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

• the photogenically-produced iminium ion 27a, thus achieving the formation of Csp3–Csp bonds. Rovis and coworkers recently developed another mode of dual catalysis involving visible light photocatalysis with chiral N-heterocyclic carbene catalysis, which allows catalytic asymmetric α-acylation of N

• -aryltetrahydroisoquinoline 13 with an aliphatic aldehyde (Scheme 11) [78]. In the presence of a N-heterocyclic carbene (NHC), the aldehyde is converted to a chiral acyl anion or homoenolate equivalent 37, which is then added to the iminium ion 27 to form Csp3–Csp2 bonds asymmetrically. It is interesting to note that the use

• synthetic transformations to produce a diverse array of amines. Moreover, visible light photoredox catalysis has been merged with other types of catalysis, including enamine catalysis, N-heterocyclic carbene (NHC) catalysis, or copper acetylide formation. This dual catalysis approach has significantly

True and masked three-coordinate T-shaped platinum(II) intermediates

• Manuel A. Ortuño,
• Salvador Conejero and
• Agustí Lledós

Beilstein J. Org. Chem. 2013, 9, 1352–1382, doi:10.3762/bjoc.9.153

• -heterocyclic carbene (NHC) ligands (Figure 6), which have been proven to be useful stabilizing electron-deficient transition-metal species [25][26][27]. In this regard, recent studies state that the use of IMes* (4,5-dimethyl-1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and IMes (1,3-bis(2,4,6

• lack of agostic interactions in these complexes. This absence has been attributed to the strong trans influence exerted by the ligand in trans position with respect to the vacant site [23][24]. Moreover, in the past few years the synthesis of 14-electron Pt(II) complexes was extended by using N

Synthesis and structure of trans-bis(1,4-dimesityl-3-methyl-1,2,3-triazol-5-ylidene)palladium(II) dichloride and diacetate. Suzuki–Miyaura coupling of polybromoarenes with high catalytic turnover efficiencies

• Jeelani Basha Shaik,
• Venkatachalam Ramkumar,
• Babu Varghese and
• Sethuraman Sankararaman

Beilstein J. Org. Chem. 2013, 9, 698–704, doi:10.3762/bjoc.9.79

• structures of the chloro (1) as well as the corresponding acetato (2) complexes are also reported and compared with the corresponding complexes of 1,4-diphenyl-3-methyl-1,2,3-triazol-5-ylidene as the ligand. Keywords: C–C coupling; N-heterocyclic carbene; palladium; Suzuki–Miyaura coupling; 1,2,3

Reductions of aldehydes and ketones with a readily available N-heterocyclic carbene borane and acetic acid

• Vladimir Lamm,
• Xiangcheng Pan,
• Tsuyoshi Taniguchi and
• Dennis P. Curran

Beilstein J. Org. Chem. 2013, 9, 675–680, doi:10.3762/bjoc.9.76

• Vladimir Lamm Xiangcheng Pan Tsuyoshi Taniguchi Dennis P. Curran Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260 USA 10.3762/bjoc.9.76 Abstract Acetic acid promotes the reduction of aldehydes and ketones by the readily available N-heterocyclic carbene borane, 1,3

• scale, products are isolated by evaporation of the reaction mixture and direct chromatography. Keywords: NHC-borane; N-heterocyclic carbene borane; reduction; Introduction Reduction of carbonyl compounds is a common, fundamental chemical transformation. Among the numerous hydride reagents available

• decomposition with the release of hydrogen gas. Therefore, appropriate precautions are required for larger scale reactions as well as during transport and storage [5]. N-Heterocyclic carbene boranes (NHC-boranes) have emerged in recent years as a useful class of synthetic reagents, which have interesting

1-n-Butyl-3-methylimidazolium-2-carboxylate: a versatile precatalyst for the ring-opening polymerization of ε-caprolactone and rac-lactide under solvent-free conditions

• Astrid Hoppe,
• Faten Sadaka,
• Claire-Hélène Brachais,
• Gilles Boni,
• Jean-Pierre Couvercelle and
• Laurent Plasseraud

Beilstein J. Org. Chem. 2013, 9, 647–654, doi:10.3762/bjoc.9.73

• pentaerythritol as initiator alcohols, and the products were fully characterized by 1H and 13C{1H} NMR spectroscopy, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). BMIM-2-CO2 acts as an N-heterocyclic carbene precursor, resulting from in situ decarboxylation, either by heating

• decrease from 50% (benzyl alcohol, 1) through 44% (glycerol, 2) to 35% (pentaerythritol, 4). From a mechanistic point of view, the formation of the target polymers can be postulated by the in situ decarboxylation of BMIM-2-CO2, which generates free N-heterocyclic carbene species. In the absence of BMIM-2

• induced either in vacuo (method A) or by the addition of NaBPh4 (method B). On the basis of previous studies reported by Waymouth and Hedrick [34], we suggest that the in situ generated N-heterocyclic carbene acts as a nucleophilic species and leads to the opening of cyclic esters (initiation step, Scheme

NHC-catalysed highly selective aerobic oxidation of nonactivated aldehydes

• Lennart Möhlmann,
• Stefan Ludwig and
• Siegfried Blechert

Beilstein J. Org. Chem. 2013, 9, 602–607, doi:10.3762/bjoc.9.65

• -free oxidation; N-heterocyclic carbene; organocatalysis; Introduction The development of efficient and selective aerobic oxidation methods for organic substrates is of increasing interest and an attractive goal in green chemistry [1][2][3]. In a recent communication we reported on selective oxidation

• of carbinols to aldehydes or ketones using oxygen, visible light and mesoporous graphitic carbon nitride (mpg-C3N4) polymer as a metal-free photocatalyst [4]. As an extension of this method we were interested in a consecutive organocatalytic process using an N-heterocyclic carbene (NHC) together with

N-Heterocyclic carbene–palladium catalysts for the direct arylation of pyrrole derivatives with aryl chlorides

• Ismail Özdemir,
• Nevin Gürbüz,
• Nazan Kaloğlu,
• Öznur Doğan,
• Murat Kaloğlu,
• Christian Bruneau and
• Henri Doucet

Beilstein J. Org. Chem. 2013, 9, 303–312, doi:10.3762/bjoc.9.35

• ligands, which are electronically and sterically tunable, and which generally form thermally stable compounds with different metal ions, are strong σ-donors. These qualities have rendered N-heterocyclic carbene ligands as classical substitutes to phosphines in organometallic catalysis [10][11][12][13][14

• the palladium-catalyzed coupling of heteroarenes with aryl halides through a C–H bond activation has been largely explored. On the other hand, the influence of carbene ligands for such couplings remains largely unexplored [40][41][42][43][44][45][46][47]. Quite congested N-heterocyclic carbene

• carbene ligand, was reported by Lee and co-workers for the direct arylation of imidazoles with some aryl chlorides [46]. However, to our knowledge, N-heterocyclic carbene ligands have not yet been employed for the palladium-catalyzed direct arylation of pyrroles with aryl chlorides. As carbene ligands

Recent advances in transition-metal-catalyzed intermolecular carbomagnesiation and carbozincation

• Kei Murakami and
• Hideki Yorimitsu

Beilstein J. Org. Chem. 2013, 9, 278–302, doi:10.3762/bjoc.9.34

• ). Recently, iron and cobalt have been regarded as efficient catalysts for carbometalation of simple alkynes. Shirakawa and Hayashi reported that iron salts could catalyze arylmagnesiation of arylacetylenes in the presence of an N-heterocyclic carbene (NHC) ligand (Scheme 29) [103]. In 2012, Shirakawa and

Alkyne hydroarylation with Au N-heterocyclic carbene catalysts

• Cristina Tubaro,
• Marco Baron,
• Andrea Biffis and
• Marino Basato

Beilstein J. Org. Chem. 2013, 9, 246–253, doi:10.3762/bjoc.9.29

• Cristina Tubaro Marco Baron Andrea Biffis Marino Basato Dipartimento di Scienze Chimiche, Università degli Studi di Padova, via Marzolo 1, 35131 Padova, Italy 10.3762/bjoc.9.29 Abstract Mono- and dinuclear gold complexes with N-heterocyclic carbene (NHC) ligands have been employed as catalysts in

• (II) salts as catalyst [8][9][10]. Palladium complexes with N-heterocyclic carbene (NHC) ligands have since been showcased as highly efficient catalysts for this reaction [11][12][13][14]. Alternative catalytic systems based on salts or complexes of other noble metals, such as platinum [15][16][17

N-Heterocyclic carbene–palladium(II)-1-methylimidazole complex catalyzed Mizoroki–Heck reaction of aryl chlorides with styrenes

• Ting-Ting Gao,
• Ai-Ping Jin and
• Li-Xiong Shao

Beilstein J. Org. Chem. 2012, 8, 1916–1919, doi:10.3762/bjoc.8.222

• Ting-Ting Gao Ai-Ping Jin Li-Xiong Shao College of Chemistry and Materials Engineering, Wenzhou University, Chashan University Town, Zhejiang Province 325035, People’s Republic of China 10.3762/bjoc.8.222 Abstract A well-defined N-heterocyclic carbene–palladium(II)-1-methylimidazole [NHC-Pd(II

• ) as the ionic liquid. Keywords: aryl chloride; Mizoroki–Heck reaction; N-heterocyclic carbene; palladium complex; synthetic method; Introduction The palladium-catalyzed reaction between organic halides and alkenes, the Mizoroki–Heck reaction, is one of the most versatile methods for the formation of

• broad substrate scope, is still a current topic of interest. Recently, we have demonstrated that the well-defined N-heterocyclic carbene–palladium(II)-1-methylimidazole [NHC-Pd(II)-Im] complex 1 (Figure 1), which can be easily prepared from commercially available PdCl2, IPr.HCl [1,3-bis(2,6

Extending the utility of [Pd(NHC)(cinnamyl)Cl] precatalysts: Direct arylation of heterocycles

• Anthony R. Martin,
• Anthony Chartoire,
• Alexandra M. Z. Slawin and
• Steven P. Nolan

Beilstein J. Org. Chem. 2012, 8, 1637–1643, doi:10.3762/bjoc.8.187

• efficiency of well-defined palladium catalysts bearing NHC (N-heterocyclic carbene) ancillary ligands in classical cross-coupling reactions, they have rarely been applied to direct arylation procedures [9][10][11][12][13][14][15][16]. Among the family of [Pd(NHC)] complexes, the [Pd(NHC)(cin)Cl] (cin

C2-Alkylation of N-pyrimidylindole with vinylsilane via cobalt-catalyzed C–H bond activation

• Zhenhua Ding and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2012, 8, 1536–1542, doi:10.3762/bjoc.8.174

• pyphos, which was the optimum ligand for the alkenylation reaction [33], was poorly effective (Table 1, entry 6). Additional screening of N-heterocyclic carbene (NHC) and phosphine ligands did not lead to an improvement of the catalytic efficiency (Table 1, entries 7–9). The reaction turned out to be

N-Heterocyclic carbene-catalyzed direct cross-aza-benzoin reaction: Efficient synthesis of α-amino-β-keto esters

• Takuya Uno,
• Yusuke Kobayashi and
• Yoshiji Takemoto

Beilstein J. Org. Chem. 2012, 8, 1499–1504, doi:10.3762/bjoc.8.169

• with α-imino ester, catalyzed by N-heterocyclic carbene, leads chemoselectively to α-amino-β-keto esters in moderate to good yields with high atom efficiency. The reaction mechanism is discussed, and it is proposed that the α-amino-β-keto esters are formed under thermodynamic control. Keywords: α

A quantitative approach to nucleophilic organocatalysis

• Herbert Mayr,
• Sami Lakhdar,
• Biplab Maji and
• Armin R. Ofial

Beilstein J. Org. Chem. 2012, 8, 1458–1478, doi:10.3762/bjoc.8.166

• ]. Quantitative aspects of N-heterocyclic carbene (NHC) catalysis As the following discussion will focus on the difference between the kinetic term “nucleophilicity” and the thermodynamic term “Lewis basicity”, let us first illustrate this aspect by comparing the behavior of two well-known organocatalysts, 1,4

N-Heterocyclic carbene/Brønsted acid cooperative catalysis as a powerful tool in organic synthesis

• Rob De Vreese and
• Matthias D’hooghe

Beilstein J. Org. Chem. 2012, 8, 398–402, doi:10.3762/bjoc.8.43

• functionalized pyrrolidin-2-ones as valuable scaffolds in heterocyclic chemistry. This Commentary will briefly highlight the concept of N-heterocyclic carbene/Brønsted acid cooperative catalysis as a new and powerful methodology in organic chemistry. Keywords: Brønsted acids; cooperative catalysis; γ-lactams; N

• preparation and characterization of a metal carbene complex in 1964 through nucleophilic attack of phenyllithium at tungsten hexacarbonyl followed by O-alkylation [1], and Arduengo described the preparation of the first free and stable N-heterocyclic carbene 2 by deprotonation of the corresponding imidazolium

• with chiral (amino) acids could deliver functionalized γ-lactams with high enantioselectivity as well. Conclusion In summary, the use of the N-heterocyclic carbene/Brønsted acid system should be considered as a novel aspect of cooperative catalysis, providing new opportunities for research in this area

Synthetic approaches to multifunctional indenes

• Neus Mesquida,
• Sara López-Pérez,
• Immaculada Dinarès and
• Ermitas Alcalde

Beilstein J. Org. Chem. 2011, 7, 1739–1744, doi:10.3762/bjoc.7.204

• ; amides; indanones; indenes; organometallic reagents; Introduction Compounds with an indene core are of great interest as precursors of metallocene complexes for catalytic polymerization processes, as well as being present in N-heterocyclic carbene ligands and functional materials [1][2][3][4][5][6][7][8

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

• Pd-catalyzed cross-coupling approach starting from 1-chloro-2-iodobenzenes, phenylacetylene and a variety of primary amines [28][29]. The sequential three-component reaction was performed with the aid of an N-heterocyclic carbene-palladium complex generated in situ, derived from imidazolium salt 50

Combination of gold catalysis and Selectfluor for the synthesis of fluorinated nitrogen heterocycles

• Antoine Simonneau,
• Pierre Garcia,
• Jean-Philippe Goddard,
• Virginie Mouriès-Mansuy,
• Max Malacria and
• Louis Fensterbank

Beilstein J. Org. Chem. 2011, 7, 1379–1386, doi:10.3762/bjoc.7.162

• hydrofluorination of alkynes catalyzed by N-heterocyclic carbene gold(I) complexes [4], or by fluorodeauration of transient vinyl gold species [5][6], has been previously reported in the literature. On the basis of our recent results on the gold-catalyzed cyclization of enynes [7][8][9][10] and allenylhydrazones

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

• Michel Chiarucci Mirko Locritani Gianpiero Cera Marco Bandini Dipartimento di Chimica “G. Ciamician”, Alma Mater Studiorum – Università di Bologna, Via Selmi 2, 40126 Bologna, Italy 10.3762/bjoc.7.139 Abstract Gold(I)-N-heterocyclic carbene (NHC) complexes proved to be a reliable catalytic system

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

• regenerating the catalyst (PtCl2). In addition, DFT calculations suggested that gold catalysts could be even more active than PtCl2. Accordingly, the use of a cationic Au(I) catalyst containing a σ-donating N-heterocyclic carbene ligand (Au6/AgSbF6, Scheme 26) enabled these reactions at lower temperatures and

Triazole–Au(I) complex as chemoselective catalyst in promoting propargyl ester rearrangements

• Dawei Wang,
• Yanwei Zhang,
• Rong Cai and
• Xiaodong Shi

Beilstein J. Org. Chem. 2011, 7, 1014–1020, doi:10.3762/bjoc.7.115

• (I) catalysis. The recent development of N-heterocyclic carbene (NHC) derivatives has significantly expanded the choice of ligands by improving the catalyst stability through metal-ligand backbonding [17][18][19][20]. To access the active catalyst [L–Au]+, stable precursors L–Au–X or [L–Au–X]+·A

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

• % PPh3AuCl/5 mol % AgOTf in dichloroethane at 80 °C gave alkylidenecyclobutanamine 160 in 65% yield as a single olefin isomer (Scheme 28). The formation of tri- and tetrasubstituted pyrroles 163 [74] via cationic N-heterocyclic carbene–gold(I) complex catalyzed amino Claisen rearrangement of N-propargyl-β

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

• functionalisation of aromatic C–H bonds. Doubt is cast on the commonly cited route of halide abstraction from gold and evidence of substrate activation is given. Keywords: C–H functionalisation; gold catalyst; halide abstraction; N-heterocyclic carbene; silver salt; substrate activation; Introduction The use of

Solvent- and ligand-induced switch of selectivity in gold(I)-catalyzed tandem reactions of 3-propargylindoles

• Estela Álvarez,
• Delia Miguel,
• Patricia García-García,
• Manuel A. Fernández-Rodríguez,
• Félix Rodríguez and
• Roberto Sanz

Beilstein J. Org. Chem. 2011, 7, 786–793, doi:10.3762/bjoc.7.89

• N-heterocyclic carbene ligands [30] also produced 3a as the major compound of the corresponding mixtures (Table 1, entries 5 and 6). It was decided to increase the π-acceptor character of the ligand [31], and, in this case, the employment of a triphenylphosphite–gold(I) complex led to a slight

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

• moderate results, whereas the highest yield and diastereoselectivity was obtained when the strong σ donor and weak π acceptor N-heterocyclic carbene IPr was the ligand. The latter was indeed anticipated to give an organogold with a higher carbene-like reactivity which favors olefin cyclopropanation. AuCl