The activity of indenylidene derivatives in olefin metathesis catalysts

• Maria Voccia,
• Steven P. Nolan,
• Luigi Cavallo and
• Albert Poater

Beilstein J. Org. Chem. 2018, 14, 2956–2963, doi:10.3762/bjoc.14.275

• ] developed well-defined homogeneous catalysts that the area truly blossomed. Using a metal carbene complex as a catalyst, making use of the Chauvin mechanism, olefin metathesis consists of the redistribution of two carbon–carbon double bonds [9]. The metal and its ligand environment in both ruthenium and

• the existing commercial catalysts, playing mainly with the electronic characteristics of the ligands (usually two chlorides and an ylidene ligand) [15][16][17], whereas basically the sterics of the substituents on the N-heterocyclic carbene (NHC) ligand have remained unchanged [18]. Overall, any

The influence of the cationic carbenes on the initiation kinetics of ruthenium-based metathesis catalysts; a DFT study

• Magdalena Jawiczuk,
• Angelika Janaszkiewicz and
• Bartosz Trzaskowski

Beilstein J. Org. Chem. 2018, 14, 2872–2880, doi:10.3762/bjoc.14.266

• different distances from the carbene carbon. We show that the predicted initiation rates of Grubbs, indenylidene, and Hoveyda–Grubbs-like complexes incorporating these carbenes show little variance and are similar to initiation rates of standard Grubbs, indenylidene, and Hoveyda–Grubbs catalysts. In all

• investigated cases the partial charge of the carbene carbon atom is similar, resulting in comparable Ccarbene–Ru bond strengths and Ru–P/O dissociation Gibbs free energies. Keywords: catalysts; cationic carbenes; DFT; initiation; metathesis; Introduction The isolation of the first stable N-heterocyclic

• carbene (NHC) by Arduengo [1] was a milestone in organic chemistry which allowed for thorough and systematic studies on all aspects of NHC chemistry in the past 25 years [2][3][4][5][6][7]. It was soon realized that NHCs are a very useful class of ligands for transition metal catalysis as both their

Olefin metathesis catalysts embedded in β-barrel proteins: creating artificial metalloproteins for olefin metathesis

• Daniel F. Sauer,
• Johannes Schiffels,
• Takashi Hayashi,
• Ulrich Schwaneberg and
• Jun Okuda

Beilstein J. Org. Chem. 2018, 14, 2861–2871, doi:10.3762/bjoc.14.265

• modification of the first coordination sphere by adding an N-heterocyclic carbene (NHC) ligand and a chelating styrene to the so-called Grubbs 1st generation catalyst, the relatively air- and moisture-stable Grubbs–Hoveyda type (GH-type) catalysts were obtained [7]. These catalysts do not only show stability

Domino ring-opening–ring-closing enyne metathesis vs enyne metathesis of norbornene derivatives with alkynyl side chains. Construction of condensed polycarbocycles

• Ritabrata Datta and
• Subrata Ghosh

Beilstein J. Org. Chem. 2018, 14, 2708–2714, doi:10.3762/bjoc.14.248

• diene. Thus unlike metathesis of 7a, metathesis of its acetate analogue 7b occurred through a domino ROM–RCEYM process. Addition of the Ru-carbene 10 arising from ring opening of norbornene unit in 7b could add to the acetylenic unit of another molecule of 7b leading to copolymerization. However, this

• process generally does not take place under such low molar concentration of the substrate [38][39][40][41][42][43]. We also did not isolate any copolymerization product. This may be attributed to the much faster rate of addition of the Ru-carbene 10 to the yne unit intramolecularly resulting in ring

Ring-opening metathesis of some strained bicyclic systems; stereocontrolled access to diolefinated saturated heterocycles with multiple stereogenic centers

• Zsanett Benke,
• Melinda Nonn,
• Márton Kardos,
• Santos Fustero and
• Loránd Kiss

Beilstein J. Org. Chem. 2018, 14, 2698–2707, doi:10.3762/bjoc.14.247

• carbene-based catalysts (G-2 and HG-2) were effective in case of bridged lactones with a six-membered ring part in their framework, with O-functionalities (±)-3, (±)-4, (±)-9 and (±)-14. In case of isoxazoline-fused derivative (±)-16 G-1 gave the best result, while in case of lactam (±)-18 HG-1 was the

Synthesis of cis-hydrindan-2,4-diones bearing an all-carbon quaternary center by a Danheiser annulation

• Gisela V. Saborit,
• Carlos Cativiela,
• Ana I. Jiménez,
• Josep Bonjoch and
• Ben Bradshaw

Beilstein J. Org. Chem. 2018, 14, 2597–2601, doi:10.3762/bjoc.14.237

• takes place from polyfunctionalized cyclohexanones or related compounds through a Michael reaction [7], successive inter- and intramolecular radical processes [8], intramolecular carbene addition/cyclization [9][10], aldol cyclizations either under Lewis acid catalysis [11] or from diazoketones in the

Carbonylonium ions: the onium ions of the carbonyl group

• Daniel Blanco-Ania and
• Floris P. J. T. Rutjes

Beilstein J. Org. Chem. 2018, 14, 2568–2571, doi:10.3762/bjoc.14.233

• . Applying systematic nomenclature to intermediates 1 would generate the cumbersome names “organylidene oxonium ions” or “organylidene oxidanium ions” [34]. Clearly, the length and complexity of these names would prevent researchers from using them. Another alternative would be to combine the terms “carbene

Diazirine-functionalized mannosides for photoaffinity labeling: trouble with FimH

• Femke Beiroth,
• Tomas Koudelka,
• Thorsten Overath,
• Stefan D. Knight,
• Andreas Tholey and
• Thisbe K. Lindhorst

Beilstein J. Org. Chem. 2018, 14, 1890–1900, doi:10.3762/bjoc.14.163

• these requirements particularly well. The diazirine photophore is small and its photoactivation is possible at wavelengths around 350 nm and thus does not perturb protein structures. According to the literature, irradiation of a diazirine-functionalized ligand leads to a reactive carbene which can

• diazirine 3, with scoring values of −34.7 (open gate) and −36.2 (closed gate), is predicted as suitable FimH ligand with high affinity. Additionally, docking suggests that the diazirine function of 3 is positioned in close proximity to the protein surface, making a specific insertion reaction of the carbene

• with mannoside 4 were less promising and are not reported here. After all, also modeling had suggested that 3 has a higher affinity for FimH than 4. To test carbene formation, mannoside 3 was irradiated at 345 nm in 1:1 acetonitrile/water as well as in 1:1 DMSO/water mixtures with 4-hydroxybenzyl

Water-soluble SNS cationic palladium(II) complexes and their Suzuki–Miyaura cross-coupling reactions in aqueous medium

• Alphonse Fiebor,
• Richard Tia,
• Banothile C. E. Makhubela and
• Henok H. Kinfe

Beilstein J. Org. Chem. 2018, 14, 1859–1870, doi:10.3762/bjoc.14.160

• catalyst for subsequent reactions after simple phase separation [31]. However, the commonly employed phosphorous and carbene ligand-based palladium(II) complexes are found to be in most cases sensitive to moisture and air limiting the scope of their catalytic application in aqueous reactions [32][33]. This

Visible light-mediated difluoroalkylation of electron-deficient alkenes

• Vyacheslav I. Supranovich,
• Vitalij V. Levin,
• Marina I. Struchkova,
• Jinbo Hu and
• Alexander D. Dilman

Beilstein J. Org. Chem. 2018, 14, 1637–1641, doi:10.3762/bjoc.14.139

• carbene/borane complex and 400 nm light [48]. Results and Discussion Iodide 1a was selected as a model substrate and its reaction with tert-butyl acrylate (2a) was evaluated in the presence of various boron hydrides (Table 1). The reaction was performed in methanol with irradiation by a strip of blue

Hypervalent organoiodine compounds: from reagents to valuable building blocks in synthesis

• Gwendal Grelier,
• Benjamin Darses and
• Philippe Dauban

Beilstein J. Org. Chem. 2018, 14, 1508–1528, doi:10.3762/bjoc.14.128

• involve the formation of the copper-carbene species 35, to which the carboxylate of alkynylbenziodoxolone could add to afford the intermediate 36. Final alkynyl transfer would give rise to the products 31 and 33, however, the nature of this alkynylation step remains to be elucidated. In a subsequent study

Recent advances in phosphorescent platinum complexes for organic light-emitting diodes

• Cristina Cebrián and
• Matteo Mauro

Beilstein J. Org. Chem. 2018, 14, 1459–1481, doi:10.3762/bjoc.14.124

• ][30]. Apart from the strong σ-donor ability, the great interest for these ligands relies on the robustness that they confer to the resulting complexes, upon coordination onto both early [31] and late transition metals [32][33]. In this regard, the group of Chi employed carbene-based chelates as

• neutral imine substitutes in an attempt to further improved the stability and the performances of their N···H–C stabilized phosphors (Figure 5) [34][35]. Either when one, compound 10 [34], or two, compound 11 [35], carbene moieties were used, the resulting platinum compounds were basically nonemissive in

• −1 for 11a, and EQE = 11.2%, CE = 40.6 cd A−1 and PE = 25.8 lm W−1 for 11b. In consequence, the use of only one carbene moiety seemed to afford very appealing photophysical features both for display and lighting applications. The beneficial effect of carbene moieties on the photophysical features of

Atom-economical group-transfer reactions with hypervalent iodine compounds

• Andreas Boelke,
• Peter Finkbeiner and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2018, 14, 1263–1280, doi:10.3762/bjoc.14.108

• -catalysed reaction with diazo compounds 42 (Scheme 22) [56]. This strategy is not only atom economic regarding the applied hypervalent iodine reagent but also with regard to the chosen substrate. The metal carbene species generated from the diazo compounds displays nucleophilic as well as electrophilic

A survey of chiral hypervalent iodine reagents in asymmetric synthesis

• Soumen Ghosh,
• Suman Pradhan and
• Indranil Chatterjee

Beilstein J. Org. Chem. 2018, 14, 1244–1262, doi:10.3762/bjoc.14.107

• the enolate intermediate 111 followed by the generation of a C–C bond via conjugate addition delivered intermediate carbene 113. A 1,2-hydrogen shift led to the formation of products 108 with enantioselectivities up to 79% (Scheme 24). Later, Maruoka et al. improved the enantioselectivity up to 95% ee

• 115 and 119, respectively, with decent enantioselectivity (Scheme 25) [77]. The formation of an alkylidene carbene 117 and its rapid rearrangement via 1,2-silyl shift (in case of R = silyl group) into the alkylated β-ketoesters 115 can fairly explain the reaction outcome. On the other hand, the ligand

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

• (Scheme 8). After bromination of 40 with molecular bromine in carbon tetrachloride, direct dehydrobromination with lithium chloride in dimethylformamide gave 11 in 85% isolated yield. Müller’s group reported an alternative synthesis for 11 starting from the carbene adduct 41 over two or three steps [55

• sodium salt of 4,5-benzotropone (11) and defined carbene–carbene rearrangements of 77–79 before finally it was verified by trapping of unstable intermediates 77–79 (Scheme 14) [77]. In 2002, McMahon reported obtaining the naphthylcarbene rearrangement manifold via the carbonyl groups of the isomeric

• -triene (78), and triplet 2-naphthylcarbene (79). Formation of allene 83 as an alternative carbene rearrangement product was not detected under the studied photolysis conditions (Scheme 14). Kitahara’s group reported the one-step synthesis of heptafulvalenes and benzoheptafulvalenes from monocyclic

Electrochemically modified Corey–Fuchs reaction for the synthesis of arylalkynes. The case of 2-(2,2-dibromovinyl)naphthalene

• Fabiana Pandolfi,
• Isabella Chiarotto and
• Marta Feroci

Beilstein J. Org. Chem. 2018, 14, 891–899, doi:10.3762/bjoc.14.76

• ) increases the yield of 5a and substitutes 1a (as proton donor) in reaction 2 (Scheme 6). The anion generated by cathodic reduction of dibromoalkene 1a (Scheme 2, reaction 1) can also eliminate bromide (as reported in literature [31]), yielding the corresponding carbene (Scheme 2, reaction 2). This carbene

Cobalt-catalyzed directed C–H alkenylation of pivalophenone N–H imine with alkenyl phosphates

• Wengang Xu and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2018, 14, 709–715, doi:10.3762/bjoc.14.60

• Wengang Xu Naohiko Yoshikai Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore 10.3762/bjoc.14.60 Abstract A cobalt–N-heterocyclic carbene (NHC) catalyst efficiently promotes an ortho C–H

• demonstrated that the combination of a cobalt–N-heterocyclic carbene (NHC) catalyst and a Grignard reagent allows for the arene C–H functionalization with organic halides and pseudohalides under the assistance of nitrogen directing groups [17][22][23][24][25][26][27]. In this connection, Ackermann developed a

Enhanced quantum yields by sterically demanding aryl-substituted β-diketonate ancillary ligands

• Rebecca Pittkowski and
• Thomas Strassner

Beilstein J. Org. Chem. 2018, 14, 664–671, doi:10.3762/bjoc.14.54

• calculations. Experimental Both complexes were characterized by 1H, 13C, and 195Pt NMR spectroscopy, ESIMS, and elemental analysis. Formation of the carbene complexes was verified by the disappearance of the characteristic NCHN proton signal of the imidazolium salt in the 1H NMR experiment. The syntheses of

One-pot sequential synthesis of tetrasubstituted thiophenes via sulfur ylide-like intermediates

• Jun Ki Kim,
• Hwan Jung Lim,
• Kyung Chae Jeong and
• Seong Jun Park

Beilstein J. Org. Chem. 2018, 14, 243–252, doi:10.3762/bjoc.14.16

• ], these carbene precursors have been played an important role in organic chemistry [10][11][12][13][14][15][16][17][18][19][20][21][22]. As shown in Figure 1, sulfur(IV) and sulfur(VI) ylides are stable. The stability of sulfonium ylides is determined by the electron delocalization of the carbanionic

• . Based on previous reports regarding carbene generation from sulfonium ylides [6][85][86], compounds 9a and 9b were reacted with excess MeOH (Scheme 2). Interestingly, 2-pyridyl-substituted N,S-acetal 9b only provided N,O-acetal 9ba via a 1,4-Micheal addition, whereas N,S-acetal 9a was completely

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation. Part 1: Use of CF₃SO₂Na

• Hélène Guyon,
• Hélène Chachignon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2764–2799, doi:10.3762/bjoc.13.272

Comparative profiling of well-defined copper reagents and precursors for the trifluoromethylation of aryl iodides

• Peter T. Kaplan,
• Jessica A. Lloyd,
• Mason T. Chin and
• David A. Vicic

Beilstein J. Org. Chem. 2017, 13, 2297–2303, doi:10.3762/bjoc.13.225

• facilitate meaningful comparative studies, such as structural and electrochemical ones [2]. N-Heterocyclic carbene (NHC) complexes of copper such as A1 (Scheme 1) were the first well-defined and structurally characterized copper–CF3 complexes that display activity for the trifluoromethylation of aryl halides

Dialkyl dicyanofumarates and dicyanomaleates as versatile building blocks for synthetic organic chemistry and mechanistic studies

• Grzegorz Mlostoń and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 2235–2251, doi:10.3762/bjoc.13.221

• corresponding E-1 [10] (Scheme 2). Alternatively, the same transformation can be performed with 3 and thiourea derivative 4 in a two-step reaction through intermediate 5 [11] (Scheme 2). The latter, upon treatment with Et3N, generates a carbene [:C(CN)CO2Et], which dimerizes to give E-1a albeit in low yield

• . The dimerization of the same carbene leading to a mixture of E- and Z-1a was observed when ethyl dibromocyanoacetate was treated with equimolar amounts of LiI in DMF at room temperature with the highest reported yield of 83% [12]. The dimethyl ester E-1b was also obtained selectively by treatment of

• converts into the orthoester 10 via insertion into the C–O bond. The reaction mechanism for the formation of 8 and 9 comprises the initial attack of the nucleophilic carbene onto the electron-deficient C atom of E-1b to give an intermediate zwitterion 11. The latter undergoes two competitive reactions. The

Conjugated nitrosoalkenes as Michael acceptors in carbon–carbon bond forming reactions: a review and perspective

• Yaroslav D. Boyko,
• Valentin S. Dorokhov,
• Alexey Yu. Sukhorukov and
• Sema L. Ioffe

Beilstein J. Org. Chem. 2017, 13, 2214–2234, doi:10.3762/bjoc.13.220

• reaction with α-bromo ketoximes 1 (Scheme 36). The reaction requires a copper catalyst, which transforms the diazo compound 96 into a metal carbene complex 97. The latter reacts with a nitrosoalkene intermediate NSA (formed from α-bromo ketoxime 1) producing isoxazoline 93 with recovery of the catalyst

NHC-catalyzed cleavage of vicinal diketones and triketones followed by insertion of enones and ynones

• Ken Takaki,
• Makoto Hino,
• Akira Ohno,
• Kimihiro Komeyama,
• Hiroto Yoshida and
• Hiroshi Fukuoka

Beilstein J. Org. Chem. 2017, 13, 1816–1822, doi:10.3762/bjoc.13.176

• Ken Takaki Makoto Hino Akira Ohno Kimihiro Komeyama Hiroto Yoshida Hiroshi Fukuoka Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Kagamiyama, Higashi-Hiroshima 739-8527, Japan 10.3762/bjoc.13.176 Abstract Thiazolium carbene-catalyzed reactions of 1,2

• ; N-heterocyclic carbene; ring enlargement; Stetter reaction; vicinal polyketone; Introduction N-Heterocyclic carbenes (NHCs) have been indispensable catalysts for organic synthesis, particularly for umpolung of various functional groups [1][2][3][4][5][6][7][8][9]. In the Stetter reaction, NHCs

• = C(O)R1) reacted with enones III in the presence of thiazolium carbene catalysts to give double acylation products IV in good yields [15]. If enones can be replaced by ynones III in the reaction with benzils, alkenes IV having three acyl moieties would be formed directly. Related products were

Pd(OAc)₂/Ph₃P-catalyzed dimerization of isoprene and synthesis of monoterpenic heterocycles

• Dominik Kellner,
• Maximilian Weger,
• Andrea Gini and
• Olga García Mancheño

Beilstein J. Org. Chem. 2017, 13, 1807–1815, doi:10.3762/bjoc.13.175

• a bulky monodentated phosphine (Scheme 1, reaction 1) [32]. More recently, important efforts have been made in order to develop new methodologies towards more effective and selective catalytic systems, such as the introduction of highly active N-heterocyclic carbene (NHC) catalysts reported by