 12, 1000–1039, doi:10.3762/bjoc.12.98

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  • constructing biologically important spirooxindoles. In addition to the above mentioned metal- and organocatalyzed asymmetric synthesis of 3-hydroxyoxindoles, Zhao et al. reported a complementary strategy that employed the chiral acylazolium species (prepared from aldehydes and N-heterocycle carbenes) to
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Published 18 May 2016

The synthesis of functionalized bridged polycycles via C–H bond insertion

  • Jiun-Le Shih,
  • Po-An Chen and
  • Jeremy A. May

Beilstein J. Org. Chem. 2016, 12, 985–999, doi:10.3762/bjoc.12.97

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  • via C–H bond insertion by carbenes and nitrenes. Applications to natural product synthesis, a description of the essential elements in substrate-controlled reactions, and mechanistic details of transformations are presented. Overall, these transformations allow the construction of important ring
  • 1 or 3). This review highlights strategies that leverage C–H bond insertion by carbenes and nitrenes to construct bridged polycycles. This key bond-forming event may construct the bridged ring, or it may construct an additional ring fused to an existing bridged bicycle to synthesize the bridged
  • have organized this review by the catalyst used, with free carbenes first, followed by Cu, Rh, Au, Pt, and then W-catalyzed reactions. Review Metal-free reactions While transition metal catalysis has seen widespread adoption for carbene and nitrene reactions, it is not necessary for a controlled
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Published 17 May 2016

Enantioselective carbenoid insertion into C(sp3)–H bonds

  • J. V. Santiago and
  • A. H. L. Machado

Beilstein J. Org. Chem. 2016, 12, 882–902, doi:10.3762/bjoc.12.87

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  • carbenoid was reported in 1952 by Peter Yates, although the author does not specifically use the term carbenoid, but – carbene–copper complex (Scheme 1) [3]. In his opinion, the copper catalyst promotes the decomposition of diazoketones to afford "free carbenes", the chemical intermediates responsible for
  • term "carbenoid", the work does not present the formation of a copper carbenoid intermediate. It only suggests an insertion reaction occurring through free carbenes with copper working only as a catalyst to promote the carbene formation. In 1985, Taber and coworkers reported the synthesis of (+)-α
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Published 04 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

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  • Interdisciplinary Science and Technology,Trivandrum 695 019, India.; Fax: +91 471 2491712; Tel: +91 471 2490406 10.3762/bjoc.12.47 Abstract N-Heterocyclic carbenes (NHCs) have emerged as a powerful class of organocatalysts that mediate a variety of organic transformations. The Benzoin reaction constitutes one of
  • ; benzoin reaction; N-heterocyclic carbenes; organocatalysis; umpolung; Introduction The benzoin reaction (or condensation) is named after the product it furnishes via a catalytic assembly of two molecules of aromatic aldehydes. One molecule of the aldehyde functions as an acyl anion and the other as a
  • -heterocyclic carbenes (NHCs) are the two main classes of catalysts that are known to mediate benzoin reactions. This review focuses on the recent advancements made in the area of NHC-catalysed benzoin reactions. Historically, the first benzoin reaction was reported by Wöhler and Liebig in 1832. They discovered
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Published 09 Mar 2016

Scope and limitations of the dual-gold-catalysed hydrophenoxylation of alkynes

  • Adrián Gómez-Suárez,
  • Yoshihiro Oonishi,
  • Anthony R. Martin and
  • Steven P. Nolan

Beilstein J. Org. Chem. 2016, 12, 172–178, doi:10.3762/bjoc.12.19

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  • in unsymmetrical alkynes can help to achieve high regioselectivity in the hydrophenoxylation. Keywords: cooperative catalysis; gold catalysis; hydrophenoxylation; N-heterocyclic carbene; vinyl ethers; Introduction During the last 30 years, N-heterocyclic carbenes (NHCs) have evolved from mere
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Published 01 Feb 2016

Versatile deprotonated NHC: C,N-bridged dinuclear iridium and rhodium complexes

  • Albert Poater

Beilstein J. Org. Chem. 2016, 12, 117–124, doi:10.3762/bjoc.12.13

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  • ; iridium; isomerization; N-heterocyclic carbene; rhodium; Introduction In the framework of organometallic chemistry, N-heterocyclic carbenes (NHC) centre a well stablished class of relatively new ligands since in 1991 Arduengo and collaborators isolated the first stable NHC of the imidazole type with
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Published 22 Jan 2016

N-Methylphthalimide-substituted benzimidazolium salts and PEPPSI Pd–NHC complexes: synthesis, characterization and catalytic activity in carbon–carbon bond-forming reactions

  • Senem Akkoç,
  • Yetkin Gök,
  • İlhan Özer İlhan and
  • Veysel Kayser

Beilstein J. Org. Chem. 2016, 12, 81–88, doi:10.3762/bjoc.12.9

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  • with 4-chlorotoluene. Keywords: arylation; benzimidazolium salts; catalysis; N-heterocyclic carbene; PEPPSI complex; Suzuki–Miyaura cross-coupling reaction; Introduction The use of N-heterocyclic carbenes (NHCs) as ligands was started by Wanzlick [1] and Öfele [2] almost fifty years ago. There have
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Published 15 Jan 2016

Effective immobilisation of a metathesis catalyst bearing an ammonium-tagged NHC ligand on various solid supports

  • Krzysztof Skowerski,
  • Jacek Białecki,
  • Stefan J. Czarnocki,
  • Karolina Żukowska and
  • Karol Grela

Beilstein J. Org. Chem. 2016, 12, 5–15, doi:10.3762/bjoc.12.2

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  • metathesis and subsequent reduction of the obtained double bond in one pot. Keywords: catalysis; immobilisation; N-heterocyclic carbenes; olefin metathesis; ruthenium; Introduction Over the past decade olefin metathesis has undergone a grand development. The design of stable and active ruthenium-based
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Published 05 Jan 2016

Pyridylidene ligand facilitates gold-catalyzed oxidative C–H arylation of heterocycles

  • Kazuhiro Hata,
  • Hideto Ito,
  • Yasutomo Segawa and
  • Kenichiro Itami

Beilstein J. Org. Chem. 2015, 11, 2737–2746, doi:10.3762/bjoc.11.295

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  • strongest electron-donating N-heterocyclic carbenes, resulted in the rate acceleration of the C–H arylation reaction of heterocycles over conventional ligands such as triphenylphosphine and a classical N-heterocyclic carbene. In situ observation and isolation of the 2-pyridylidene-gold(III) species, as well
  • -catalyzed reactions, phosphines, N-heterocyclic carbenes, pyridines and salen ligands have been applied as ligands for controlling the stability of catalysts, and chemo-, regio- and enantioselectivities of the reactions [31][32][33][34][35][36]. Recent advances in the gold-catalyzed reactions are
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Published 28 Dec 2015

Direct estimate of the internal π-donation to the carbene centre within N-heterocyclic carbenes and related molecules

  • Diego M. Andrada,
  • Nicole Holzmann,
  • Thomas Hamadi and
  • Gernot Frenking

Beilstein J. Org. Chem. 2015, 11, 2727–2736, doi:10.3762/bjoc.11.294

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  • -Nancy, France 10.3762/bjoc.11.294 Abstract Fifteen cyclic and acylic carbenes have been calculated with density functional theory at the BP86/def2-TZVPP level. The strength of the internal X→p(π) π-donation of heteroatoms and carbon which are bonded to the C(II) atom is estimated with the help of NBO
  • calculations and with an energy decomposition analysis. The investigated molecules include N-heterocyclic carbenes (NHCs), the cyclic alkyl(amino)carbene (cAAC), mesoionic carbenes and ylide-stabilized carbenes. The bonding analysis suggests that the carbene centre in cAAC and in diamidocarbene have the
  • weakest X→p(π) π-donation while mesoionic carbenes possess the strongest π-donation. Keywords: bonding analysis; N-heterocyclic carbenes; π-donation; Introduction Since the isolation and unambiguous characterization of imidazol-2-ylidene by Arduengo in 1991 [1], the chemistry of stable singlet carbenes
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Published 24 Dec 2015

Rhodium, iridium and nickel complexes with a 1,3,5-triphenylbenzene tris-MIC ligand. Study of the electronic properties and catalytic activities

  • Carmen Mejuto,
  • Beatriz Royo,
  • Gregorio Guisado-Barrios and
  • Eduardo Peris

Beilstein J. Org. Chem. 2015, 11, 2584–2590, doi:10.3762/bjoc.11.278

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  • addition reaction of arylboronic acids to α,β-unsaturated ketones. Keywords: arylation of unsaturated ketones; mesoionic carbenes; nickel; iridium; rhodium; Introduction Highly symmetrical poly-NHCs are a very interesting type of ligands, because they allow the preparation of a variety of supramolecular
  • the addition reaction of arylboronic acids to 2-cyclohexen-1-one, where it showed good activity. The same ligand was also used for the preparation of nanometer-sized cylinder-like structures of Cu, Ag and Au [13]. As mesoionic carbenes (MICs) are known to be stronger electron donors compared to NHCs
  • which the reported TEP was 2045 cm−1, therefore suggesting that the tris-MIC ligand B is a stronger electron donor than ligand A. However, this comparison must be taken with care, because the tris-carbene ligands A and B, not only differ in the nature of their carbenes (MIC vs NHC), but also in their
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Published 14 Dec 2015

N-Heterocyclic carbenes

  • Steven P. Nolan

Beilstein J. Org. Chem. 2015, 11, 2474–2475, doi:10.3762/bjoc.11.268

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  • Steven P. Nolan Chemistry Department, College of Science, King Saud University, Riyadh 11451, Saudi Arabia 10.3762/bjoc.11.268 The N-heterocyclic carbenes (NHC) now hold a preferred-ligand status in organic and organometallic chemistry. Their role in catalysis continues to grow. When the
  • editorial staff at the Beilstein Journal of Organic Chemistry contacted me to act as a guest editor for the thematic series “N-Heterocyclic carbenes”, I was more than happy to accept what appeared to me to be a simple and exciting endeavor. Indeed, the job was made simple as the number of research groups
  • seminal work of Bertrand [1] and Arduengo [2] (and mostly post-1994–1995) the field has underwent fantastic advances. Carbenes such as 1,3-dimesityl-1,3-dihydro-2H-imidazol-2-ylidene (IMes) and the 2,6-diisopropylphenyl analogue (IPr) have become commonplace, replacing tertiary phosphanes as modifying
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Published 07 Dec 2015

Copper-catalyzed stereoselective conjugate addition of alkylboranes to alkynoates

  • Takamichi Wakamatsu,
  • Kazunori Nagao,
  • Hirohisa Ohmiya and
  • Masaya Sawamura

Beilstein J. Org. Chem. 2015, 11, 2444–2450, doi:10.3762/bjoc.11.265

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  • as PPh3 and PCy3 or the DPPE bisphopshine was also effective in promotion of the reaction, but resulted in a reduced stereoselectivity (Table 1, entries 2–4). No reaction occurred with N-heterocyclic carbenes (NHC) such as IMes or IPr (Table 1, entries 5 and 6). The reaction with (IMes)CuCl or (IPr
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Published 04 Dec 2015

Copper-catalyzed asymmetric conjugate addition of organometallic reagents to extended Michael acceptors

  • Thibault E. Schmid,
  • Sammy Drissi-Amraoui,
  • Christophe Crévisy,
  • Olivier Baslé and
  • Marc Mauduit

Beilstein J. Org. Chem. 2015, 11, 2418–2434, doi:10.3762/bjoc.11.263

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  • (CuTC) and (R)-Binap L4, which afforded the desired final products bearing two stereogenic centers with excellent diastereoselectivies (93–97%). N-Heterocyclic carbenes (NHCs) have emerged, in these last two decades, as a powerful and versatile class of ligands, and appeared to be potent in many
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Published 03 Dec 2015

Efficient synthetic protocols for the preparation of common N-heterocyclic carbene precursors

  • Morgan Hans,
  • Jan Lorkowski,
  • Albert Demonceau and
  • Lionel Delaude

Beilstein J. Org. Chem. 2015, 11, 2318–2325, doi:10.3762/bjoc.11.252

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  • N-heterocyclic carbenes (NHCs) have become a staple of modern synthetic chemistry [3][4][5][6][7]. Over the past twenty five years, they have evolved from laboratory curiosities to ubiquitous ancillary ligands, not only for all the transition metals whether in high or low oxidation state [8][9][10
  • are easily accessible via the deprotonation of imidazolium or imidazolinium salts with a strong base (Scheme 1, path A) [26][30]. The reaction is often carried out in situ to avoid the isolation of air- and moisture-sensitive free carbenes. Thus, the mixture of an imidazol(in)ium salt and a base
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Published 25 Nov 2015

Convenient preparation of high molecular weight poly(dimethylsiloxane) using thermally latent NHC-catalysis: a structure-activity correlation

  • Stefan Naumann,
  • Johannes Klein,
  • Dongren Wang and
  • Michael R. Buchmeiser

Beilstein J. Org. Chem. 2015, 11, 2261–2266, doi:10.3762/bjoc.11.246

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  • of Textile Chemistry and Chemical Fibers, Körschtalstrasse 26, D-73770 Denkendorf, Germany 10.3762/bjoc.11.246 Abstract The polymerization of octamethylcyclotetrasiloxane (D4) is investigated using several five-, six- and seven-membered N-heterocyclic carbenes (NHCs). The catalysts are delivered in
  • , 1.6 < ÐM < 2.5) in yields >95%, using low catalyst loadings (0.2–0.1 mol %). Furthermore, the results suggest that a nucleophilic, zwitterionic mechanism is in operation, in preference to purely anionic polymerization. Keywords: latency; N-heterocyclic carbenes; ring-opening organocatalysis
  • ; polymerization; polysiloxanes; Introduction N-Heterocyclic carbenes (NHCs) [1][2][3] have had a resounding impact on organopolymerization [4][5] during the past fifteen years. Considerable research effort has steadily deepened the mechanistic understanding of the polymerization pathways open to NHCs, while the
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Published 20 Nov 2015

Half-sandwich nickel(II) complexes bearing 1,3-di(cycloalkyl)imidazol-2-ylidene ligands

  • Johnathon Yau,
  • Kaarel E. Hunt,
  • Laura McDougall,
  • Alan R. Kennedy and
  • David J. Nelson

Beilstein J. Org. Chem. 2015, 11, 2171–2178, doi:10.3762/bjoc.11.235

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  • -coupling; N-heterocyclic carbenes; nickel; Introduction Nickel catalysis is currently an area of great interest, due to the potential for nickel to replace palladium in some catalytic processes, as well as its ability to perform a much wider range of reactions [1]. Nickel complexes bearing N-heterocyclic
  • carbenes (NHCs) [2] are an interesting class of catalysts [3][4], due to the fascinating characteristics of NHC ligands, which can be designed to have a wide range of steric and electronic properties [5][6][7]. Nickel catalysts of the form [Ni(Cp)X(NHC)] have been shown to be versatile and relatively easy
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Published 12 Nov 2015

Olefin metathesis in air

  • Lorenzo Piola,
  • Fady Nahra and
  • Steven P. Nolan

Beilstein J. Org. Chem. 2015, 11, 2038–2056, doi:10.3762/bjoc.11.221

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  • limits even further. As seen in this review, conducting metathesis-type reactions in air, in the presence of water and under high temperature has become more concrete, with several groups leading the charge [62][86]. NHC-Ruthenium complexes and widely used NHC carbenes. Scope of RCM reactions with
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Published 30 Oct 2015

Synthesis of quinoline-3-carboxylates by a Rh(II)-catalyzed cyclopropanation-ring expansion reaction of indoles with halodiazoacetates

  • Magnus Mortén,
  • Martin Hennum and
  • Tore Bonge-Hansen

Beilstein J. Org. Chem. 2015, 11, 1944–1949, doi:10.3762/bjoc.11.210

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  • transition metal-catalyzed C–H functionalization by diazo compounds [5][6][7][8]. The reactions of indoles with electrophilic metal-bound carbenes, or carbenoids, generated from diazo compounds, takes place under mild reaction conditions. The reaction has been studied for the three principle classes of
  • many of the reactions between indoles and metal-bound carbenes are unclear [5][6][7][8]. We have for some time worked with halodiazoacetates and studied their reactivity in cyclopropanation reactions [17], C–H insertion and Si–H insertion reactions [18]. Halodiazoacetates can be made quantiatively and
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Published 20 Oct 2015

Influence of bulky yet flexible N-heterocyclic carbene ligands in gold catalysis

  • Alba Collado,
  • Scott R. Patrick,
  • Danila Gasperini,
  • Sebastien Meiries and
  • Steven P. Nolan

Beilstein J. Org. Chem. 2015, 11, 1809–1814, doi:10.3762/bjoc.11.196

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  • transformations has been investigated. Keywords: catalysis; flexible and bulky ligands; gold; ligand design; N-heterocyclic carbenes; Introduction Homogeneous gold catalysis has witnessed an exponential growth in the last 15 years [1][2][3][4][5][6][7][8][9][10][11][12]. Gold complexes have been shown to be
  • efficient catalysts in a wide variety of transformations [1][2][3][4][5][6][7][8][9][10][11][12]. N-heterocyclic carbenes (NHC) have attracted particular attention as ancillary ligands due to their donating properties and steric hindrance [13][14][15][16][17][18][19][20]. These can be easily tuned by
  • modifying the architecture of the imidazole ring, typically, by changing the N-substituents or the backbone [13][14][15][16][17][18][19][20]. One of our research interests is the study of the electronic and steric properties of new N-heterocyclic carbenes and their influence in catalysis upon coordination
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Published 02 Oct 2015

Cross-metathesis of polynorbornene with polyoctenamer: a kinetic study

  • Yulia I. Denisova,
  • Maria L. Gringolts,
  • Alexander S. Peregudov,
  • Liya B. Krentsel,
  • Ekaterina A. Litmanovich,
  • Arkadiy D. Litmanovich,
  • Eugene Sh. Finkelshtein and
  • Yaroslav V. Kudryavtsev

Beilstein J. Org. Chem. 2015, 11, 1796–1808, doi:10.3762/bjoc.11.195

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  • -stage model. At the first stage of the reaction all Ru-benzylidene carbenes are transformed into Ru-polyoctenamers within an hour, while the polymer molar mass is considerably decreased. The second stage actually including interpolymeric reactions proceeds much slower and takes one day or more to
  • achieve a random copolymer of norbornene and cyclooctene. Its rate is limited by the interaction of polyoctenamer-bound carbenes with polynorbornene units, which is hampered, presumably due to steric reasons. Polynorbornene-bound carbenes are detected in very low concentrations throughout the whole
  • alternating dyad content in the NB-COE copolymer. Such dyads are formed via the reactions of PNB-bound carbenes with COE units and, vice versa, of PCOE-bound carbenes with NB units. The above kinetic model for the separate reactions of PCOE and PNB with Gr-1 is extended, which makes it possible to outline the
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Published 01 Oct 2015

Synthesis and structures of ruthenium–NHC complexes and their catalysis in hydrogen transfer reaction

  • Chao Chen,
  • Chunxin Lu,
  • Qing Zheng,
  • Shengliang Ni,
  • Min Zhang and
  • Wanzhi Chen

Beilstein J. Org. Chem. 2015, 11, 1786–1795, doi:10.3762/bjoc.11.194

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  • carbenes (NHCs) have been recognized as a class of strong donating ligands which can stabilize various metal complexes of catalytic importance. Transition metal complexes bearing NHCs are more stable to air, moisture, heat, and tolerant toward oxidation compared to phosphine ligands [1][2][3][4][5][6][7
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Published 30 Sep 2015

Fe(II)/Et3N-Relay-catalyzed domino reaction of isoxazoles with imidazolium salts in the synthesis of methyl 4-imidazolylpyrrole-2-carboxylates, its ylide and betaine derivatives

  • Ekaterina E. Galenko,
  • Olesya A. Tomashenko,
  • Alexander F. Khlebnikov,
  • Mikhail S. Novikov and
  • Taras L. Panikorovskii

Beilstein J. Org. Chem. 2015, 11, 1732–1740, doi:10.3762/bjoc.11.189

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  • -alkoxycarbonylpyrrol-3-ylimidazolium salts 1 attracted our attention as the potential precursors of ylides 2, which in principle could be in equilibrium with N-heterocyclic carbenes (NHC) 3. Furthermore, hydrolysis of 2 could provide an easy access to unknown carboxy-substituted ylides 4, and then could potentially be
  • in the equilibrium with N-heterocyclic carbenes 5 and betaine 6 (Scheme 1). Interplay between N-heterocyclic carbenes, heterocyclic betaines and ylides is currently intensively investigated as a promising route for tuning NHC for specific use. This topic was extensively reviewed [10][11][12][13][14
  • , ylides 2 can potentially be in tautomeric equilibrium with N-heterocyclic carbenes 3. No signals characteristic for carbenes 3a–i, however, were found in the NMR spectra of compound 2a–i. According to the DFT calculations mesomeric electron-donating substituents R2 in the pyrrole ring (Table 3, cf
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Published 24 Sep 2015
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