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In the presence of 2.5 mol % of Pd2(dba)3 and 5 mol % of PPh3, nearly equimolar mounts of dimethyl nona-2,7-diyne-1,9-dioate derivatives and dimethyl acetylenedicarboxylate (DMAD) were reacted in toluene at 110 °C to give

(η6-Hexaalkylbenene)(η4-naphthalene)iron- and (η6-hexaalkylbenzene)(η4-1,4-dimethylnaphthalene)iron-complexes (alkyl=methyl and ethyl) can be prepared from bis(ethylene)(toluene)iron, the desired naphthalene der

The palladium-catalyzed reaction of 4-iodo-2-quinolones with activated alkynes was investigated. Cyclopenta[de]quinoline-2(1 H)-ones and/or phenanthridine-6(5 H)-ones were obtained through [3+2] annulation involving aromatic C?H activation or [2+2+2] annulation involving vinylic C?H activation, respectively. Reasonable mechanisms for the formation of these annulation products have been proposed based on density functional theory calculations.

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The reactions of Ru3(CO)12 with alkynyl ketones R1CCC(O)R2 (R1 = Et, R2 = Me (1); R1 = Ph, R2 = Me (2); R1 = n-hexyl, R2 = Ph (3); R1 = H, R2 = CH3 (4); and R1 = C(O)OCH3, R2 = OCH3 (5)) proceeds in toluene with the formation of three ruthenoles (1a-3a), four CO-inserted binuclear clusters (1b-2b, 1c and 3c), a tetranuclear cluster 4a, a binuclear cluster 5a and a cyclotrimerization product 5b. Clusters 1a-3a, 1b, 2b, 1c and 3c were isolated from the reactions of Ru3(CO)12 with two equivalents of the corresponding ketones 1-3; 4a and 5a were collected by adding 4 and 5 to Ru3(CO)12 in molar ratios of 1:1 and 1:3, respectively; 5b was obtained by adding 5 to 5a in a molar ratio of 2:1. All compounds were characterized by NMR, FT-IR, and MS-ESI, and most of them were structurally verified by single crystal X-ray diffraction. Although the reaction products of 1-3 and Ru3(CO)12 exhibit similar cluster frameworks of usual ruthenoles and CO-inserted binuclear clusters, the isolation of the clusters 1b-2b, 1c and 3c reveals their strong dependence on both electronic and steric effects of the substituents of the 1,3-ynones 1-3. In addition, detailed investigations suggested that the high reactivity of the terminal hydrogen atom and electron-withdrawing property of the carbonyl group in 4 play a key role in the formation of 4a, and that the structurally unusual 5a is an intermediate in the formation of 5b.

One-pot ring-closing enyne metathesis and Diels-Alder reactions led to efficient synthesis of tricyclic and tetracyclic β-lactams.

Direct, efficient, selective, and catalytic all describe the synthesis of conjugated dienes from two molecules of alkyne, an organic halide, and tetramethyltin with 1 mol% of a (1,2-diimine)palladium complex in DMF (see the catalytic cycle involving Pd0. Pd(II) and Pd(IV) species on the right) Palladium-phosphane complexes do not catalyze this reaction. Furthermore, 1,4-dihalo-l,3-dienes were synthesized stoichiometrically from alkynes and molecular halogen.

(Chemical Equation Presented) A concise, three-step synthesis of 1,4,8,11-substituted 2,3,9,-10-tetrakis(methoxycarbonyl)pentacenes from commercially available 1,2,4,5-tetrakis(bromomethyl)benzene was established. Efficient alkynylation, followed by formation of four fused rings via a zirconacyclopentadiene intermediate, and then oxidation with DDQ gave pentacenes 1a-c. The process was compatible with methyl, phenyl, and trimethylsilyl substituents, which have good solubility in various organic solvents.

Crossing paths with rhodium: A cationic RhI/H8-BINAP complex has been found to catalyze the linear cross-trimerization of terminal alkynes, acetylenedicarboxylates, and acrylamides to give substituted trienes. The asymmetric linear c

The reaction between the bis(ethylene) complex [TpRh(C2H4)2], 1, (Tp=hydrotris(pyrazolyl)borate), and dimethyl acetylenedicarboxylate (DMAD) has been studied under different experimental conditions. A mixture of products was formed, in which TpRhIspecies were prevalent, whereas the presence of trapping agents, like water or acetonitrile, allowed for the stabilization and isolation of octahedral TpRhIIIcompounds. An excess of DMAD gave rise to a small amount of the [2+2+2] cyclotrimerization product hexamethyl mellitate (6). Although no catalytic application of 1 was achieved, mechanistic insights shed light on the formation of stable rhodium species representing the resting state of the catalytic cycle of rhodium-mediated [2+2+2] cyclo(co)trimerization reactions. Metallacyclopentene intermediate species, generated from the activation of one alkyne and one ethylene molecule from 1, and metallacyclopentadiene species, formed by oxidative coupling of two alkynes to the rhodium centre, are crucial steps in the pathways leading to the final organometallic and organic products.

The cascade cyclization reactions of 1,5-bisallenes grant access to a great variety of products by precisely tuning the catalyst system and/or the reagents involved. Herein, we present our findings that 1,5-bisallenes react with two molecules of dimethyl acetylenedicarboxylate to afford, in a completely diastereoselective manner, cis-3,4-arylvinyl pyrrolidines and cyclopentanes. DFT calculations have been used to postulate a mechanism for the developed reaction which encompasses a [2+2+2] cycloaddition reaction of the two alkynes and the external double bond of one allene, followed by a cycloisomerization involving the internal double bond of the second allene. (Figure presented.).

A case study on the effect of the employment of two different NHC ligands in complexes [Ni(NHC)2] (NHC=iPr2ImMe 1Me, Mes2Im 2) and their behavior towards alkynes is reported. The reaction of a mixture of [Ni2(iPr2ImMe)4(μ-(η2 : η2)-COD)] B/ [Ni(iPr2ImMe)2(η4-COD)] B’ or [Ni(Mes2Im)2] 2, respectively, with alkynes afforded complexes [Ni(NHC)2(η2-alkyne)] (NHC=iPr2ImMe: alkyne=MeC≡CMe 3, H7C3C≡CC3H7 4, PhC≡CPh 5, MeOOCC≡CCOOMe 6, Me3SiC≡CSiMe3 7, PhC≡CMe 8, HC≡CC3H7 9, HC≡CPh 10, HC≡C(p-Tol) 11, HC≡C(4-tBu-C6H4) 12, HC≡CCOOMe 13; NHC=Mes2Im: alkyne=MeC≡CMe 14, MeOOCC≡CCOOMe 15, PhC≡CMe 16, HC≡C(4-tBu-C6H4) 17, HC≡CCOOMe 18). Unusual rearrangement products 11 a and 12 a were identified for the complexes of the terminal alkynes HC≡C(p-Tol) and HC≡C(4-tBu-C6H4), 11 and 12, which were formed by addition of a C?H bond of one of the NHC N-iPr methyl groups to the C≡C triple bond of the coordinated alkyne. Complex 2 catalyzes the cyclotrimerization of 2-butyne, 4-octyne, diphenylacetylene, dimethyl acetylendicarboxylate, 1-pentyne, phenylacetylene and methyl propiolate at ambient conditions, whereas 1Me is not a good catalyst. The reaction of 2 with 2-butyne was monitored in some detail, which led to a mechanistic proposal for the cyclotrimerization at [Ni(NHC)2]. DFT calculations reveal that the differences between 1Me and 2 for alkyne cyclotrimerization lie in the energy profile of the initiation steps, which is very shallow for 2, and each step is associated with only a moderate energy change. The higher stability of 3 compared to 14 is attributed to a better electron transfer from the NHC to the metal to the alkyne ligand for the N-alkyl substituted NHC, to enhanced Ni-alkyne backbonding due to a smaller CNHC?Ni?CNHC bite angle, and to less steric repulsion of the smaller NHC iPr2ImMe.

A cyclic tri-nuclear α-diimine nickel(0) complex [{Ni(μ-LMe-2,4)}3] (2) was synthesized from a “pre-organized”, trimerized trigonal LNiBr2-type precursor [Ni3(μ2-Br)3(μ3-Br)2(LMe-2,4)3]·Br (1; LMe-2,4 = [(2,4-Me2C6H3)NC(Me)]2). In complex 2, the α-diimine ligands not only exhibit the normal N,N′-chelating mode, but they also act as bridges between the Ni atoms through an unusual π-coordination of a C═N bond to Ni. Complex 2 is able to catalyze the cyclotrimerization of alkynes to form substituted benzenes in good yield and regio-selectivity for the 1,3,5-isomers, which is found to vary with the nature of the alkyne employed. This complex represents a convenient self-supported nickel(0) catalyst with no need for additional ligands and reducing agent.

A persulfate-promoted metal-free route in water toward the synthesis of unprecedented polyfunctionalized benzenes is reported. In our approach, the targeted products are delivered in high to moderate yields from phenylacetylenes and α,β-unsaturated compounds via the benzannulation reaction. This method has a good scope and gives access to functionalized benzene rings that offer a wealth of opportunities for further functionalization.

Tetrahydroisoquinoline (THIQ) is a key structural component in many biologically active molecules including natural products and synthetic pharmaceuticals. Here, we report on the use of transition-metal mediated [2 + 2 + 2] cyclotrimerisation of alkynes to generate tricyclic THIQs with potential to selectively inhibit AKR1C3.

Cobalt-catalyzed alkyne cyclotrimerization and crossed [2 + 2 + 2] cycloadditions are developed in a plug flow reactor. The protocol generally uses 5 mol % of Co2(CO)8 and is scalable at least at multigram scale. Efficient and scalable use of Co2(CO)8 for crossed reactions of diynes and alkynes has hardly any precedent.

A reaction of potassium hepta(methoxycarbonyl)cycloheptatrienide with chlorine and bromine gave high yields of the corresponding chloroand bromohepta(methoxycarbonyl)cycloheptatrienes; the fluoro derivative was obtained by the exchange reaction of the corresponding bromide with silver fluoride. In contrast to the mentioned halides, the iodo derivative has proved unstable. Thermolysis of bromohepta(methoxycarbonyl)cycloheptatriene was studied, as well as its conversion to the azido and methoxy derivatives upon treatment with NaN3 or methanol.

A series of bis-thiourea-functionalized [n]polynorbornane hosts (1-6) with increasing size were synthesized and their anion-binding properties were evaluated by using 1HNMR spectroscopic titration and Job's plot analysis. The larger bis-thiourea-[3]polynorbornane scaffolds 4 and 5 bound acetate in a 1:1 (cooperative) arrangement, whereas the corresponding smaller norbornane host 2, identical in preorganization, bound acetate in a 1:2 (independent) arrangement. In contrast, the size of the framework had no influence on the binding of dihydrogenphosphate. These results clearly highlight the subtle influence that the framework itself can have on host-guest interactions. One anion or two? A series of bis-thiourea-functionalized [n]polynorbornane hosts (1-6) with increasing size were synthesized and their anion-binding properties were evaluated by using 1HNMR spectroscopic titration and Job's plot analysis. Our results highlight the subtle influence that the framework itself can have on host-guest interactions.

An effective regioselective cyclotrimerization of terminal alkynes is achieved by the direct utilization of NiCl2·6H2O, Zn, and 2-(benzimidazolyl)-6-(1-(arylimino)ethyl)pyridine in one step under ambient temperature.

The 16-electron (16e) half-sandwich complex CpCo(S2C 2B10H8)(CHCHCO2Me)2 (1; Cp = cyclopentadienyl) was considered as inert owing to hindered di-substitution at B sites. However in methanol complex 1 reacts with ethynylferrocene (FcCCH) and dimethyl acetylenedicarboxylate (DMAD, MeO2CCCCO2Me) to lead to two-fold alkyne insertion at Co-S bond to give rise to unusual stable 18e adduct CpCo(S2C2B10H8) (CHCHCO2Me)2(HCCFc)(MeO2CCCCO2Me) (2) containing mixed alkynes. Also in methanol complex 1 undergoes intramolecular hydrogen transfer of one CHCHCO2Me unit to adjacent carbon to form a CH2CCO2Me unit, thus producing the 18e complex CpCo(S2C2B10H8)[CH 2CCO2Me][CHCHCO2Me] (3). Further investigation indicates that complex 1 can catalyze [2 + 2 + 2] cycloaddition of alkynes. The catalytic efficiency is determined by temperature and nature of alkynes. In THF in the presence of [N(n-Bu)4]Br complex 1 is transformed to ionic complex [N(n-Bu)4]+[Co(S2C2B 10H8)2(CHCHCO2Me)4] - (4), in which metal-dithiolene is planar. Analogous [N(n-Bu) 4]+[Co(S2C2B10H 9)2(CHCHCO2Me)2]- (5) was also synthesized from mono-substituted precursor CpCo(S2C 2B10H9)(CHCHCO2Me) (1′). The electrochemical properties of both 4 and 5 show significant positive shift of redox peaks versus the analogous bis(1,2-benzenedithiolato)cobaltate (III) (Co(bdt)2). Reactivity of both neutral 16e CpCo complexes and ionic metal-dithiolene derivatives declines with the increase of substituents on carborane cage. All the new compounds have been characterized by NMR, IR, mass spectrometry, elemental analysis, and 2, 3, and 4 have been structurally characterized by X-ray diffraction.

Thermal decomposition of 1-(4-methoxyphenyl)- and 1-(4-fluorophenyl) hepta(methoxycarbonyl)-3a,7a-dihydroindazoles at 135 C in the presence of allyl or propargyl halides leads to the elimination of hexamethyl benzenehexacarboxylate and the formation of the corresponding pyrazolines or pyrazoles as the products of 1,3-dipolar cycloaddition of 1-aryl-3- methoxycarbonylnitrilimines to the multiple bonds of the substrates used. In the case of vinyl halides, the products of the target reactions are either obtained in low yields or nonexistent, with a side conversions taking place instead. Thus, for example, in the case of 1,1-dichloro-4-methylpenta-1,3-diene, besides hexamethyl benzenehexacarboxylate, 3,5,5-trichloro-2-methylpent-4-en-2-ol and arylchlorohydrazones MeO2CC(Cl)=N-NHAr were unexpectedly isolated as the main products, as well.

Artificially mimicking the cyclase phase of terpene biosynthesis inspires the invention of new methodologies, since working with carbogenic frameworks containing minimal functionality limits the chemist's toolbox of synthetic strategies. For example, the construction of terpene skeletons from five-carbon building blocks would be an exciting pathway to mimic in the laboratory. Nature oligomerizes, cyclizes, and then oxidizes γ,γ-dimethylallyl pyrophosphate (DMAPP) and isopentenyl pyrophosphate (IPP) to all of the known terpenes. Starting from isoprene, the goal of this work was to mimic Nature's approach for rapidly building molecular complexity. In principle, the controlled oligomerization of isoprene would drastically simplify the synthesis of terpenes used in the medicine, perfumery, flavor, and materials industries. This article delineates our extensive efforts to cooligomerize isoprene or butadiene with alkynes in a controlled fashion by zerovalent nickel catalysis building off the classic studies by Wilke and co-workers.

Intermolecular [2+2+2] cycloaddition reaction employing an air-stable ruthenium perchloro-cyclobutenonyl complex as a catalyst is reported. A series of internal alkynes were incorporated with dimethyl acetylene-dicarboxylate in a ratio of 1:2 to give vari

Thermal treatment of the trinuclear ruthenium complex {μ2- η5:η1-(C5H4N)(C 9H5)}Ru3(CO)9 (1) with 1 equiv of diphenylacetylene gave the trinuclear complex {μ3- η1:η2:η5-(C5H 4N)(C9H5)(PhC-CPh)}Ru3(CO) 7 (2) via the insertion of an alkyne into the Ru-C(η1) bond of 1. Complex 2 could be transformed into the dinuclear and trinuclear complexes {μ2-η1:η5-(C 5H4N)(C9H5)(PhC-CPh)}Ru 2(CO)2(μ2-η2: η4-CPh-CPhCPh-CPh) (3), {μ3-η2: η3:η5-(C5H4N)(C 9H5)(CPhCPh-CPhCPh)}Ru3(CO)6 (4), and {μ2-η1:η5-(C5H 4N)(C9H5)(PhC-CPh)}Ru3(CO) 4(μ3-η2-PhC-CPh)2 (5) in the presence of excess diphenylacetylene. Similarly, reaction of 1 with 1 equiv of phenylacetylene gave the alkyne-inserted product {μ3- η1:η2:η5-(C5H 4N)(C9H5)(HC-CPh)}Ru3(CO) 7 (6), which could also react with excess phenylacetylene to give the complexes {μ3-η2:η4: η5-(C5H4N)(C9H 5)(C-CPhCH-CPh)}(μ2-H)Ru3(CO)6 (7) and {μ2-η2:η4-(C 5H4N)(C9H6)(C-CPhCH-CPh)}Ru 2(CO)4(μ2-CO) (8). Complex 7 could be transformed slowly into 8 in refluxing toluene. The reactions of 3-(2-pyridyl)indene with internal alkynes catalyzed by Ru3(CO) 12 and 1 were also tested, obtaining several C-H/alkyne coupling products, while the reaction with phenylacetylene did not work under the same conditions. The molecular structures of 2-8 were determined by X-ray diffraction.

CpCo(CO)2 catalyzes the cocyclization of ortho- diethynylthiophenes and -pyridines with alkynes to construct the corresponding thia- and azaphenylenes. This strategy is applied to the synthesis of linear 1-aza[3]phenylene, the first higher heterophenylene. Georg Thieme Verlag Stuttgart.

Functionalized biaryl derivatives have been prepared by applying [2+2+2] cyclotrimerization with the aid of Grubbs first-generation catalyst (G-I). The trimerized products were subjected to the Suzuki-Miyaura cross-coupling reaction sequence to generate h

The combination of cationic rhodium(I) complexes with N-phosphino tert-butylsulfinamides (PNSO) ligands is efficient for catalytic intra- and intermolecular [2+2+2] cycloaddition reactions. PNSO ligands are a new class of chiral bidentate ligands, which h

Cyclopentadienyl-ruthenium half-sandwich complexes with η2-bound alkyne ligands have been suggested as catalytic intermediates in the early stages of Ru-catalyzed reactions with alkynes. We show that electronically unsaturated complexes of the formula [RuCl(Cp)(η2-RC=CR')] can be stabilized and crystallized by using the sterically demanding cyclopentadienyl ligand Cp (Cp = η5-l-methoxy-2,4tert-butyl-3-neopentyl-cyclopentadienyl). Furthermore we demonstrate that [RuCl2(Cp)]2 is an active and regioselective catalyst for the [2+2+2] cyclotrimerization of alkynes. The first elementary steps of the reaction of mono(η2- alkyne) complexes containing {RuCl(Cp*)} (Cp* = η5- C5Me5) and (RuCl(Cp)} fragments with alkynes were investigated by DFT calculations at the M06/6-31G* level in combination with a continuum solvent model. Theoretical results are able to rationalize and complement the experimental findings. The presence of the sterically demanding Cp ligand increases the activation energy required for the formation of the corresponding di(η2alkyne) complexes, enhancing the initial regioselectivity, but avoiding the evolution of the system towards the expected cyclotrimerization product when bulky substituents are present. Theoretical results also show that the electronic structure and stability of a metallacyclic intermediate is strongly dependent on the nature of the substituents present in the alkyne.

Disclosed is a process for production of a substituted benzene, which comprises intramolecularly and/or intermolecularly trimerizing a triple bond in an alkyne in the presence of a transition metal catalyst to yield a substituted benzene compound. In the process, the transition metal catalyst is prepared from an iminomethylpyridine represented by the formula (1) or (2), a transition metal salt or a hydrate thereof, and a reducing agent in a reaction system and is used to perform the trimerization. The process can be used in any one of the intramolecular cyclization of a triyne compound, the cyclization of a diyne compound or an alkyne compound and the intermolecular cyclization of three molecules of an alkyne compound, is excellent in economic effectiveness and operability, and is practically advantageous. wherein R1 and R3 independently represent a linear or cyclic C1-C20 aliphatic hydrocarbon group or the like; R2 represents a hydrogen atom or the like; X represents a hydrogen atom, O or the like; and Y represents O, S or the like.

Ruthenium-catalyzed substitutions of carbon pronucleophiles, various [2+2+2] cycloadditions, and addition of a diazo compound to an alkyne are shown to proceed in the presence of air. Notably diverse catalytic manifolds remain supported under conditions generally regarded as prohibitive. Building on rare reports from the literature we show that a range of organometallic transformations based on reaction intermediates derived from (C5Me5)Ru or (C5H5)Ru moieties are air-compatible.

Cobalt cyclopentadienyl complexes incorporating a fumarate and a CO ligand (see picture) efficiently catalyze inter-and intramolecular [2+2+2] cycloadditions of alkynes, nitriles, and/or alkenes to give benzenes, pyridines, or 1,3-cyclohexadienes. Unlike catalysts such as [CpCo (CO)2] or [CpCo(C2H4)2] (Cp=C5H5), they are air-stable, easy to handle, compatible with microwave conditions, and do not necessarily require irradiation to be active.

Selected [2+2+2] cycloadditions, alkene-alkyne coupling and fusion of enyne with diazo compound, all triggered by an artificial organometallic ruthenium catalyst are demonstrated to proceed under ambient aerobic aqueous conditions in presence of bodily fl

(Chemical Equation Presented) The two conditions for the preparation of the reactive N-(tert-butoxycarbonyl)indolo-2,3-quinodimethane intermediate were developed by the reaction of the N-(tert-butoxycarbonyl)-2-(1- ethoxycarbonyloxymethylallenyl) aniline

A novel and efficient approach towards the synthesis of poly-substituted diphenylalkane derivatives have been demonstrated using a strategic combination of [2+2+2] cyclotrimerization, ethylene cross-enyne metathesis and Diels-Alder reaction as key steps.

New heteroscorpionate ligands (1 and 2) having a di(pyridin-2-yl)(1H-pyrrol-2-yl)methane substructure are synthesized. X-ray crystallographic analysis on 1 and 2 reveals that they form unique hydrogen bonding networks depending on the size of neighboring

The RhCl3·3H2O/i-Pr2NEt-catalyzed [2+2+2] cyclotrimerization of alkynes has been achieved. The reaction can be widely used for various alkynes and provides tri- or hexa-substituted benzenes regioselectively in high yields. The [2+2+2] cycloaddition of diynes and alkynes is also developed, and it affords benzene derivatives in moderate to high yields.

Reaction of [Ru3(CO)12] with tri(2-furyl)phosphine, P(C4H3O)3, at 40 °C in the presence of a catalytic amount of Na[Ph2CO] furnishes two triruthenium complexes [Ru3(CO)10{P(C4H3O)3}2] (1) and [Ru3(CO)9{P(C4H3O)3}3] (2) with the ligand coordinated through the phosphorus atom. Treatment of 1 and 2 with Me3NO at 40 °C affords the dinuclear phosphido-bridged complexes [Ru2(CO)6(μ-η1,η2-C4H3O){μ-P(C4H3O)2}] (3) and [Ru2(CO)5(μ-η1,η2-C4H3O){μ-P(C4H3O)2}{P(C4H3O)3}] (4), respectively, that are formed via phosphorus-carbon bond cleavage of a coordinated phosphine followed by coordination of the dissociated furyl moiety to the diruthenium center in a σ,π-alkenyl mode. Reaction of [Ru3(CO)12] with tri(2-furyl)phosphine in refluxing benzene gives, in addition to 3 and 4, low yields of the cyclometallated complex [Ru3(CO)9{μ-η1,η1-P(C4H3O)2(C4H2O)}2] (5). Treatment of 3 with EPh3 (E = P, As, Sb) at room temperature yields the monosubstituted derivatives [Ru2(CO)5(μ-η1,η2-C4H3O){μ-P(C4H3O)2}(EPh3)] (E = P, 8; E = As, 9; E = Sb, 10). Similar reactions of 3 with P(C4H3O)3, P(OMe)3 and ButNC yield 4, [Ru2(CO)5(μ-η1,η2-C4H3O){μ-P(C4H3O)2}{P(OMe)3}] (11) and [Ru2(CO)5(μ-η1,η2-C4H3O){μ-P(C4H3O)2}(NCBut)] (12), respectively. The molecular structures of complexes 3, 4 and 8 have been elucidated by single crystal X-ray diffraction studies. Each complex contains a bridging σ,π-alkenyl group and while in 4 the phosphine is bound to the σ-coordinated metal atom, in 8 it is at the π-bound atom. Protonation of 3 and 4 gives the hydride complexes [(μ-H)Ru2(CO)6(μ-η1,η2-C4H3O){μ-P(C4H3O)2}]+ (6) and [(μ-H)Ru2(CO)5(μ-η1,η2-C4H3O){μ-P(C4H3O)2}{P(C4H3O)3}]+ (7), respectively, while heating 3 with dimethylacetylenedicarboxylate (DMAD) in refluxing toluene gives the cyclotrimerization product, C6(CO2Me)6.

Several highly substituted naphthalenes 3 have been synthesized in a one-pot reaction by treatment of arenes 1 with alkynes 2 in the presence of palladium acetate and silver acetate. In this Pd-catalyzed protocol, an arene provides a benzo source for the construction of a naphthalene core through twofold aryl C - H bond activation. Reaction of triphenylphosphine with diphenylethyne (2 a) under the catalysis of PdIV complexes produced 1,2,3,4-tetraphenylnaphthalene (3ba) in 62% yield. Here, triphenylphosphine undergoes one aryl C - P bond cleavage and one aryl C - H bond activation to serve as a benzo moiety. Crystal structures of cycloadducts 3ea, 3ga, and 3ac have been analyzed. The twisted naphthalenes arise not only from the overcrowded substituents but also from the contribution of the CH3-π interaction.

A new route to the synthesis of a trans-tris(bicyclo[2.2.1]hexeno)benzene derivative, using Diels-Alder reaction as critical step, was investigated. The compound with six methoxycarbonyl groups was successfully synthesized in good yield without any organometallic reagents. Some useful by-products from dimethyl but-2-ynedioate were also isolated from the last step. Perhaps due to stereo-hindrance or electrostatic repulsion in the cis-isomer, trans-isomer was found to be the only isomer in the crystal and its structure was proved by X-ray diffraction.

Mesoporous graphitic C3N4 was successfully employed as an effective catalyst for the cyclotrimerisation of various nitriles into triazine derivatives and the cyclisation of functional alkynes. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

A 2-(2,6-diisopropylphenyl)iminomethylpyridine (1a)/CoCl 2·6H2O/Zn reagent has been developed as an effective instant catalyst for the intra- and intermolecular cyclotrimerization of alkynes to substituted benzenes, making the method

The dimeric bis(allyl)-ruthenium(IV) complex [{Ru(η3:η3-C10H16)(μ-Cl)Cl}2] (C10H16 = 2,7-dimethylocta-2,6-diene-1,8-diyl) was found to catalyze efficiently the [2 + 2 + 2] cyclization of terminal and internal alkynes in aqueous medium. Copyright

7-Nitropyrido[1,2-a]benzimidazole and 8-nitropyrido[1,2-a]benzimidazole undergo cleavage-recyclization under the action of an excess of dimethyl acetylenedicarboxylate.

In the presence of a Pd(0) precatalyst, Pd2(bq) 2(nbe)2 or Pd2(dba)3, 1,6-enyne esters were heated in refluxing benzene to give cyclodimers as single regioisomers. On the other hand, the combination of the Pd(0) precatalyst and triphenyl phosphite gave rise to various cycloisomerization products depending on the substitution pattern of the enyne esters. Six-membered ring cycloisomerization products were predominantly obtained from enyne esters bearing methallyl or 2-phenyl-2-propenyl moieties, while other enyne esters afforded normal five-membered ring cycloisomerization products. Intramolecular [2 + 2 + 2] cyclocotrimerization of enediyne esters also proceeded in the presence of the Pd(0) precatalyst and triphenylphosphine to give fused cyclohexadienes.

(Matrix presented) Highly selective cross [2 + 2 + 2] cycloaddition of two different monoynes is achieved by using a catalytic amount of [Ir(cod)Cl] 2 and ligand. The ligand had a considerable effect on the reaction. When 1,2-bis(diphenylphosph

Rhodium η5-complexes bearing an indenyl-type fullerene ligand, Rh[C60(PhCH2)2Ph](cod) (2), Rh[C60(PhCH2)2Ph](nbd) (3) and Rh(C70Ph3)(cod) (4), have been synthesized from the corresponding fullerene tri-adducts in 93-96% yields. X-ray crystallographic analysis of 4 indicated that the structure of 4 is similar to that of Rh(Ind)(cod). The rhodium complex 2 catalyzes alkyne trimerization reactions and hydroboration reactions.

Amphiphilic resin-supported rhodium-phosphine complexes were prepared on polystyrene-poly(ethylene glycol) graft co-polymer (1% DVB cross-linked) beads. The immobilized rhodium complexes exhibited high catalytic activity in water to promote hydroformylation of 1-alkenes, [2+2+2] cyclotrimerization of internal alkynes forming benzene rings, and 1,4-addition of arylboronic acids.

Three new molybdenum(0) complexes, [Mo(CO)3(Hpz)3] (1), [Mo(CO)2(Hpz)2(DMAD)2] (2), (DMAD = dimethyl acetylenedicarboxylate) and [Mo(CO)3(1-Me-imidazole)3] (3) were synthesized and characterized. Their activity and selectivity in alkyne cyclotrimerization and co-trimerization reactions was investigated. The molecular structures of 1 and 2 have been determined by unconventional powder and standard single-crystal diffraction methods, respectively. 1 consists of a pseudo-octahedral complex of C3 symmetry, with the ligands in fac disposition; complex 2, of idealized C2 symmetry, is obtained by substitution of one CO and one pyrazole in 1 by two DMAD ligands, and shows the rare trans configuration of π-bound acetylenic moieties.

A comparative mechanistic study of the nickel(0)-catalyzed homo-oligomerization and co-oligomerization of alkynes and of nitriles has been undertaken, with diphenylacetylene and benzonitrile, towards an array of nickel(0) reagents, such as finely divided nickel, (COD)2Ni, (Bpy)(COD)Ni, (Et3P)4Ni, (Bpy)(PhC≡CPh)Ni and (COD)2Ni-MeAlCl2 combinations in donor (THF) and nondonor (PhMe or neat substrate) solvents. Special attention has been given to the detailed molecular structures of the initial 1:1 adducts, (Bpy)(PhC≡CPh)Ni, (Ph3P)3(PhC≡CPh)Ni and [(Ph3P)(PhC≡N)Ni]4 by a consideration of XRD and IR data. Data from the single crystal XRD analysis of (Bpy)(PhC≡CPh)Ni, reported here for the first time, are shown to be in excellent accord with the presence of a 2,3-diphenylnickelacyclopropene ring for the (PhC≡CPh)Ni moiety with almost coplanar chelating coordination of the bipyridyl ligand, rather than with the presence of simple "side-on" coordination of the alkyne with the metal center. A parallel analysis of XRD and IR data for the two benzonitrile-nickel(0) complexes, which were drawn from previous publications, has concluded that the nickel in (Ph3P)3(PhC≡N)Ni is coordinated in an "end-on" fashion and the nickel centers in [(Ph3P)(PhC≡N)Ni]4 are coordinated as bridges between nitrile units in both an "end-on" and "side-on" manner. The stereochemistry of the acid hydrolysis of the nickelacyclopropene complex to (E)- or (Z)-alkene was shown to depend on the structure of the cleaving acid; parallel hydrolysis of nitrile-nickel complexes has shown that "end- on" complexes regenerate the nitrile, while "side-on" complexes lead to the aldehyde. In homo-oligomerization of diphenylacetylene or other alkyne the clean cyclotrimerization to the benzene derivative was shown to proceed by way of a nickelacyclopentadiene intermediate, as was evident by chemical trapping. The homo-oligomerization of benzonitrile by nickel(0) was found not to lead to 2,4,6-triphenyl-1,3,5-triazine, as claimed in the literature, but rather solely to benzyl phenyl ketone, the dimeric hydrolysis product. The attempted co-oligomerization of diphenylacetylene and benzonitrile with ordinary nickel(0) complexes led only to the homocyclotrimer of the alkyne. Only when the alkyne was prebonded to the nickel, as in (Bpy)(PhC≡N)Ni, could significant amounts of a codimerization product with the nitrile be observed. The origin of the triazine, claimed in a previous report to form from benzonitrile and Raney nickel, has been traced to the presence of adventitious moisture and air. Other unexpected products formed from nickel(0) complexes and benzonitrile have been shown to arise from oxidative addition reactions of nickel(0) with various σ C-E bonds.

The reactivity of mono-substituted HCCR (R=Ph, a; CH2OH, b; CH2CH2CH2CH3, c) and di-substituted RCCR (R=CH2CH3, d; CO2CH3, e; Ph, f) acetylenes was studied in supercritical carbon dioxide (scCO2) using the easily available complex CpCo(CO)2 as catalyst. The reaction of phenylacetylene produced a mixture of the isomeric cyclotrimers 1,3,5- (2a) and 1,2,4-triphenylbenzene (2a′), in a 1:5 ratio, and traces of cobaltcyclopentadienone complexes CpCo(η4-C4H2[Ph]2CO) (6a, mixture of isomers). The possible product formed by the incorporation of CO2 to alkynes, i.e. diphenylpyrone (7a) was not observed. The reaction of the cobaltacyclopentadiene complex CpCo(1.4-σ-C4[Ph]4)(PPh)3 (8f), in scCO2, was performed. No insertion of CO2 into the Co-C σ-bond to form tetraphenylpyrone (7f) by reductive elimination was observed, instead the cobaltcyclobutadiene complex CpCo(η4-C4[Ph]4) (9f) was formed. In the reactions with other alkynes, lower yields were obtained in general, except in the cyclotrimerisation of the highly activated alkyne, propargyl alcohol (b). Reaction of the non-activated alkynes, 1-hexyne (c) and 3-hexyne (d), produced complex mixtures of cobalt complexes in low yield in which the alkyne was coordinated to cobalt. Finally, the highly hindered diphenylacetylene (f) gave a mixture of the known complexes CpCo(η4-C4[Ph]4) (9f) and CpCo(η4-C4[Ph]4CO) (6f) in agreement with the results observed in conventional organic solvents.

The catalytic dimerization and cyclotrimerization of phenylacetylene, ethyl propiolate, and dimethyl acetylenedicarboxylate were studied by using the metal complexes [Co(PPh3)3Cl] (1), [Co(PPh3)2(CO)2

Cationic Rh(I) complex [Rh(binap)(MeOH)2]ClO4 catalyzes reductive dimerization of dialkyl acetylenedicarboxylates 1 to give 1,2,3,4-tetrakis(alkoxycarbonyl)-1,3-butadienes 2 in methanol selectively.

A nickel(0)-catalyzed asymmetric [2+2+2] cocyclization has been realized for the first time. That involves conceptually new enantiotopic group selective formation of the nickelacyclopentadiene (18) and produces the isoindoline (26a) (73percent ee, 78perce