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

• gold-catalyzed synthesis of dihydrofuran-3-ones 63, in which terminal alkynes 62 were used as equivalents of α-diazo ketones to generate α-oxo gold carbenes (Scheme 12) [37]. The α-oxo gold carbenes were produced via gold-catalyzed intermolecular oxidation of 62. This provides improved synthetic

The role of silver additives in gold-mediated C–H functionalisation

• Scott R. Patrick,
• Ine I. F. Boogaerts,
• Sylvain Gaillard,
• Alexandra M. Z. Slawin and
• Steven P. Nolan

Beilstein J. Org. Chem. 2011, 7, 892–896, doi:10.3762/bjoc.7.102

• complexes bearing N-heterocyclic carbenes (NHC) [9][10] as supporting ligands has enabled the isolation of a “golden synthon”, [Au(OH)(IPr)] 1 (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), that is able to participate in metalation reactions with aromatic C–H bonds (Scheme 1) [11]. The reactivity

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

• cyclization events [51]. 1-(1-Alkynyl)cyclopropyl ketones 56 proved to be versatile building blocks for this purpose and gave, in the presence of indoles 57 as dipolarophiles, tetracyclic furans 58 in excellent yields (Scheme 20, reaction 1). NHC carbenes are preferred as ancillary ligands on the metal center

• 88 upon cyclopropyl ring expansion. Nevado and co-workers [59] have also recently used cyclopropyl intermediates, generated in situ via alkene cyclopropanations mediated by gold carbenes, for the stereocontrolled synthesis of 5- and 7-membered-rings (Scheme 27). This method was subsequently applied

When cyclopropenes meet gold catalysts

• Frédéric Miege,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2011, 7, 717–734, doi:10.3762/bjoc.7.82

• in a variety of gold-catalyzed reactions. The different contributions in this growing research area are summarized in this review. Keywords: cyclopropenes; gold carbenes; gold catalysis; gold-stabilized allylic cations; ring-opening; Review Introduction Homogeneous gold catalysis has become a

• gold-carbon order in the so-called organogold carbenoids. In the broad repertoire of gold-catalyzed organic transformations, gold-stabilized carbocations or, more often gold carbenes, can be found as intermediates in proposed mechanistic pathways, but the true nature of the organogold species had been

• a matter of debate [27]. Structural considerations: Gold-stabilized carbocations or gold carbenes? In 2008, Fürstner et al. took advantage of the ring-opening of 3,3-disubstituted cyclopropenes to generate organogold species and characterize them by NMR spectroscopy [16]. Whereas, 3,3

Gold-catalyzed regioselective oxidation of terminal allenes: formation of α-methanesulfonyloxy methyl ketones

• Yingdong Luo,
• Guozhu Zhang,
• Erik S. Hwang,
• Thomas A. Wilcoxon and
• Liming Zhang

Beilstein J. Org. Chem. 2011, 7, 596–600, doi:10.3762/bjoc.7.69

• ][13][14][15][16][17] or via allenes generated in situ [18][19][20][21]. We have recently shown that highly reactive gold carbenes can be generated from alkynes via gold-promoted intermolecular oxidation by pyridine/quinoline N-oxides [22][23][24][25], making benign alkynes effective surrogates of

Air-stable, recyclable, and time-efficient diphenylphosphinite cellulose-supported palladium nanoparticles as a catalyst for Suzuki–Miyaura reactions

• Qingwei Du and
• Yiqun Li

Beilstein J. Org. Chem. 2011, 7, 378–385, doi:10.3762/bjoc.7.48

• ], N-heterocyclic carbenes [13][14][15], P,O-based ligands [16], bis(thiourea) ligands [17], and thiosemicarbazone [18], etc. However, the separation of the catalyst and ligands from the final product is problematic. In this regard, studies on heterogeneous catalysts have drawn much attention because

Studies on Pd/NiFe₂O₄ catalyzed ligand-free Suzuki reaction in aqueous phase: synthesis of biaryls, terphenyls and polyaryls

• Sanjay R. Borhade and
• Suresh B. Waghmode

Beilstein J. Org. Chem. 2011, 7, 310–319, doi:10.3762/bjoc.7.41

• of phosphorous ligands. Efforts have been made to enhance the catalytic activity by the use of various ligands containing nitrogen or sulfur, as well as phosphines, salen and N-heterocyclic carbenes in traditional organic solvents [12][13][14][15][16][17][18][19]. However, the problems associated

Ene–yne cross-metathesis with ruthenium carbene catalysts

• Cédric Fischmeister and
• Christian Bruneau

Beilstein J. Org. Chem. 2011, 7, 156–166, doi:10.3762/bjoc.7.22

• , are reviewed in this article. In addition, the use of bio-resourced olefinic substrates is presented. Keywords: catalysis; cross-metathesis; enyne; fatty acid esters; ruthenium; Introduction The interaction of alkyne triple bonds with metal carbenes or metal vinylidene species was already known

Recent advances in the development of alkyne metathesis catalysts

• Xian Wu and
• Matthias Tamm

Beilstein J. Org. Chem. 2011, 7, 82–93, doi:10.3762/bjoc.7.12

• starts from N-heterocyclic carbenes 1 which react with trimethylsilyl azide to afford 2-trimethylsilyliminoimidazolines 2. After treatment with methanol, the corresponding imidazolin-2-imines 3 can be conveniently isolated [60]. Deprotonation by alkyl lithium reagents leads to imidazolin-2-iminato

The catalytic performance of Ru–NHC alkylidene complexes: PCy₃ versus pyridine as the dissociating ligand

• Stefan Krehl,
• Diana Geißler,
• Sylvia Hauke,
• Oliver Kunz,
• Lucia Staude and
• Bernd Schmidt

Beilstein J. Org. Chem. 2010, 6, 1188–1198, doi:10.3762/bjoc.6.136

• catalysts show similar activity in cross metathesis reactions. Keywords: homogeneous catalysis; N-heterocyclic carbenes; olefin metathesis; pyridine ligand; Ruthenium carbene complexes; Introduction Over the past two decades, the olefin metathesis reaction became one of the most important C–C-bond forming

• reactions in organic synthesis [1]. The elucidation of the crucial role of metal carbenes by Chauvin [2] and the development of stable and defined precatalysts for homogeneously catalyzed reactions by Schrock [3] and Grubbs [4] paved the way for this development. Since then, molybdenum- [5] and ruthenium

• propargylic alcohols as alkylidene precursors [10], which resulted in the synthesis of a first generation analogue C with an indenylidene ligand [11][12]. A landmark in the evolution of Ru-metathesis catalysts was the introduction of alkylidene complexes bearing N-heterocyclic carbenes (NHC) [13][14][15], in

Backbone tuning in indenylidene–ruthenium complexes bearing an unsaturated N-heterocyclic carbene

• César A. Urbina-Blanco,
• Xavier Bantreil,
• Hervé Clavier,
• Alexandra M. Z. Slawin and
• Steven P. Nolan

Beilstein J. Org. Chem. 2010, 6, 1120–1126, doi:10.3762/bjoc.6.128

• 10.3762/bjoc.6.128 Abstract The steric and electronic influence of backbone substitution in IMes-based (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) N-heterocyclic carbenes (NHC) was probed by synthesizing the [RhCl(CO)2(NHC)] series of complexes to quantify experimentally the Tolman

• parameters. Keywords: N-heterocyclic carbene; olefin metathesis; percent buried volume; ruthenium–indenylidene; Tolman electronic parameter; Introduction The use of N-heterocyclic carbenes (NHC) as spectator ligands in ruthenium-mediated olefin metathesis represents one of the most important breakthroughs

• system, since it is easily synthesised and handled [34]. In this work, a series of [RhCl(CO)2(NHC)] complexes were synthesized in order to evaluate the electronic donor ability of the NHCs. The free carbenes were prepared according to literature procedures. Free IMes (4b) [35] and IMesMe (4a) [36] were

Light-induced olefin metathesis

• Yuval Vidavsky and
• N. Gabriel Lemcoff

Beilstein J. Org. Chem. 2010, 6, 1106–1119, doi:10.3762/bjoc.6.127

• phenylacetylene. These works were based on earlier observations by Katz et al. [56][57] and Geoffrey et al. [58] that acetylenes irradiated in the presence of tungsten complexes form metal carbenes that can produce polymeric species. Well-defined tungsten catalysed photometathesis The first example of well

Halide exchanged Hoveyda-type complexes in olefin metathesis

• Julia Wappel,
• César A. Urbina-Blanco,
• Mudassar Abbas,
• Jörg H. Albering,
• Robert Saf,
• Steven P. Nolan and
• Christian Slugovc

Beilstein J. Org. Chem. 2010, 6, 1091–1098, doi:10.3762/bjoc.6.125

• -heterocyclic carbenes (NHC) as co-ligands in ruthenium-based carbene complexes for olefin metathesis [1][2][3] in the late nineties of the last century, olefin metathesis has become a powerful carbon-carbon double-bond-forming tool presenting unique synthetic opportunities [4]. Developments in this area can be

Intramolecular hydroxycarbene C–H-insertion: The curious case of (o-methoxyphenyl)hydroxycarbene

• Dennis Gerbig,
• David Ley,
• Hans Peter Reisenauer and
• Peter R. Schreiner

Beilstein J. Org. Chem. 2010, 6, 1061–1069, doi:10.3762/bjoc.6.121

• ][19][20] (Scheme 2). (o-Methoxyphenyl)hydroxycarbene (5) serves as the model compound for studying the intramolecular carbene C–H-bond insertion both under matrix isolation and solution conditions (Scheme 3). The generation of such carbenes in solution in high-boiling solvents would also provide

• performed, containing radii based on the United Atom Topological Model as implemented in Gaussian09. Tunneling half-lives τ1/2 of carbenes 5 and 12 were estimated employing a) a simple Eckart barrier methodology [36][37], and b) the one-dimensional Wentzel–Kramers–Brillouin approximation [13][14][37][38

• that undergoes insertion. Acid-catalyzed generation of 7 by unreacted 6. Computed half-lives (unscaled) for the [1,2]H-tunneling reaction in carbenes 3, 5, and 12 at 11 K. The measured half-life of 3 is 2.5 h at 11 K. The thermal barrier for the [1,2]H-shift was computed at AE-CCSD(T)/cc-pVDZ // M06-2X

CAAC Boranes. Synthesis and characterization of cyclic (alkyl) (amino) carbene borane complexes from BF₃ and BH₃

• Julien Monot,
• Louis Fensterbank,
• Max Malacria,
• Emmanuel Lacôte,
• Steven J. Geib and
• Dennis P. Curran

Beilstein J. Org. Chem. 2010, 6, 709–712, doi:10.3762/bjoc.6.82

• 10.3762/bjoc.6.82 Abstract In situ formation of two cyclic (alkyl) (amino) carbenes (CAACs) followed by addition of BF3•Et2O provided the first two examples of CAAC–BF3 complexes: 1-(2,6-diisopropylphenyl)-3,5,5-trimethyl-3-phenylpyrrolidin-2-ylidene trifluoroborane, and 2-(2,6-diisopropylphenyl)-3,3

• formed in situ according to 1H and 11B NMR analysis, but did not survive the workup conditions. These results set the stage for further studies of the chemistry of CAAC boranes. Keywords: borane Lewis acid Lewis base complexes; carbene–borane complexes; cyclic (alkyl) (amino) carbenes; N-heterocyclic

• carbenes; stable carbenes; Introduction Lewis acid/Lewis base complexes of N-heterocyclic carbenes and boranes (NHC–boranes) are readily prepared from NHC’s and boranes by direct complexation [1][2][3][4]. Unlike many other classes of Lewis base complexes of boranes with neutral molecules (ethers

Synthesis and crossover reaction of TEMPO containing block copolymer via ROMP

• Olubummo Adekunle,
• Susanne Tanner and
• Wolfgang H. Binder

Beilstein J. Org. Chem. 2010, 6, No. 59, doi:10.3762/bjoc.6.59

• lower polydispersities of the resulting polymers. Recently, structural variations of G1–G3 catalysts generated a new series of catalysts U1–U3 bearing indenyl-carbenes instead of benzylidene-carbenes. These new catalysts are now commercially available and are well known as the Umicore catalysts (NEOLYST

Expedient syntheses of the N-heterocyclic carbene precursor imidazolium salts IPr·HCl, IMes·HCl and IXy·HCl

• Lukas Hintermann

Beilstein J. Org. Chem. 2007, 3, No. 22, doi:10.1186/1860-5397-3-22

• involving a 1,5-dipolar electrocyclization is proposed. Background Imidazolylidene carbenes have been investigated as ligands in coordination chemistry, as powerful steering/controlling elements in transition-metal catalysis,[1][2] and more recently as metal-free catalysts for organic reactions[3][4]. Some

• prominent members of the family of N-heterocyclic carbenes (NHC) are the sterically encumbered imidazolylidenes IPr and IMes (Figure 1), which can also be considered as analogues of bulky and electron-rich tertiary phosphanes. In contrast to the latter, their synthesis does not involve air-sensitive or

• full experimental data. The carbenes IPr, IMes, IXy and their imidazolium salt precursors Synthetic routes to and diazadiene precursors for imidazolium salts. The imidazolium salt synthesis as a 1, 5-dipolar electrocyclization. Potential side-reactions in the imidazolium salt synthesis. Optimization of

Trapping evidence for the thermal cyclization of di-(o-acetylphenyl)acetylene to 3,3'-dimethyl- 1,1'-biisobenzofuran

• Charles P. Casey,
• Neil A. Strotman and
• Ilia A. Guzei

Beilstein J. Org. Chem. 2005, 1, No. 18, doi:10.1186/1860-5397-1-18

• electrocyclic ring closures to furans.[9][17][18] Related ring closures of o-acyl phenylcarbenes to isobenzofurans have been reported (Scheme 9).[19][20][21] These carbenes were formed as transient intermediates by photolytic or chemical cleavage of diazo or diazirine compounds. Isobenzofurans formed in this