Dimerisation, rhodium complex formation and rearrangements of N-heterocyclic carbenes of indazoles

• Zong Guan,
• Jan C. Namyslo,
• Martin H. H. Drafz,
• Martin Nieger and
• Andreas Schmidt

Beilstein J. Org. Chem. 2014, 10, 832–840, doi:10.3762/bjoc.10.79

• strong donor strengths of these indazol-3-ylidenes as already postulated earlier on comparing different stretching frequencies of selected 5-membered NHCs [27] or 13C NMR resonance frequencies of several palladium carbene complexes [28]. We were able to obtain single crystals of 15e to perform an X-ray

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

• using aryl chlorides as the coupling partners and Pd-N-heterocyclic carbene complexes as the catalyst. Finally, as the major by-products are AcOK associated to HBr instead of metallic salts, this procedure is environmentally more attractive than the classical coupling procedures. Experimental The

• crystals. The new complexes were characterized by 1H NMR, 13C NMR, IR and elemental analysis techniques, which support the proposed structures. As described in [49], the air and moisture-stable palladium-carbene complexes (1–9) were soluble in halogenated solvents and insoluble in nonpolar solvents

Metal–ligand multiple bonds as frustrated Lewis pairs for C–H functionalization

• Matthew T. Whited

Beilstein J. Org. Chem. 2012, 8, 1554–1563, doi:10.3762/bjoc.8.177

• character of Fe. In contrast to the silylene and borylene examples presented above, square-planar carbene complexes of iridium(I) often react in a fashion that is dictated by the nucleophilic metal center. An early example of this type of complex was an amidophosphine-supported iridium methylene reported by

• release ethylene and make an iridium(I) trimethylphosphine complex (Scheme 10). More recently, Werner reported several square-planar iridium(I) carbene complexes that react with acid to selectively protonate the iridium center (i.e., the more basic/nucleophilic site) [66][67]. Whited and Grubbs explored

Sequential Au(I)-catalyzed reaction of water with o-acetylenyl-substituted phenyldiazoacetates

• Lei Zhou,
• Yizhou Liu,
• Yan Zhang and
• Jianbo Wang

Beilstein J. Org. Chem. 2011, 7, 631–637, doi:10.3762/bjoc.7.74

• steps. Keywords: alkyne; carbene O–H insertion; cyclization; diazo compounds; gold catalysis; 1H-isochromene; Introduction Transition metal carbene complexes are versatile intermediates and can undergo diverse transformations, including X–H (X = C, O, S, N, etc.) insertions, cyclopropanations, ylide

• formation, and 1,2-migrations [1][2][3][4][5]. Among the various methods to generate metal carbene complexes, transition metal-catalyzed decomposition of diazo compounds is the most straightforward and is highly reliable. Various transition metals have been found to decompose diazo compounds and then

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

• metathesis [4][5][6][7][8][9][10]. It is noteworthy that polymerization of terminal alkynes [11][12][13] and cyclotrimerization of triynes [14][15][16][17][18][19][20] with ruthenium carbene precursors is still a topic of current interest. Then, Fischer tungsten carbene complexes were used by Katz [21], and

• acetylene in the presence of ruthenium carbene complexes has been reported [11]. A challenge that has still to be faced is the EYCM starting from acyclic internal olefins. Selected ruthenium catalysts able to perform EYCM. Applications of EYCM with ethylene in natural product synthesis. Interaction of

Synthesis of Ru alkylidene complexes

• Renat Kadyrov and
• Anna Rosiak

Beilstein J. Org. Chem. 2011, 7, 104–110, doi:10.3762/bjoc.7.14

• ) [13] internal rotation barriers of styrene, 2-vinylthiophene (Ea = 4.8 kcal/mol) [14] and is comparable with rotation barrier of the aryl ring in chromium carbene complexes (ΔG≠298K = 13.0–16.2 kcal/mol) [15]. Experimental Routine, 2D-correlation spectra (1H,1H-COSY) and SELNOE experiments were

Olefin metathesis in nano-sized systems

• Didier Astruc,
• Abdou K. Diallo,
• Sylvain Gatard,
• Liyuan Liang,
• Cátia Ornelas,
• Victor Martinez,
• Denise Méry and
• Jaime Ruiz

Beilstein J. Org. Chem. 2011, 7, 94–103, doi:10.3762/bjoc.7.13

• of catalysts to dendrimers was mostly focused on the recovery of the catalyst. Only a few metallodendritic carbene complexes with covalent binding of the olefin metathesis catalyst are known. Prior to our involvement only compounds with four branches were known [11][12][13][14] but good recyclability

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

• -based [6] catalysts have experienced extensive further developments and improvements. Due to their robustness towards air and moisture, and their comparatively low sensitivity towards functional groups, Ru-carbene complexes have attracted a particularly high degree of attention and “numerous variations

About the activity and selectivity of less well-known metathesis catalysts during ADMET polymerizations

• Hatice Mutlu,
• Lucas Montero de Espinosa,
• Oĝuz Türünç and
• Michael A. R. Meier

Beilstein J. Org. Chem. 2010, 6, 1149–1158, doi:10.3762/bjoc.6.131

• cases isomerization was attributed to the presence of a Ru-hydride species [13][14]. The cause of formation of such Ru-hydride species was long a subject of discussion. Grubbs reported that certain ruthenium carbene complexes can thermally decompose to Ru-hydride species [19]. Moreover, mechanistic

Cross-metathesis of allylcarboranes with O-allylcyclodextrins

• Ivan Šnajdr,
• Zbyněk Janoušek,
• Jindřich Jindřich and
• Martin Kotora

Beilstein J. Org. Chem. 2010, 6, 1099–1105, doi:10.3762/bjoc.6.126

• peracetylation [7][24]. At the outset cross-metathesis of allylcarborane 1a with 2I-O-allylcyclodextrin 2a and various ruthenium-carbene complexes (10 mol %) in dichloromethane was carried out to assess the most suitable catalyst (for cross-metatheses involving carboranes, see: [25][26]). However, when the

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

• . Complexes 2 and 3 were prepared by addition of excess potassium bromide (KBr) or potassium iodide (KI) to a suspension of 1 in methanol, following the procedures for similar transformations of different dichloro carbene complexes to their diiodo analogues [26]. In these cases THF [15][26] or acetone [27

One-pot three-component synthesis of quinoxaline and phenazine ring systems using Fischer carbene complexes

• Priyabrata Roy and
• Binay Krishna Ghorai

Beilstein J. Org. Chem. 2010, 6, No. 52, doi:10.3762/bjoc.6.52

• Priyabrata Roy Binay Krishna Ghorai Department of Chemistry, Bengal Engineering and Science University, Shibpur, Howrah 711103, India 10.3762/bjoc.6.52 Abstract One-pot three-component coupling of o-alkynylheteroaryl carbonyl derivatives with Fischer carbene complexes and dienophiles leading to

• simultaneous one-pot construction of quinoxaline or phenazine rings which occurs in conjunction with the tandem generation and trapping of an azaisobenzofuran intermediate [23][24][25][26]. The synthesis of quinoxaline ring systems involves the coupling of Fischer carbene complexes [27][28][29][30][31][32

• 13A/13B exclusively, in satisfactory yield (Scheme 4). Conclusion We have demonstrated a new route for the tandem generation of furo[3,4-b]pyrazine/ furo[3,4-b]quinoxaline intermediates by the coupling of o-alkynylheteroaryl carbonyl derivatives with Fischer carbene complexes. The intermediates can be

Synthesis of fluorinated δ-lactams via cycloisomerization of gem-difluoropropargyl amides

• Satoru Arimitsu and
• Gerald B. Hammond

Beilstein J. Org. Chem. 2010, 6, No. 48, doi:10.3762/bjoc.6.48

•  tricyclic ring systems [20]. Results and Discussion Initially, we investigated the enyne metathesis reaction of fluorinated enyne 1a with commercially available ruthenium carbene complexes, the Hoveyda–Grubbs second-generation catalyst being the most reactive (entries 1–3, Table 1). The reaction at 110 °C

• by a tandem metathesis reaction, this would permit the synthesis of multi-substituted gem-difluoroisoquinolinones through a subsequent Diels–Alder reaction (eq 2, Scheme 2) [28]. In this regard, we screened various ruthenium carbene complexes using 1,7-enyne amide 1a and styrene 8a as a model

• (Scheme 3). In summary, gem-difluoro-1,7-enyne carbonyl derivatives are useful reaction partners in enyne metathesis cycloisomerization and CM–EYM tandem reactions catalyzed by ruthenium carbene complexes. The resulting diene products can be elaborated further using a Diels–Alder reaction. Comparison 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

• the transient production of A, the first biisobenzofuran. An X-ray crystal structure of meso-3 was obtained. As part of a recent study of the thermal cyclization of η2-(o-ethynylbenzoyl)rhenium complexes to rhenium isobenzofuryl carbene complexes (Scheme 1),[1] we attempted to form a rhenium complex

• isobenzofuryl carbene complexes. Reagents and conditions: (a) Me3SiC≡CH, Pd(PPh3)4, CuI, Et3N, toluene, 40°C, 22 h, 99 %; (b) KF, MeOH, 91 %; (c) 2'-iodoacetophenone, Pd(PPh3)4, CuI, Et3N, toluene, 40°C, 22 h, 62 %; (d) Cp(CO)2Re(THF), THF, 0→22°C, 5 h Possible thermal bicyclization of 1 to A. Thermal