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Synthesis and Photophysical Study of Heteropolycyclic and Carbazole Motif: Nickel-Catalyzed Chelate-Assisted Cascade C-H Activations/Annulations
Herein, nickel-catalyzed synthesis of polyarylcarbazole through sequential C-H bond activations has been described. Regioselective indole C2/C3 functionalization has been achieved in the presence of indole C7-H, which is quite challenging. In addition, this approach also gives easy access to building a heteropolycyclic motif through C6/C7 C-H functionalization of indoline. This methodology is not limited to aromatic internal alkynes as coupling partners; aliphatic alkynes have also shown good tolerance. Notably, during the optimization the catalytic enhancement with sodium iodide as an additive has been observed. We have also studied the photophysical properties of these highly conjugated molecules.
Prusty, Namrata,Banjare, Shyam Kumar,Mohanty, Smruti Ranjan,Nanda, Tanmayee,Yadav, Komal,Ravikumar, Ponneri C.
supporting information
p. 9041 - 9046
(2021/11/30)

One-Pot Tandem ortho-Naphthoquinone-Catalyzed Aerobic Nitrosation of N-Alkylanilines and Rh(III)-Catalyzed C-H Functionalization Sequence to Indole and Aniline Derivatives
The nitroso group served as a traceless directing group for the C-H functionalization of N-alkylanilines, ultimately removed after functioning either as an internal oxidant or under subsequent reducing conditions. The unique ability of o-NQ catalysts to aerobically oxidize the N-alkylanilines without using solvents and stoichiometric amounts of oxidants has rendered the new opportunity to develop the telescoped catalyst systems without a need for directly handling the hazardous N-nitroso compounds.
Si, Tengda,Kim, Hun Young,Oh, Kyungsoo
p. 1152 - 1163
(2021/01/14)

Iodonium Cation-Pool Electrolysis for the Three-Component Synthesis of 1,3-Oxazoles
The synthesis of 1,3-oxazoles from symmetrical and unsymmetrical alkynes was realized by an iodonium cation-pool electrolysis of I2 in acetonitrile with a well-defined water content. Mechanistic investigations suggest that the alkyne reacts with the acetonitrile-stabilized I+ ions, followed by a Ritter-type reaction of the solvent to a nitrilium ion, which is then attacked by water. The ring closure to the 1,3-oxazoles released molecular iodine, which was visible by the naked eye. Also, some unsymmetrical internal alkynes were tested and a regioselective formation of a single isomer was determined by two-dimensional NMR experiments.
Sattler, Lars E.,Hilt, Gerhard
p. 605 - 608
(2020/12/07)

Asymmetric Dearomatization of Indole by Palladium/PC-Phos-Catalyzed Dynamic Kinetic Transformation
A palladium-catalyzed intermolecular dynamic kinetic asymmetric dearomatization of 3-arylindoles with internal alkynes was developed with the use of achiral Xantphos and chiral sulfinamide phosphine ligand (PC-Phos) as the co-ligands. This method could deliver various spiro[indene-1,3′-indole] compounds in good yields (up to 95 % yield) with up to 98 % ee. The salient features of the transformation include the use of readily available substrates, ease of scale-up and the versatile functionalization of the products. The mechanistic experiments gave some insights on active intermediates.
Cheng, Jie,Chu, Haoke,Guo, Yin-Long,Yang, Junfeng,Zhang, Junliang
supporting information
p. 21991 - 21996
(2020/10/02)

Gold(I)-Catalyzed Cross-Coupling Reactions of Arenediazonium Salts with Alkynoic Acids
Abstract: The reaction of simple alkynoate salts with isolated arenediazonium tetrafluoroborate salts that had been pre-conditioned with the gold(I) catalyst AuCl(Me2S) led to the formation of cross-coupled products via a decarboxylative Sonogashira reaction process in modest yield and under mild conditions. The major by-product is a defunctionalized aryl moiety stemming from the diazonium salt, which competitively forms via hydrodediazonation. Good functional group tolerance and reaction site selectivity were attained in this limited investigation.
Abrams, J. N.,Chi, B. K.
p. 1236 - 1244
(2020/09/17)

"canopy Catalysts" for Alkyne Metathesis: Molybdenum Alkylidyne Complexes with a Tripodal Ligand Framework
A new family of structurally well-defined molybdenum alkylidyne catalysts for alkyne metathesis, which is distinguished by a tripodal trisilanolate ligand architecture, is presented. Complexes of type 1 combine the virtues of previous generations of silanolate-based catalysts with a significantly improved functional group tolerance. They are easy to prepare on scale; the modularity of the ligand synthesis allows the steric and electronic properties to be fine-tuned and hence the application profile of the catalysts to be optimized. This opportunity is manifested in the development of catalyst 1f, which is as reactive as the best ancestors but exhibits an unrivaled scope. The new catalysts work well in the presence of unprotected alcohols and various other protic groups. The chelate effect entails even a certain stability toward water, which marks a big leap forward in metal alkylidyne chemistry in general. At the same time, they tolerate many donor sites, including basic nitrogen and numerous heterocycles. This aspect is substantiated by applications to polyfunctional (natural) products. A combined spectroscopic, crystallographic, and computational study provides insights into structure and electronic character of complexes of type 1. Particularly informative are a density functional theory (DFT)-based chemical shift tensor analysis of the alkylidyne carbon atom and 95Mo NMR spectroscopy; this analytical tool had been rarely used in organometallic chemistry before but turns out to be a sensitive probe that deserves more attention. The data show that the podand ligands render a Mo-alkylidyne a priori more electrophilic than analogous monodentate triarylsilanols; proper ligand tuning, however, allows the Lewis acidity as well as the steric demand about the central atom to be adjusted to the point that excellent performance of the catalyst is ensured.
Copéret, Christophe,Fürstner, Alois,Gordon, Christopher P.,Hillenbrand, Julius,Leutzsch, Markus,N?thling, Nils,Wille, Christian,Yiannakas, Ektoras
supporting information
p. 11279 - 11294
(2020/07/13)

Rh(III)-Catalyzed meta-C-H Alkenylation with Alkynes
Rh(III)-catalyzed meta-C-H functionalization reactions are still rare. Herein, we report the first example of Rh(III)-catalyzed meta-C-H alkenylation with disubstituted alkynes directed by a U-shaped nitrile template. Exclusive regio-selectivity has been achieved using unsymmetrical aryl and alkyl-disubstituted alkynes to afford synthetically valuable trisubstituted olefins. Propargyl alcohols are also compatible, affording complex allylic alcohols. Notably, transition metal-catalyzed meta-alkenylation with alkynes has not been successful with Pd catalysts.
Xu, Hua-Jin,Kang, Yan-Shang,Shi, Hang,Zhang, Ping,Chen, You-Ke,Zhang, Bing,Liu, Zhi-Qiang,Zhao, Jing,Sun, Wei-Yin,Yu, Jin-Quan,Lu, Yi
supporting information
p. 76 - 79
(2019/01/11)

Molybdenum Alkylidyne Complexes with Tripodal Silanolate Ligands: The Next Generation of Alkyne Metathesis Catalysts
A new type of molybdenum alkylidyne catalysts for alkyne metathesis is described, which is distinguished by an unconventional podand topology. These structurally well-defined complexes are easy to make on scale and proved to be tolerant toward numerous functional groups; even certain protic substituents were found to be compatible. The new catalysts were characterized by X-ray crystallography and by spectroscopic means, including 95Mo NMR.
Hillenbrand, Julius,Leutzsch, Markus,Fürstner, Alois
supporting information
p. 15690 - 15696
(2019/10/28)

Pd-Catalyzed Alkyne Insertion/C-H Activation/[4 + 2] Carboannulation of Alkenes to the Synthesis of Polycyclics
An unprecedented Pd-catalyzed alkyne insertion/C-H activation/intramolecular [4 + 2] carboannulation of alkenes has been reported. In this transformation, the C-H activation was triggered by an in situ generated alkenylpalladium species via the Pd-catalyzed cross-coupling reaction of aryl iodides and alkynes. Subsequently, the resulting five-membered C, C-palladacycle intermediates were added across the alkenes, providing a unique approach to access diversified polycyclics in good efficiency. Two new rings and three C-C bonds were formed in one pot.
Guo, Songjin,Li, Panpan,Guan, Zhe,Cai, Libo,Chen, Siwei,Lin, Aijun,Yao, Hequan
supporting information
p. 921 - 925
(2019/05/16)

Sequentially Pd/Cu-Catalyzed Alkynylation-Oxidation Synthesis of 1,2-Diketones and Consecutive One-Pot Generation of Quinoxalines
We report a simple and efficient one-pot synthesis of 1,2-diketones by concatenation of two Pd/Cu-catalyzed processes: Pd0/CuI-catalyzed Sonogashira coupling of terminal alkynes with aryl (pseudo)halides furnishes internal alkynes, which are directly transformed by PdII/CuII-catalyzed Wacker-type oxidation with DMSO and oxygen as dual oxidants to furnish 1,2-diketones. With this efficient, catalyst economical process, various aryl iodides and triflates are efficiently transformed in high yields into symmetrically and unsymmetrically substituted 1,2-diketones with various functional groups. This process can be readily extended to a consecutive one-pot synthesis of quinoxalines in a diversity-oriented fashion.
Niesobski, Patrik,Martínez, Ivette Santana,Kustosz, Sebastian,Müller, Thomas J. J.
supporting information
p. 5214 - 5218
(2019/07/31)

Electrochemistry-Enabled Ir-Catalyzed Vinylic C-H Functionalization
Synergistic use of electrochemistry and organometallic catalysis has emerged as a powerful tool for site-selective C-H functionalization, yet this type of transformation has thus far mainly been limited to arene C-H functionalization. Herein, we report the development of electrochemical vinylic C-H functionalization of acrylic acids with alkynes. In this reaction an iridium catalyst enables C-H/O-H functionalization for alkyne annulation, affording α-pyrones with good to excellent yields in an undivided cell. Preliminary mechanistic studies show that anodic oxidation is crucial for releasing the product and regeneration of an Ir(III) intermediate from a diene-Ir(I) complex, which is a coordinatively saturated, 18-electron complex. Importantly, common chemical oxidants such as Ag(I) or Cu(II) did not give significant amounts of the desired product in the absence of electrical current under otherwise identical conditions.
Yang, Qi-Liang,Xing, Yi-Kang,Wang, Xiang-Yang,Ma, Hong-Xing,Weng, Xin-Jun,Yang, Xiang,Guo, Hai-Ming,Mei, Tian-Sheng
supporting information
p. 18970 - 18976
(2019/12/04)

Preparation and Reactions of Mono- and Bis-Pivaloyloxyzinc Acetylides
Mono-pivaloyloxyzinc acetylide and bis-pivaloyloxyzinc acetylide were selectively prepared from ethynylmagnesium bromide in quantitative yields. These zinc reagents readily underwent Negishi cross-couplings with (hetero)aryl iodides or bromides as well as subsequent Sonogashira cross-couplings. 1,3-Dipolar cycloadditions of these zinc acetylides with benzylic azides produced zincated and bis-zincated triazoles which were trapped with several electrophiles. An opposite regioselectivity compared to the Cu-catalyzed click-reactions was observed.
Tüllmann, Carl Phillip,Chen, Yi-Hung,Schuster, Robin J.,Knochel, Paul
supporting information
p. 4601 - 4605
(2018/08/09)

One-Pot Domino Synthesis of Diarylalkynes/1,4-Diaryl-1,3-diynes by [9,9-Dimethyl-4,5-bis(diphenylphosphino)xanthene] (Xantphos)–Copper(I) Iodide–Palladium(II) Acetate-Catalyzed Double Sonogashira-Type Reaction
The low loading combination of the complex [9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene] (Xantphos)copper(I) iodide and simple ligand-free palladium(II) acetate was found to be efficient for the domino synthesis of diarylalkynes by the reaction of aryl halides with trimethylsilylethynylene or bis(trimethylsilyl)acetylene in a single-step procedure. The unsymmetrical diarylalkynes can be obtained through a one-pot two-step approach. The reactions of aryl bromides with 1,4-bis(trimethylsilyl)butadiyne also furnished the corresponding 1,4-diaryl-1,3-diynes in a similar fashion. This route to diarylalkynes and 1,4-diaryl-1,3-diynes is complementary to previously reported synthetic procedures. (Figure presented.).
Qiu, Shaozhong,Zhang, Caiyang,Qiu, Rui,Yin, Guodong,Huang, Jinkun
p. 313 - 321
(2018/01/15)

Preparation method of diaryl acetylene compounds
The invention relates to preparation of an organic compound, and aims to provide a preparation method of diaryl acetylene compounds. The preparation method includes steps of adding associated tribromomethylarene compound and copper in a reactor to perform deoxidizing treatment; dissolving polyamine in a proper amount of anhydrous and oxygen-free solvent, and then adding to the reactor; performingcoupling reaction at 30-80DEG C for 3-12 hours; separating and purifying to obtain diaryl acetylene compounds. The preparation is gentle in synthesis condition and the reaction has good compatibilityto different functional groups; the raw material associated tribromomethylarene compound is convenient to compound and has different substituent groups and variable structure; by adopting one raw material, high-quality product can be obtained through simple treatment, and the output is high; by adopting two different raw materials, the asymmetrical diaryl acetylene compound can be prepared.
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Page/Page column 0076; 0077; 0078; 0091; 0113

(2018/05/16)

Silica-Supported Molybdenum Alkylidyne N-Heterocyclic Carbene Catalysts: Relevance of Site Isolation to Catalytic Performance
The immobilization of the molybdenum alkylidyne complex [(p-OMe-C6H4C≡)Mo(OCMe(CF3)2)3?DME] (DME=1,2-dimethoxyethane) on silica using a silica-supported N-heterocyclic carbene (NHC), that is, 1,3-di(isopropyl)imidazol-2-ylidene, is reported. Two different types of silica, that is, silica 60 and partially dehydroxylated silica 60 obtained via heating to 650 °C (SiO2-650) were used. In both cases, excess silanol groups were end-capped with trimethylsilyl chloride. Immobilization of both the NHC precursor and the metal alkylidyne was followed by 19F magic angle spinning (MAS) and 13C cross-polarization magic angle spinning (CPMAS) NMR and inductively-coupled optical emission spectroscopy (ICP–OES). The metal alkylidyne supported on both types of silica was active in alkyne metathesis and showed activity for a series of functional 2-alkynes. Most importantly, the metal alkylidyne supported on SiO2-650 displayed a substantially higher alkyne metathesis activity than the homogeneous analog or the one supported on regular silica, which is attributed to a site isolation effect and, as a result, reduced bimolecular decomposition.
Hauser, Philipp M.,Hunger, Michael,Buchmeiser, Michael R.
p. 1829 - 1834
(2018/03/13)

Dichotomy of Manganese Catalysis via Organometallic or Radical Mechanism: Stereodivergent Hydrosilylation of Alkynes
Herein, we disclose the first manganese-catalyzed hydrosilylation of alkynes featuring diverse selectivities. The highly selective formation of E-products was achieved by using mononuclear MnBr(CO)5 with the arsenic ligand, AsPh3. Whereas using the dinuclear catalyst Mn2(CO)10 and LPO (dilauroyl peroxide) enabled the reversed generation of Z-products in good to excellent stereo- and regioselectivity. Such a way of controlling the reaction stereoselectivity is unprecedented. Mechanistic experiments revealed the dichotomy of manganese catalysis via organometallic and radical pathways operating in the E- and Z-selective routes, respectively.
Yang, Xiaoxu,Wang, Congyang
supporting information
p. 923 - 928
(2018/01/01)

Surface-Guided Formation of an Organocobalt Complex
Organocobalt complexes represent a versatile tool in organic synthesis as they are important intermediates in Pauson-Khand, Friedel-Crafts, and Nicholas reactions. Herein, a single-molecule-level investigation addressing the formation of an organocobalt c
Weber, Peter B.,Hellwig, Raphael,Paintner, Tobias,Lattelais, Marie,Paszkiewicz, Mateusz,Casado Aguilar, Pablo,Deimel, Peter S.,Guo, Yuanyuan,Zhang, Yi-Qi,Allegretti, Francesco,Papageorgiou, Anthoula C.,Reichert, Joachim,Klyatskaya, Svetlana,Ruben, Mario,Barth, Johannes V.,Bocquet, Marie-Laure,Klappenberger, Florian
supporting information
p. 5754 - 5759
(2016/05/09)

Dual gold/photoredox-catalyzed C(sp)-H arylation of terminal alkynes with diazonium salts
The arylation of alkyl and aromatic terminal alkynes by a dual gold/photoredox catalytic system is described. Using aryldiazonium salts as readily available aryl sources, a range of diversely-functionalized arylalkynes could be synthesized under mild, base-free reaction conditions using visible light from simple household sources or even sunlight. This process, which exhibits a broad scope and functional group tolerance, expands the range of transformations amenable to dual gold/photoredox catalysis to those involving C-H bond functionalization and demonstrates the potential of this concept to access AuI/AuIII redox chemistry under mild, redox-neutral conditions.
Tlahuext-Aca, Adrian,Hopkinson, Matthew N.,Sahoo, Basudev,Glorius, Frank
p. 89 - 93
(2015/12/30)

Highly Active Multidentate Ligand-Based Alkyne Metathesis Catalysts
Alkyne metathesis catalysts composed of molybdenum(VI) propylidyne and multidentate tris(2-hydroxylbenzyl)methane ligands have been developed, which exhibit excellent stability (remains active in solution for months at room temperature), high activity, an
Du, Ya,Yang, Haishen,Zhu, Chengpu,Ortiz, Michael,Okochi, Kenji D.,Shoemaker, Richard,Jin, Yinghua,Zhang, Wei
supporting information
p. 7959 - 7963
(2016/06/09)

Catalysts for the alkyne metathesis
Organometallic compounds of the general formula (I), in which M=Mo, W, are claimed.
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Page/Page column 22; 23; 24; 38; 39

(2015/04/15)

Hydrazone-palladium catalyzed annulation of 1-allyl-2-bromobenzene derivatives with internal alkynes
Annulation of 1-allyl-2-bromobenzene derivatives with internal alkynes using a hydrazone-palladium catalyst system proceeded smoothly and gave the corresponding polysubstituted naphthalene derivatives in good to high yields.
Watanabe, Kohei,Mino, Takashi,Hatta, Chikako,Ito, Shisei,Sakamoto, Masami
supporting information
p. 11645 - 11650
(2015/12/08)

"quick and click" assembly of functionalised indole rings via metal-promoted cyclative tandem reactions
An efficient and convenient synthesis of a variety of decorated indoles using a three-component tandem metal-catalysed process is described. We propose here a new "synthetic kit" that allows for the "quick and click" assembly of indole rings using readily available, and inexpensive starting materials under environmentally friendly reaction conditions. This journal is
Capitta, Francesca,De Luca, Lidia,Porcheddu, Andrea
p. 59297 - 59301
(2015/02/19)

Microwave-enhanced cross-coupling reactions involving alkynyltrifluoroborates with aryl bromides
Palladium-catalyzed alkynylation has emerged as one of the most reliable methods for the synthesis of alkynes which are often used in natural product syntheses and material science. An efficient method for coupling alkynyltrifluoroborates with various aryl bromides in the presence of a palladium catalyst has been developed using microwave irradiation. The microwave reactions are rapid and efficient.
Coltuclu, Vitali,Dadush, Eric,Naravane, Abhijit,Kabalka, George W.
p. 1755 - 1761
(2013/04/10)

Palladium-free synthesis of unsymmetrical diarylethynes by cross-coupling reaction of alkynylboronates with aryl iodides catalyzed by CuCl
A series of unsymmetrical diarylethynes have been synthesized by the copper-catalyzed cross-coupling reaction of alkynylboronates with aryl iodides in high to excellent yields under palladium-free conditions. A wide range of substrates bearing an electron-donating or an electron-withdrawing substituent on the aromatic ring are compatible with this reaction.
Ogawa, Daisuke,Li, Jing,Suetsugu, Masato,Jiao, Jiao,Iwasaki, Masayuki,Nishihara, Yasushi
p. 518 - 521
(2013/02/23)

Single-molecule conductance of functionalized oligoynes: Length dependence and junction evolution
We report a combined experimental and theoretical investigation of the length dependence and anchor group dependence of the electrical conductance of a series of oligoyne molecular wires in single-molecule junctions with gold contacts. Experimentally, we focus on the synthesis and properties of diaryloligoynes with n = 1, 2, and 4 triple bonds and the anchor dihydrobenzo[b]thiophene (BT). For comparison, we also explored the aurophilic anchor group cyano (CN), amino (NH2), thiol (SH), and 4-pyridyl (PY). Scanning tunneling microscopy break junction (STM-BJ) and mechanically controllable break junction (MCBJ) techniques are employed to investigate single-molecule conductance characteristics. The BT moiety is superior as compared to traditional anchoring groups investigated so far. BT-terminated oligoynes display a 100% probability of junction formation and possess conductance values which are the highest of the oligoynes studied and, moreover, are higher than other conjugated molecular wires of similar length. Density functional theory (DFT)-based calculations are reported for oligoynes with n = 1-4 triple bonds. Complete conductance traces and conductance distributions are computed for each family of molecules. The sliding of the anchor groups leads to oscillations in both the electrical conductance and the binding energies of the studied molecular wires. In agreement with experimental results, BT-terminated oligoynes are predicted to have a high electrical conductance. The experimental attenuation constants βH range between 1.7 nm-1 (CN) and 3.2 nm-1 (SH) and show the following trend: β H(CN) H(NH2) H(BT) H(PY) ≈ βH(SH). DFT-based calculations yield lower values, which range between 0.4 nm -1 (CN) and 2.2 nm-1 (PY).
Moreno-Garcia, Pavel,Gulcur, Murat,Manrique, David Zsolt,Pope, Thomas,Hong, Wenjing,Kaliginedi, Veerabhadrarao,Huang, Cancan,Batsanov, Andrei S.,Bryce, Martin R.,Lambert, Colin,Wandlowski, Thomas
supporting information
p. 12228 - 12240
(2013/09/23)

Synthesis of unsymmetrically disubstituted ethynes by the palladium/copper(I)-cocatalyzed sila-Sonogashira-Hagihara coupling reactions of alkynylsilanes with aryl iodides, bromides, and chlorides through a direct activation of a carbon-silicon bond
In this paper, we explore the copper/palladium-cocatalyzed cross-coupling reactions of 1-aryl-2-trimethylsilylethynes with aryl iodides, bromides, and chlorides as coupling partners, to furnish unsymmetrically disubstituted ethynes in moderate to excellent yields. Various aryl iodides were subjected to reaction under the optimized conditions with 5 mol % of Pd(PPh3) 2 and 50 mol % of CuCl. The steric properties of the aryl iodide proved more influential to the outcome of the cross-coupling reaction than electronic factors. In addition, we succeeded in synthesizing unsymmetrical diarylethynes using two different aryl iodides in one-pot. Furthermore, under the same reaction conditions with 10 mol % of PdCl2, 40 mol % of P(4-FC6H4)3, and 50 mol % of CuCl as catalyst, we succeeded in synthesizing unsymmetrical diarylethynes from various aryl bromides. Finally, we explored reactions with aryl chlorides and duly discovered that unsymmetrical diarylethynes were obtainable in moderate to good yields when 10 mol % of Pd(OAc)2, 10 mol % of (-)-DIOP, and 10 mol % of CuCl were used. These reactions proceed through a direct activation of a carbon-silicon bond in alkynylsilanes by CuCl to generate the corresponding alkynylcopper species via transmetalation from silicon to copper. Mechanistic investigations on the reaction of alkynylsilanes with aryl bromides confirmed that the trimethylsilyl bromide generated in situ retarded both transmetalation steps between CuCl and alkynylsilane, and between palladium(II) species formed by oxidative addition and alkynylcopper species.
Nishihara, Yasushi,Inoue, Eiji,Noyori, Shintaro,Ogawa, Daisuke,Okada, Yoshiaki,Iwasaki, Masayuki,Takagi, Kentaro
experimental part
p. 4869 - 4881
(2012/08/08)

Optimized synthesis, structural investigations, ligand tuning and synthetic evaluation of silyloxy-based alkyne metathesis catalysts
Nitride- and alkylidyne complexes of molybdenum endowed with triarylsilanolate ligands are excellent (pre)catalysts for alkyne-metathesis reactions of all sorts, since they combine high activity with an outstanding tolerance toward polar and/or sensitive functional groups. Structural and reactivity data suggest that this promising application profile results from a favorable match between the characteristics of the high-valent molybdenum center and the electronic and steric features of the chosen Ar3SiO groups. This interplay ensures a well-balanced level of Lewis acidity at the central atom, which is critical for high activity. Moreover, the bulky silanolates, while disfavoring bimolecular decomposition of the operative alkylidyne unit, do not obstruct substrate binding. In addition, Ar3SiO groups have the advantage that they are more stable within the coordination sphere of a high-valent molybdenum center than tert-alkoxides, which commonly served as ancillary ligands in previous generations of alkyne metathesis catalysts. From a practical point of view it is important to note that complexes of the general type [(Ar3SiO)3Mo≡X] (X = N, CR; R = aryl, alkyl, Ar = aryl) can be rendered air-stable with the aid of 1,10-phenanthroline, 2,2'-bipyridine or derivatives thereof. Although the resulting adducts are themselves catalytically inert, treatment with Lewis acidic additives such as ZnCl2 or MnCl2 removes the stabilizing N-donor ligand and gently releases the catalytically active template into the solution. This procedure gives excellent results in alkyne metathesis starting from air-stable and hence user-friendly precursor complexes. The thermal and hydrolytic stability of representative molybdenum alkylidyne and -nitride complexes of this series was investigated and the structure of several decomposition products elucidated. Active yet tamed: Molybdenum benzylidyne complexes endowed with triarylsilanolates as ancillary ligands are superbly active and exquisitely selective alkyne metathesis catalysts, but can be rendered air-stable by reversible complexation with 1,10-phenanthroline or 2,2'-bipyridine (see, e.g., figure). A systematic molecular editing of their basic structural motif furnished a "library" of such catalysts and gave detailed insights into the parameters determining their favorable application profile. Copyright
Heppekausen, Johannes,Stade, Robert,Kondoh, Azusa,Seidel, Guenter,Goddard, Richard,Fuerstner, Alois
supporting information; scheme or table
p. 10281 - 10299
(2012/10/08)

Synthesis and antimalarial activities of a diverse set of triazole-containing furamidine analogues
Four different series of triazole diamidines have been prepared by the Pinner method from the corresponding triazole dinitriles. Copper-catalyzed "click chemistry" was used for the synthesis of 1,4- and 4,5-substituted triazoles, aryl magnesium acetylide
Berger, Olivier,Kaniti, Archana,van Ba, Christophe Tran,Vial, Henri,Ward, Stephen A.,Biagini, Giancarlo A.,Bray, Patrick G.,O'Neill, Paul M.
experimental part
p. 2094 - 2108
(2012/06/18)

Symmetric diarylacetylenes: One-pot syntheses and solution photoluminescence
Bis(tri-n-butylstannyl)acetylene was synthesized and used to create a series of symmetric diarylacetylenes via a one-step Stille coupling protocol with Pd(PPh3)4 as the catalyst. In many cases, the product simply crystallized in good yields from the reaction mixture upon cooling after reflux at 100 °C or upon removal of solvent. The diarylacetylenes were studied using UV-vis and fluorescence spectroscopies, which showed that naphthyl- and biphenyl-substituted acetylenes had very high solution-state fluorescence quantum yields.
Brown, Amy E.,Eichler, Barrett E.
supporting information; experimental part
p. 1960 - 1963
(2011/04/25)

Pd- and Ni-catalyzed cross-coupling reactions of functionalized organozinc reagents with unsaturated thioethers
A variety of unsaturated thioethers have been subjected to cross-coupling reactions with functionalized zinc reagents in the presence of a transition-metal catalyst. Three different catalytic systems based on Pd(OAc)2 or [Ni(acac)2] and the ligands S-Phos or DPE-Phos gave the best results. N-Heterocyclic thioethers based on a pyridine, pyrimidine, pyrazine, pyridazine, triazine, benzothiazole, benzoxazole, pyrrole, or quinazoline ring, as well as thiomethylacetylenes, serve as electrophiles in this cross-coupling reaction. Aryl-, heteroaryl-, benzylic, and alkylzinc halides with sensitive functionalities, such as ester, nitrile, or ketone groups react at ambient temperature with unsaturated thioethers using a Ni catalyst. The corresponding Pd-catalyzed reactions require slightly higher temperatures. Large-scale cross-coupling experiments (10-20 mmol) with N-heterocycles are also reported.
Melzig, Laurin,Metzger, Albrecht,Knochel, Paul
supporting information; experimental part
p. 2948 - 2956
(2011/04/16)

Electronic effects of ruthenium-catalyzed [3+2]-cycloaddition of alkynes and azides
A combined experimental and theoretical study of ruthenium-catalyzed azide-alkyne cycloaddition (RuAAC) reactions is presented and various electronic analyses were conducted to provide a basis in understanding the observed regioselectivity of the 1,2,3-triazole products. Computational studies using density functional theory (DFT) and atoms in molecules quantum theory (AIM) further yield fresh details on the electronic factors that determine the regioselectivity in the RuAAC. It is found that the formation of 1,2,3-triazole products is irreversible and from the Hammett study, the pathway involving a vinyl cationic intermediate is ruled out. The electronic effect favors the formation of 5-electron-donating-group substituted-1,2,3-trizoles.
Hou, Duen-Ren,Kuan, Ting-Chun,Li, Yu-Kai,Lee, Richmond,Huang, Kuo-Wei
experimental part
p. 9415 - 9420
(2011/01/12)

Palladium/copper-catalyzed sila-Sonogashira reactions of aryl iodides with alkynylsilanes via a direct C-Si bond activation
The palladium-catalyzed cross-coupling reactions of aryl iodides with alkynylsilanes in the presence of a substoichiometric amount (50 mol %) of copper(I) chloride as an activator in DMF under strictly non-basic reaction conditions afford the corresponding unsymmetrical diarylethynes in moderate to excellent yields. A wide range of substrates bearing an electron-donating or an electron-withdrawing substituent on the aromatic ring are compatible.
Nishihara, Yasushi,Inoue, Eiji,Ogawa, Daisuke,Okada, Yoshiaki,Noyori, Shintaro,Takagi, Kentaro
scheme or table
p. 4643 - 4646
(2009/10/04)

Efficient synthesis of thioamide terminated molecular wires
Bis-thioamide terminated 'molecular wires' are formed in a high yield under mild conditions from readily synthesised bis-nitrile terminated molecules and aqueous ammonium sulfide in DMF.
Dixon, Sally,Whitby, Richard J.
p. 8147 - 8150
(2007/10/03)

Highly Active Trialkoxymolybdenum(VI) Alkylidyne Catalysts Synthesized by A Reductive Recycle Strategy
A systematic study of alkyne metathesis catalyzed by trialkoxymolybdenum(VI) alkylidyne complexes is reported, in which substrate functional groups, alkynyl substituents, and catalyst ligands are varied. Sterically hindered trisamidomolybdenum(VI) propylidyne complex 5 was prepared conveniently through a previously communicated reductive recycle strategy. Alcoholysis of 5 with various phenols/alcohols provides a set of active catalysts for alkyne metathesis at room temperature, among which the catalyst with p-nitrophenol as ligand shows the highest catalytic activity and is compatible with a variety of functional groups and solvents. A key finding that enabled the use of highly active molybdenum(VI) catalysts is replacement of the commonly used propynyl substituents on the starting alkyne substrates with butynyl groups. Under reduced pressure using 1,2,4-trichlorobenzene as an involatile solvent, the alkyne metathesis of butynyl substituted compounds proceeds well at 30 °C providing high yields (83%-97%) of dimers. Rationalization of the special role played by butynyl substrates is discussed.
Zhang, Wei,Kraft, Stefan,Moore, Jeffrey S.
p. 329 - 335
(2007/10/03)

Alkyne metathesis: Development of a novel molybdenum-based catalyst system and its application to the total synthesis of epothilone A and C
Sterically hindered molybdenum(III) amido complexes of the general type [Mo{(tBu)(Ar)N}3] (1), upon treatment with CH2Cl2 or other halogen donors, have been converted into highly effective catalysts for all kinds of alkyne metathesis reactions. Although the actual nature of the propagating species formed in situ is still elusive, halogen transfer to the Mo center of 1 plays a decisive role in the activation of such precatalysts. It was possible to isolate and characterize by X-ray crystallography some of the resulting molybdenum halide derivatives such as 15, 16 and 20 which themselves were shown to be catalytically active. Numerous applications illustrate the performance of the catalytic system 1/CH2Cl2 which operates under mild conditions and tolerates an array of polar functional groups. The wide scope allows the method to be implemented into the total synthesis of sensitive and polyfunctional natural products. Most notable among them is a concise entry into the potent anticancer agents epothilone A (86) and C (88). The macrolide core of these targets is forged by ring closing alkyne metathesis (RCAM) of diyne 113, followed by Lindlar hydrogenation of cycloalkyne 114 thus formed. Since this strategy opens a stereoselective entry into (Z)-alkene 115, the approach is inherently more efficient than previous syntheses based on conventional RCM. Wiley-VCH Verlag GmbH, 2001.
Fuerstner, Alois,Mathes, Christian,Lehmann, Christian W.
p. 5299 - 5317
(2007/10/03)

Alkyne cross metathesis reactions of extended scope
equation presented A catalyst formed in situ from Mo[N(t-Bu)(Ar)]3 1 (Ar = 3,5-dimethylphenyl) and CH2Cl2 in toluene effects cross metathesis reactions of functionalized alkynes that are beyond reach of more traditional promotors. An application to the synthesis of prostaglandin E2 (PGE2) 19 and the acetylated PGE derivative 18b shows the compatibility of this method with sensitive substrates.
Fuerstner, Alois,Mathes, Christian
p. 221 - 223
(2007/10/03)

Coupling reactions of alkynylsilanes mediated by a Cu(I) salt: Novel syntheses of conjugate diynes and disubstituted ethynes
Reaction of 1-trimethylsilylalkyne with copper(I) chloride in a polar solvent, DMF, at 60 °C under an aerobic conditions smoothly undergoes homo- coupling to give the corresponding symmetrical 1,3-butadiynes in 70-99% yields. In addition, (arylethynyl)trimethylsilanes are found to couple with aryl triflates and chlorides in the presence of Cu(I)/Pd(0) (10 mol %/5 or 10 mol %) cocatalyst system to give the corresponding diarylethynes in 49-99% yields. The cross-coupling reaction is applied to a one-pot synthesis of the corresponding unsymmetrical diarylethynes from (trimethylsilyl)ethyne via sequential Sonogashira-Hagihara and the present cross-coupling reactions using two different aryl triflates. The reactions of (arylethynyl)trimethylsilanes with aryl(chloro)ethynes in the presence of 10 mol % of CuCl also yield the corresponding unsymmetrical 1,3-butadiynes in 43-97% yields.
Nishihara, Yasushi,Ikegashira, Kazutaka,Hirabayashi, Kazunori,Ando, Jun-Ichi,Mori, Atsunori,Hiyama, Tamejiro
p. 1780 - 1787
(2007/10/03)

Alkyne metathesis with simple catalyst systems: High yield dimerization of propynylated aromatics; scope and limitations
High yield dimerization of propynylated benzenes and propynylnaphthalene by a mixture of Mo(CO)6 and 4-chlorophenol at 140 °C in 1,2-dichlorobenzene is reported to give the corresponding disubstituted alkynes. The scope and limitation of the reaction and the influence of substitution pattern and substitution type are discussed. Oxygen or nitrogen carrying substrates metathesize in moderate to good yields and ortho-alkyl substituted examples form the respective tolanes very efficiently.
Pschirer, Neil Gregory,Bunz, Uwe H. F.
p. 2481 - 2484
(2007/10/03)

SYNTHESIS OF SYMMETRICAL TOLANES FROM BENZILIDENE BROMIDES
The main relationships govering the formation of symmetrical tolanes during the condensation of benzylidene bromides under the influence of strong bases in dipolar aprotic solvents were investigated.The reaction takes place through the formation of α,α'-dibromostilbenes, which are debrominated to tolanes under these conditions.
Vernigor, E. M.,Shalaev, V. K.,Luk'yanets, E. A.
p. 317 - 321
(2007/10/02)