Stereochemistry of ring-opening/cross metathesis reactions of exo- and endo-7-oxabicyclo[2.2.1]hept-5-ene-2-carbonitriles with allyl alcohol and allyl acetate

• Piotr Wałejko,
• Michał Dąbrowski,
• Lech Szczepaniak,
• Jacek W. Morzycki and
• Stanisław Witkowski

Beilstein J. Org. Chem. 2015, 11, 1893–1901, doi:10.3762/bjoc.11.204

• allyl acetate promoted by different ruthenium alkylidene catalysts were studied. The stereochemical outcome of the reactions was established. The issues concerning chemo- (ROCM vs ROMP), regio- (1-2- vs 1-3-product formation), and stereo- (E/Z isomerism) selectivity of reactions under various conditions

• ROCM reactions of exo- and endo-7-oxabicyclo[2.2.1]hept-5-en-2-carbonitrile (1 and 2, respectively) with allyl acetate (3) or allyl alcohol (4) catalyzed by several commercially available ruthenium catalysts ([Ru]1–6, Figure 1). To the best of our knowledge there is no example of a ROCM reaction of 7

• . Furthermore, less complex mixtures of products were formed and they were easier to separate from the ROMP products. 7-Oxanorbornenes 1 and 2 were treated with olefin 3 or 4 in the presence of ruthenium catalysts [Ru]1–6 (Figure 1) to afford mixtures of tetrahydrofurans 5–12 (Scheme 2). The mixtures were

Profluorescent substrates for the screening of olefin metathesis catalysts

• Raphael Reuter and
• Thomas R. Ward

Beilstein J. Org. Chem. 2015, 11, 1886–1892, doi:10.3762/bjoc.11.203

• . To demonstrate the validity of the approach, four commercially available ruthenium-metathesis catalysts were evaluated in six different solvents. The results from the fluorescent assay agree well with HPLC conversions, validating the usefulness of the approach. Keywords: fluorescence; microplate

Cross metathesis of unsaturated epoxides for the synthesis of polyfunctional building blocks

• Meriem K. Abderrezak,
• Kristýna Šichová,
• Nancy Dominguez-Boblett,
• Antoine Dupé,
• Zahia Kabouche,
• Christian Bruneau and
• Cédric Fischmeister

Beilstein J. Org. Chem. 2015, 11, 1876–1880, doi:10.3762/bjoc.11.201

• compounds. The resulting cross metathesis products were hydrogenated in a tandem fashion employing the residual ruthenium from the metathesis step as the hydrogenation catalyst. Interestingly, the epoxide ring remained unreactive toward this hydrogenation method. The saturated compound resulting from the

• cross metathesis of 1 with methyl acrylate was transformed by means of nucleophilic ring-opening of the epoxide to furnish a diol, an alkoxy alcohol and an amino alcohol in high yields. Keywords: cross metathesis; epoxide; ruthenium catalysts; tandem reactions; Introduction Catalytic carbon–carbon

• necessary to ensure high conversion. Reactions were carried out in dimethyl carbonate (DMC), a solvent compatible with ruthenium olefin metathesis catalysts [28] while being much greener than toluene or dichloromethane commonly used in such reactions [29]. Based on our previous results and observations in

Recent applications of ring-rearrangement metathesis in organic synthesis

• Sambasivarao Kotha,
• Milind Meshram,
• Priti Khedkar,
• Shaibal Banerjee and
• Deepak Deodhar

Beilstein J. Org. Chem. 2015, 11, 1833–1864, doi:10.3762/bjoc.11.199

• % yield [51]. The regioselective formation of 240 may be attributed to the facile formation of a Ru–carbene intermediate where the metal participates on the side opposite to that of the methyl ester and thereby minimizing the steric crowding between ruthenium and carbonyl oxygen of an ester functionality

• RRM process and this activity will continue with more vigour in the future. Ruthenium alkylidene catalysts used in RRM processes. General representation of various RRM processes. A general mechanism for RRM process. RRM of cyclopropene systems. RRM of cyclopropene with catalyst 2. (i) catalyst 2 (2.5

Nitro-Grela-type complexes containing iodides – robust and selective catalysts for olefin metathesis under challenging conditions

• Andrzej Tracz,
• Mateusz Matczak,
• Katarzyna Urbaniak and
• Krzysztof Skowerski

Beilstein J. Org. Chem. 2015, 11, 1823–1832, doi:10.3762/bjoc.11.198

• vicinity of ruthenium related to the presence of iodides ensures enhanced catalyst stability. The benefits are most apparent under challenging conditions, such as very low reaction concentrations, protic solvents or with the occurrence of impurities. Keywords: green solvents; macrocyclization; metathesis

• ; ruthenium; Introduction Olefin metathesis (OM) is a mild and versatile catalytic method which allows the formation of carbon–carbon double bonds [1]. Understanding the key events in ruthenium-catalyzed olefin metathesis [2] and developing efficient and selective catalysts [3] provides opportunities for

• interest. Currently, the second generation Hoveyda-type catalysts, such as HII [4], A [5], B [6], and C [7] are considered to be the most versatile tool for OM (Figure 1). Modifications of ligands permanently bound to the ruthenium center appear to be the most efficient methods for altering the catalyst

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

• , China 10.3762/bjoc.11.194 Abstract Ruthenium complexes [Ru(L1)2(CH3CN)2](PF6)2 (1), [RuL1(CH3CN)4](PF6)2 (2) and [RuL2(CH3CN)3](PF6)2 (3) (L1= 3-methyl-1-(pyrimidine-2-yl)imidazolylidene, L2 = 1,3-bis(pyridin-2-ylmethyl)benzimidazolylidene) were obtained through a transmetallation reaction of the

• molecular structures of the complexes 4 and 5 were also studied by X-ray diffraction analysis. These ruthenium complexes have proven to be efficient catalysts for transfer hydrogenation of various ketones. Keywords: N-heterocyclic carbene; ruthenium; transfer hydrogenation; Introduction N-Heterocyclic

• [8][9][10][11][12][13][14][15][16] have been reported. In the family of metal complexes supported by functionalized NHCs, ruthenium complexes have long been a research focus on various applications such as catalysis and photochemistry [17][18][19][20][21][22][23][24][25][26]. However, the majority of

A comprehensive study of olefin metathesis catalyzed by Ru-based catalysts

• Albert Poater and
• Luigi Cavallo

Beilstein J. Org. Chem. 2015, 11, 1767–1780, doi:10.3762/bjoc.11.192

• species is also discussed, with either pyridine or phosphine ligands to dissociate. Keywords: cis; density functional theory (DFT); N-heterocyclic carbene; olefin metathesis; ruthenium; Introduction Organic synthesis is based on reactions that drive the formation of carbon–carbon bonds [1]. Olefin

• metathesis represents a metal-catalyzed redistribution of carbon–carbon double bonds [2][3][4][5][6] and provides a route to unsaturated molecules that are often challenging or impossible to prepare by any other means. Furthermore, the area of ruthenium-catalyzed olefin metathesis reactions is an outstanding

• . Possible side or bottom mechanism of the insertion of the olefin. Ruthenium catalysts, bottom-bound (a) or side-bound (b and c). Studied systems. Binding energy, in kcal/mol, of the first, E1, and of the second, E2, pyridine/PMe3 molecule to the naked 14e species 1–13. Energies (E) in kcal/mol, of the

Grubbs–Hoveyda type catalysts bearing a dicationic N-heterocyclic carbene for biphasic olefin metathesis reactions in ionic liquids

• Maximilian Koy,
• Hagen J. Altmann,
• Benjamin Autenrieth,
• Wolfgang Frey and
• Michael R. Buchmeiser

Beilstein J. Org. Chem. 2015, 11, 1632–1638, doi:10.3762/bjoc.11.178

• solvent (toluene) and the ionic liquid (IL) 1-butyl-2,3-dimethylimidazolium tetrafluoroborate [BDMIM+][BF4−]. The structure of Ru-2 was confirmed by single crystal X-ray analysis. Keywords: biphasic catalysis; ionic initiators; recycling; ROMP; ruthenium; Introduction Ionic metathesis catalysts offer

• both the IL and the ionic catalyst effectively block any crossover of catalyst into the second (organic) phase. This offers access to metathesis reactions in which the products have a low ruthenium contamination [11]. Equally important, reactions can be run under biphasic, continuous conditions

• applying supported ionic liquid phase (SILP) technology [11]. We recently reported on different Ru-based ionic metathesis catalysts that can be used for these purposes. In these systems, the charge is either located directly at the ruthenium [11][12] or at the 1-methylpyridinium-4-carboxylate ligands that

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

• Cedex, France 10.3762/bjoc.11.169 Abstract A silver-free methodology was developed for the synthesis of unprecedented N-heterocyclic carbene ruthenium indenylidene complexes bearing a bidentate picolinate ligand. The highly stable (SIPr)(picolinate)RuCl(indenylidene) complex 4a (SIPr = 1,3-bis(2-6

• . Keywords: latent catalyst; olefin metathesis; picolinate ligand; ruthenium indenylidene; Introduction Olefin metathesis has witnessed tremendous development in the last decades and has emerged as a powerful tool with dramatic impact on both organic chemistry and materials science [1][2]. Intensive

• research has notably allowed for the design of efficient ruthenium-based catalysts that exhibit improved reactivity [3][4][5][6]. On the other hand, some applications require a precatalyst that can remain inert towards substrates and only initiate in response to a specific stimulus [7]. A common strategy

Ruthenium indenylidene “1^st generation” olefin metathesis catalysts containing triisopropyl phosphite

• Stefano Guidone,
• Fady Nahra,
• Alexandra M. Z. Slawin and
• Catherine S. J. Cazin

Beilstein J. Org. Chem. 2015, 11, 1520–1527, doi:10.3762/bjoc.11.166

• -type ligands. Keywords: 1st generation; indenylidene; metathesis; phosphite; ruthenium; Introduction The olefin metathesis reaction is a powerful tool for C–C bond formation in the synthesis of highly valuable organic compounds [1][2][3][4]. Protocols involving W-, Mo- and Ru-based pre-catalysts can

• ruthenium complexes used in olefin metathesis reactions. Molecular structure of mixed phosphine/phosphite complex 1. Hydrogen atoms are omitted for clarity. Molecular structure of 2 and the ylide 3. Hydrogen atoms and solvent molecules are omitted for clarity. Selected bond distances (Å) and angles (°) (ESD

Design and synthesis of hybrid cyclophanes containing thiophene and indole units via Grignard reaction, Fischer indolization and ring-closing metathesis as key steps

• Sambasivarao Kotha,
• Ajay Kumar Chinnam and
• Mukesh E. Shirbhate

Beilstein J. Org. Chem. 2015, 11, 1514–1519, doi:10.3762/bjoc.11.165

• of the starting material leading to a complex mixture of products as indicated by thin-layer chromatography (TLC). It is known that sulfur can coordinate with the ruthenium catalyst and deactivate the catalytic cycle [35][36][37]. Therefore, the diolefin did not undergo the RCM sequence. Next, we

The enantioselective synthesis of (S)-(+)-mianserin and (S)-(+)-epinastine

• Piotr Roszkowski,
• Jan. K. Maurin and
• Zbigniew Czarnocki

Beilstein J. Org. Chem. 2015, 11, 1509–1513, doi:10.3762/bjoc.11.164

• : chiral diamines; enantioselective reduction; epinastine; mianserin; ruthenium complexes; Introduction Mianserin (1) is a tetracyclic compound widely used as a drug in the treatment of depression. Despite the fact that the (S)-(+)-enantiomer of mianserin is more potent than the (R)-antipode in

• ruthenium complex 11 which contain (1R,2R)- or (1S,2S)-N-tosyl-1,2-cyclohexanediamine as chiral ligand (Figure 2). The reaction was carried out in acetonitrile using an azeotropic mixture of formic acid/triethylamine as hydrogen source with 50:1 substrate to catalyst ratio. Under these conditions the

• regardless of the solvent used, with the exception of acetonitrile (Table 1, entries 8–10). In CH3CN this catalyst is inactive and the product was not formed. The solvent effect on the chemical yield was similar to that observed with catalyst 11 (Table 1). Finally, the ruthenium complex 13 modified with

Tandem cross enyne metathesis (CEYM)–intramolecular Diels–Alder reaction (IMDAR). An easy entry to linear bicyclic scaffolds

• Javier Miró,
• María Sánchez-Roselló,
• Álvaro Sanz,
• Fernando Rabasa,
• Carlos del Pozo and
• Santos Fustero

Beilstein J. Org. Chem. 2015, 11, 1486–1493, doi:10.3762/bjoc.11.161

• bearing two different olefin units one being an α,β-unsaturated moiety, the tandem CM–IMDAR protocol would initiate on the electronically neutral olefin. Furthermore, those dienes could undergo an intramolecular cyclization (RCM) promoted by the ruthenium carbene that would compete with the desired

• 5 (method A) or acyl chlorides 6 (method B) under standard conditions (Scheme 3). Since the basic indole nitrogen in substrate 8f could interfere with the ruthenium catalyst, it was N-methylated to render compound 8g. With substrates 8 in hand, they were subjected to the optimized conditions of the

Thermal properties of ruthenium alkylidene-polymerized dicyclopentadiene

• Yuval Vidavsky,
• Yotam Navon,
• Yakov Ginzburg,
• Moshe Gottlieb and
• N. Gabriel Lemcoff

Beilstein J. Org. Chem. 2015, 11, 1469–1474, doi:10.3762/bjoc.11.159

• proportional to the resting period and was accompanied by a constant increase in the glass-transition temperature. We hypothesize that a relaxation mechanism within the cross-linked scaffold, together with a long-lived stable ruthenium alkylidene species are responsible for the observed phenomenon. Keywords

• : glass-transition temperature; polydicyclopentadiene; ring opening metathesis polymerization; ruthenium-catalyzed olefin metathesis; thermoset polymers; Introduction Olefin metathesis [1][2][3][4][5][6] has advanced to become a major synthetic tool in academia [7][8][9][10][11] and industry [12

• ) (Figure 1). The Grubbs-type ruthenium initiators, known for their high activity, stability and functional group tolerance are extensively used to promote this type of olefin metathesis reactions. For example, the Grubbs second generation catalyst 2 [18] (Figure 1), may be used to initiate ROMP reactions

Consequences of the electronic tuning of latent ruthenium-based olefin metathesis catalysts on their reactivity

• Karolina Żukowska,
• Eva Pump,
• Aleksandra E. Pazio,
• Krzysztof Woźniak,
• Luigi Cavallo and
• Christian Slugovc

Beilstein J. Org. Chem. 2015, 11, 1458–1468, doi:10.3762/bjoc.11.158

• Arabia 10.3762/bjoc.11.158 Abstract Two ruthenium olefin metathesis initiators featuring electronically modified quinoline-based chelating carbene ligands are introduced. Their reactivity in RCM and ROMP reactions was tested and the results were compared to those obtained with the parent unsubstituted

• reactivity of the complexes. Keywords: DFT calculations; olefin metathesis; ring closing metathesis; ring-opening metathesis polymerisation; ruthenium; Introduction Olefin metathesis is a catalytic process during which C–C double bonds are exchanged [1]. Since the first examples were published in the 1950s

• , many stunning accomplishments have been made in the field resulting in ever increasing interests in the method. Establishment of well-defined molybdenum- and ruthenium-based complexes lead to multitude of applications [2][3][4]. Especially, the latter class of compounds have gained attention due to

Cross-metathesis reaction of α- and β-vinyl C-glycosides with alkenes

• Ivan Šnajdr,
• Kamil Parkan,
• Filip Hessler and
• Martin Kotora

Beilstein J. Org. Chem. 2015, 11, 1392–1397, doi:10.3762/bjoc.11.150

• ; catalysis; carbohydrates; cross-metathesis; ruthenium; Introduction Natural and unnatural C-substituted glycosides are important compounds with a plethora of attractive biological properties and they often have been used as artificial DNA components [1]. Among various synthetic procedures providing C

Tetrathiafulvalene-based azine ligands for anion and metal cation coordination

• Awatef Ayadi,
• Aziz El Alamy,
• Olivier Alévêque,
• Magali Allain,
• Nabil Zouari,
• Mohammed Bouachrine and
• Abdelkrim El-Ghayoury

Beilstein J. Org. Chem. 2015, 11, 1379–1391, doi:10.3762/bjoc.11.149

• spectrum observed for other anions. Synthesis and crystal structure of a neutral rhenium complex Few metal complexes based on ruthenium cations have been previously prepared with dinitrophenylazine type ligands [48][49]. These reports indicate that the pyridinedinitrophenylazine type ligands are good

Surprisingly facile CO₂ insertion into cobalt alkoxide bonds: A theoretical investigation

• Willem K. Offermans,
• Claudia Bizzarri,
• Walter Leitner and
• Thomas E. Müller

Beilstein J. Org. Chem. 2015, 11, 1340–1351, doi:10.3762/bjoc.11.144

• cycloaddition. Direct catalytic carboxylation of aliphatic compounds and arenes by rhodium(I)– and ruthenium(II)–pincer complexes, respectively. Insertion of carbon dioxide into a metal–oxygen bond via a cyclic four-membered transition state. R is either an aliphatic or aromatic group. Facile CO2 uptake by zinc

Design and synthesis of fused polycycles via Diels–Alder reaction and ring-rearrangement metathesis as key steps

• Sambasivarao Kotha and
• Ongolu Ravikumar

Beilstein J. Org. Chem. 2015, 11, 1259–1264, doi:10.3762/bjoc.11.140

• used to design new polycycles. In this regard, ruthenium alkylidene catalysts are effective in realizing the RRM of bis-norbornene derivatives prepared by DA reaction and Grignard addition. Here, fused polycycles are assembled which are difficult to produce by conventional synthetic routes. Keywords

• ; HRMS (Q–ToF) m/z: [M + Na]+ calcd for C25H32NaO2, 387.2295; found, 387.2292. Commercially available ruthenium catalysts used in RRM metathesis. Crystal structure of 5 with thermal ellipsoids drawn at 50% probability level. Synthesis of hexacyclic compound 6a by using an RRM approach. Synthesis of

Interactions between tetrathiafulvalene units in dimeric structures – the influence of cyclic cores

• Huixin Jiang,
• Virginia Mazzanti,
• Christian R. Parker,
• Søren Lindbæk Broman,
• Jens Heide Wallberg,
• Karol Lušpai,
• Adam Brincko,
• Henrik G. Kjaergaard,
• Anders Kadziola,
• Peter Rapta,
• Ole Hammerich and
• Mogens Brøndsted Nielsen

Beilstein J. Org. Chem. 2015, 11, 930–948, doi:10.3762/bjoc.11.104

• [11][12] have shown how rotamers can indeed influence the electronic coupling in bis-ruthenium complexes separated by oligoynediyl spacers. In addition, an increased interaction between redox centres upon linking them together in cyclic structures was previously observed in ferrocene-dimers [13]. Here

Further exploration of the heterocyclic diversity accessible from the allylation chemistry of indigo

• Alireza Shakoori,
• John B. Bremner,
• Mohammed K. Abdel-Hamid,
• Anthony C. Willis,
• Rachada Haritakun and
• Paul A. Keller

Beilstein J. Org. Chem. 2015, 11, 481–492, doi:10.3762/bjoc.11.54

• ' reagent. This is not unexpected as there are reports of ruthenium-based species catalysing Claisen rearrangements [7] including a similar RCM–Claisen sequence in 2,2'-bis(allyloxy)-1,1'-binaphthyls and O,O'-(but-2-en-1,4-diyl) binaphthols [12][13]. Additionally, examples of C2 to C3 Claisen rearrangement

Ruthenium-catalyzed C–H activation of thioxanthones

• Danny Wagner and
• Stefan Bräse

Beilstein J. Org. Chem. 2015, 11, 431–436, doi:10.3762/bjoc.11.49

• /bjoc.11.49 Abstract Thioxanthones – being readily available in one step from thiosalicylic acid and arenes – were used in ruthenium-catalyzed C–H-activation reaction to produce 1-mono- or 1,8-disubstituted thioxanthones in good to excellent yields. Scope and limitation of this reaction are presented

Eosin Y-catalyzed visible-light-mediated aerobic oxidative cyclization of N,N-dimethylanilines with maleimides

• Zhongwei Liang,
• Song Xu,
• Wenyan Tian and
• Ronghua Zhang

Beilstein J. Org. Chem. 2015, 11, 425–430, doi:10.3762/bjoc.11.48

• light, which is clean, abundant, and renewable. The pioneering work in this research area, reported by the groups of MacMillan [7][8][9], Yoon [10][11], Stephenson [12][13] and others [14][15][16][17][18], has demonstrated that ruthenium and iridium complexes as visible light photoredox catalysts are

• capable of catalyzing a broad range of useful reactions. A variety of new methods have been developed to accomplish known and new chemical transformations by means of these transition metal-based photocatalysts so far. However, the ruthenium and iridium catalysts usually are high-cost, potentially toxic

Cross-dehydrogenative coupling for the intermolecular C–O bond formation

• Igor B. Krylov,
• Vera A. Vil’ and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2015, 11, 92–146, doi:10.3762/bjoc.11.13

• -containing moieties (amide, pyridine, oxime, etc.) are most commonly used as directing groups, which are responsible for the regioselectivity of the C–O coupling. Most transformations of this type are catalyzed by Pd(II) compounds. Examples of the use of copper and ruthenium compounds as catalysts were also

• [55], and O-acetyl aryl oximes [56] in the presence of the Pd(OAc)2/PhI(OAc)2 system were described. The ruthenium-catalyzed ortho-acyloxylation of acetanilides 39 with carboxylic acids in the presence of AgSbF6 and ammonium persulfate afforded products 40 (Scheme 8) [57]. This method can be used for

• halides were used as oxidants. Ruthenium, iridium, and palladium complexes acted as catalysts. In most cases, structurally simple alcohols, which are taken in a large excess relative to the CH-reagent, served as OH-reagents. The exception is a study [95], in which the coupling was accomplished using an

Morita–Baylis–Hillman reaction of acrylamide with isatin derivatives

• Radhey M. Singh,
• Kishor Chandra Bharadwaj and
• Dharmendra Kumar Tiwari

Beilstein J. Org. Chem. 2014, 10, 2975–2980, doi:10.3762/bjoc.10.315

• appending other functionalities/groups for intramolecular transformations. Other reports have used this feature for the development of an intramolecular MBH reaction: Corey et al. (total synthesis) [29], Pigge et al. (ruthenium complexes as an electrophile) [30], and Basavaiah et al. [31][32]. Isatin has