Cyclotrimerization Products Research Articles

Carbonylation of Boranes – A Computational Study

AbstractThe classical simple picture of stepwise B‐to‐C migratory insertion of all three alkyl groups in the carbonylation reaction of trialkyl boranes with CO was shown not to be correct, except for the first alkyl group shift affording an acyl borane. The second and third direct alkyl shifts turned out to be kinetically hampered due to the non‐activated character of the B−C bond in electron‐poor B atoms. The latter can only be achieved by either the autocatalytic action of the final alkyl boron oxide or by formation of dimeric species with weakened B‐alkyl bonds at borate centres. Both thermodynamic and several NICS‐related parameters pointed to scarce, even “negative”, aromatic character for boroxines, the final cyclotrimerization products of alkyl‐boron oxides.

Cyclotrimerization Approach to Symmetric [9]Helical Indenofluorenes: Diverting Cyclization Pathways.

Catalytic cyclotrimerization routes to symmetrical [9]helical indenofluorene were explored by using different transition-metal complexes and thermal conditions. Depending on the reaction conditions, the cyclotrimerizations were accompanied by dehydro-Diels-Alder reaction giving rise to another type of aromatic compounds. Structures of both symmetrical [9]helical cyclotrimerization product as well as the dehydro-Diels-Alder product were confirmed by single-crystal X-ray diffraction analyses. Limits of enantioselective cyclotrimerization were assessed as well. DFT calculations shed light on the reaction course and the origin of diminished enantioselectivity.

Pyridinic Nitrogen Modification for Selective Acetylenic Homocoupling on Au(111)

On-surface acetylenic homocoupling has been proposed to construct carbon nanostructures featuring sp hybridization. However, the efficiency of linear acetylenic coupling is far from satisfactory, often resulting in undesired enyne products or cyclotrimerization products due to the lack of strategies to enhance chemical selectivity. Herein, we inspect the acetylenic homocoupling reaction of polarized terminal alkynes (TAs) on Au(111) with bond-resolved scanning probe microscopy. The replacement of benzene with pyridine moieties significantly prohibits the cyclotrimerization pathway and facilitates the linear coupling to produce well-aligned N-doped graphdiyne nanowires. Combined with density functional theory calculations, we reveal that the pyridinic nitrogen modification substantially differentiates the coupling motifs at the initial C-C coupling stage (head-to-head vs head-to-tail), which is decisive for the preference of linear coupling over cyclotrimerization.

Catalytic approach to unsymmetrical [7]-helical indenofluorenes: Cyclotrimerization vs. dehydro-Diels-Alder reaction pathways

Synthesis of unsymmetrical [7]-helical compounds possessing the dispiro[2,1-c]indenofluorene motif was achieved for the first time in good yields. The crucial step of the whole reaction sequence was catalytic intramolecular [2 + 2 + 2] cycloaddition of triynediols by using various transition metal compounds (Co, Ni, etc.). The cyclotrimerizations were accompanied by dehydro-Diels-Alder reaction giving rise to other types of aromatic compounds depending on the respective reaction conditions. Limits of enantioselective cyclotrimerization were assessed. The subsequent transformations of the cyclotrimerization products provided the respective dispiroindenofluorenes. Structures of both unsymmetrical [7]helical cyclotrimerization products as well as three dehydro-Diels-Alder products were unequivocally confirmed by single-crystal X-ray diffraction analyses. Photophysical properties of selected products were determined as well.

Catalytic Cyclotrimerization Pathway for Synthesis of Selaginpulvilins C and D: Scope and Limitations.

A facile and unified approach to the main selaginpulvilin's framework was achieved by catalytic [2 + 2 + 2]-cyclotrimerization of a triyne with monosubtituted alkynes. The reaction proceeded with high "ortho" selectivity by using Wilkinson's catalyst (RhCl(PPh3)3) under ambient conditions with reasonable yields. The scope of the reaction with respect to the alkyne as well as the catalytic system was evaluated. The formal total modular syntheses of selaginpulvilin C and D were accomplished by transformation of the cyclotrimerization's products.

Surface‐Dependent Chemoselectivity in C−C Coupling Reactions

AbstractSurface‐confined covalent coupling reactions of the linear compound 4‐(but‐3‐en‐1‐ynyl)‐4′‐ethynyl‐1,1′‐biphenyl (1), which contains one alkyne and one enyne group on opposing ends, have been investigated using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The reactions show a surface‐dependent chemoselectivity: on Au(111), compound 1 preferentially yields cyclotrimerization products, while on Cu(111), a selective coupling between the enyne and alkyne groups is observed. Linear, V‐shaped string formations combined with Y‐shaped bifurcation motifs result in a random reticulation on the entire surface. DFT calculations show that the C−H⋅⋅⋅πδ− transition state of the reaction between the deprotonated alkyne group and a nearby H‐donor of the alkene group plays a key role in the mechanism and high chemoselectivity. This study highlights a concept that opens new avenues to the surface‐confined synthesis of covalent carbon‐based sp–sp2 polymers.

Surface-Dependent Chemoselectivity in C-C Coupling Reactions.

Surface-confined covalent coupling reactions of the linear compound 4-(but-3-en-1-ynyl)-4'-ethynyl-1,1'-biphenyl (1), which contains one alkyne and one enyne group on opposing ends, have been investigated using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The reactions show a surface-dependent chemoselectivity: on Au(111), compound 1 preferentially yields cyclotrimerization products, while on Cu(111), a selective coupling between the enyne and alkyne groups is observed. Linear, V-shaped string formations combined with Y-shaped bifurcation motifs result in a random reticulation on the entire surface. DFT calculations show that the C-H⋅⋅⋅πδ- transition state of the reaction between the deprotonated alkyne group and a nearby H-donor of the alkene group plays a key role in the mechanism and high chemoselectivity. This study highlights a concept that opens new avenues to the surface-confined synthesis of covalent carbon-based sp-sp2 polymers.

Effect of solvation of ionic liquid on Brønsted acid‐catalyzed aldol cyclotrimerization of indanones and related cyclic ketones

AbstractAldol cyclotrimerization of 1‐indanone afforded truxene in ionic liquid [BMIM][Tf2N] in the presence of p‐TsOH as a Brønsted acid catalyst. Truxene was easily isolated by filtration, and the ionic liquid containing p‐TsOH could be reused. Cyclic ketones such as 2‐indanone, cyclopentanone, and cyclohexanone successfully gave aldol cyclotrimerization products in ionic liquid. The reaction mechanism for the cyclotrimerization of 1‐indanone was assessed by the DFT calculations with the polarizable continuum model. The reaction involves 3 C─C bond forming steps: the first aldol reaction of 1‐indanone, the second aldol reaction of a dimer, and 6π‐electrocyclization of a trimer, whose transition states were computed to be energetically the highest in the entire reaction sequence. The second aldol reaction is considered to proceed through 2 alternative pathways: a nucleophilic addition of inden‐1‐ol to O‐protonated 2‐(1‐indanylidene)‐1‐indanone and a nucleophilic addition of 2‐(1‐indenyl)inden‐1‐ol to O‐protonated 1‐indanone. The transition state of the latter pathway was estimated to be energetically favored over that of the former by 3 kcal/mol, suggesting that the second aldol condensation proceeds by the latter pathway according to the Curtin‐Hammett principle. Stabilization by aromatization at the final step was confirmed to be the driving force for the reaction. Reaction rates of the first and the second aldol reaction process were enhanced by using a polar ionic liquid, but the electrocyclization was found to remain similar.

Nickel-Catalyzed Facile [2+2+2] Cyclotrimerization of Unactivated Internal Alkynes to Polysubstituted Benzenes.

A catalytic [2+2+2] cyclotrimerization of unactivated internal alkynes providing cyclotrimerization products in excellent yields with high regioselectivity is described. The transformation is accomplished by using a simple catalytic mixture comprising Ni(acac)2 , an imidazolium salt and a Grignard reagent at room temperature or 60 °C for 20 min or 1 h.

Reaction of [TpRh(C2 H4 )2 ] with Dimethyl Acetylenedicarboxylate: Identification of Intermediates of the [2+2+2] Alkyne and Alkyne-Ethylene Cyclo(co)trimerizations.

The reaction between the bis(ethylene) complex [TpRh(C2 H4 )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 TpRh(I) species were prevalent, whereas the presence of trapping agents, like water or acetonitrile, allowed for the stabilization and isolation of octahedral TpRh(III) compounds. 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 effect of tunable modification parameters on the structure and properties of polypropylene with cyclotrimerization surface of isocyanates

ABSTRACTThe cyclotrimerization of methylene diphenyl 4,4‐diisocyanate (MDI) and 3‐isopropenyl‐α,α′‐dimethylbenzene isocyanate (TMI) was applied on the bead/membrane surfaces of a polypropylene (PP)‐bearing isocyanate group to synthesize a protective networked polymer. Chemical structures of these molecules were characterized through attenuated total reflectance–Fourier transform infrared spectroscopy. Results showed that the absorption peak of isocyanate group at 2255 cm−1 became negligible after the reaction was completed. The absorption peaks of the isocyanurate groups appeared simultaneously at 1600 cm−1 and at 1510–1560 cm−1; this result indicated that the grafted isocyanates were almost consumed, thereby forming isocyanurates. Energy X‐ray dispersive spectroscopy revealed that oxygen content increased; indeed, isocyanurate was formed on the PP surface. Pure PP beads, PP‐g‐TMI, and cyclotrimerization products were also subjected to thermal property tests to investigate their corresponding thermal stabilities. Cyclotrimerization could result in the increase in PP‐grafted decomposition temperature, even slightly higher than pure PP. Rheological behavior in oscillatory flow was also evaluated; the storage modulus, loss modulus, and complex viscosity of cyclotrimerization products were higher than those of the PP‐grafted membranes. Surface morphology was further observed through field‐emission scanning electron microscopy and atomic force microscopy. The cyclotrimerization products contained blocks and exhibited a rough surface. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43327.

Star-Shaped Macromolecules with the Core of Hexakis-(fluoren-2-yl)benzene and the Periphery of Pyridine: Synthesis and Application as Solution-Processable Electron-Transport Materials.

Three new star-shaped macromolecules with hexakis(fluoren-2-yl)benzene as the core and pyridine as the periphery (2Py-HFB, 3Py-HFB, and 4Py-HFB) are synthesized and characterized. The synthetic conditions of octacarbonyldicobat-catalyzed cycloaddition reaction for different alkyne precursors are investigated. The coordination interaction between the pyridine ring of alkyne precursor and the cobalt catalyst may result in very low yield of the cyclotrimerization product. However, with the increase of the catalyst loading, the yields of the intermediates of cyclopentadienone are enhanced. Then, the desired cyclotrimerization products can be obtained by the Diels-Alder reactions of cyclopentadienone with acetylene in good yield. These new compounds exhibit good thermal stability and favorable electron affinity. By using the new compounds as electron-transporting materials, all-solution-processed phosphorescent organic light-emitting devices (OLEDs) show good performance with a maximum current efficiency of 5.6 cd A(-1) and maximum external quantum efficiency of 4.68%.

ChemInform Abstract: Palladium Catalyzed [2 + 2 + 1] Cyclotrimerization of Alkynes: Selective Synthesis of Fulvenes.

Abstract This is the first report on the selective synthesis of fulvenes via a [2+2+1] cyclotrimerization of alkynes under catalytic conditions. The reactions of aliphatic terminal alkynes 1a – e in the presence of a palladium catalyst in toluene gave the cyclotrimerization products 2a – e , not easily available through the previously known methods, in good to fair yields.

Competitive intermolecular cyclotrimerization and cyclocarbonylation products in Pauson–Khand reaction

Abstract The catalytic activity of a Co2(CO)8/dppe (C3) solution system is compared with binuclear complexes Co2(CO)6[P(Ph)3]2 (C1) and Co2(CO)6[P(OPh)3]2 (C2). The C3 system, likewise C1 and C2, catalyses the Pauson–Khand (PK) reaction employing strained olefins and does not promote double carbonylation as occurs with C2. Under more drastic reaction conditions, the use of C2 and C3 in presence of less structural strained olefins yields a mixture of products: PK and alkyne cyclotrimerization leading to aromatic compounds. Alkyne cyclotrimerization under these PK reaction conditions appears to be the first example reported. IR studies suggest the formation of an alkynyl–Co2(CO)4-μ2-(Ph)2PCH2CH2P(Ph)2 symmetric complex as the catalytic species active in the system.

Reaction of [Ru 3(CO) 12] with tri(2-furyl)phosphine: Di- and tri-substituted triruthenium and phosphido-bridged diruthenium complexes

Reaction of [Ru 3(CO) 12] with tri(2-furyl)phosphine, P(C 4H 3O) 3, at 40 °C in the presence of a catalytic amount of Na[Ph 2CO] furnishes two triruthenium complexes [Ru 3(CO) 10{P(C 4H 3O) 3} 2] ( 1) and [Ru 3(CO) 9{P(C 4H 3O) 3} 3] ( 2) with the ligand coordinated through the phosphorus atom. Treatment of 1 and 2 with Me 3NO at 40 °C affords the dinuclear phosphido-bridged complexes [Ru 2(CO) 6(μ-η 1,η 2-C 4H 3O){μ-P(C 4H 3O) 2}] ( 3) and [Ru 2(CO) 5(μ-η 1,η 2-C 4H 3O){μ-P(C 4H 3O) 2}{P(C 4H 3O) 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 [Ru 3(CO) 12] with tri(2-furyl)phosphine in refluxing benzene gives, in addition to 3 and 4, low yields of the cyclometallated complex [Ru 3(CO) 9{μ-η 1,η 1-P(C 4H 3O) 2(C 4H 2O)} 2] ( 5). Treatment of 3 with EPh 3 (E = P, As, Sb) at room temperature yields the monosubstituted derivatives [Ru 2(CO) 5(μ-η 1,η 2-C 4H 3O){μ-P(C 4H 3O) 2}(EPh 3)] (E = P, 8; E = As, 9; E = Sb, 10). Similar reactions of 3 with P(C 4H 3O) 3, P(OMe) 3 and Bu t NC yield 4, [Ru 2(CO) 5(μ-η 1,η 2-C 4H 3O){μ-P(C 4H 3O) 2}{P(OMe) 3}] ( 11) and [Ru 2(CO) 5(μ-η 1,η 2-C 4H 3O){μ-P(C 4H 3O) 2}(NCBu t )] ( 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)Ru 2(CO) 6(μ-η 1,η 2-C 4H 3O){μ-P(C 4H 3O) 2}] + ( 6) and [(μ-H)Ru 2(CO) 5(μ-η 1,η 2-C 4H 3O){μ-P(C 4H 3O) 2}{P(C 4H 3O) 3}] + ( 7), respectively, while heating 3 with dimethylacetylenedicarboxylate (DMAD) in refluxing toluene gives the cyclotrimerization product, C 6(CO 2Me) 6.

Iridium-catalyzed addition of methanol to internal alkynes

The 18-crown-6 (18C6) ether adduct of sodium hexachloroiridate [Na(18C6)] 2[IrCl 6]· xH 2O ( 1) was found to catalyze an addition of methanol to a wide variety of internal alkynes RC CR′ (R/R′ = Et/Et, Me/Et, Me/ nPr, Me/ nBu, Me/ tBu, Me/Ph, Et/ nPr, Et/Ph) yielding the corresponding ketals and, due to the presence of water traces, their hydrolysis products (ketones). The regioselectivity of the addition of methanol to unsymmetrically disubstituted internal alkynes is governed by steric and electronic factors, being the highest in the case of pent-2-yne, hex-2-yne and hept-2-yne (80–85%). In the case of MeC CCO 2Me, an alkyne having an electron-withdrawing substituent, the addition was found to be 100% regioselective, with two methoxy groups going to the side away from an ester group. Furthermore, in the analogous addition of methanol to MeO 2CC CCO 2Me, besides the vinyl ethers ( E)/( Z)-MeO 2CC(OMe) CHCO 2Me, a cyclotrimerization product (C 6(CO 2Me) 6) was also observed. A comparison of the catalytic potential of other iridium compounds in the addition of methanol to hex-3-yne revealed that all examined ionic hexachloroiridates ([Na(18C6)] 2[IrCl 6]· xH 2O, Na 2[IrCl 6]·6H 2O, H 2[IrCl 6]·6H 2O, Na 3[IrCl 6]· xH 2O) were catalytically active, whereas [IrCl(CO)(PPh 3) 2] and [(IrCl 2Cp*) 2] were found to be almost inactive (degree of conversion <10%). However, the best results were obtained for the crown ether adduct 1. Moreover, in the addition of CD 3OD to hex-3-yne, [Na(18C6)] 2[IrCl 6]· xH 2O ( 1) was also found to catalyze a H/D exchange of protons in the neighborhood of a keto group or a quaternary carbon of a ketal with a degree of deuteration >97%.

Solid-Supported [2+2+2] Cyclotrimerizations Catalyzed by Rh and Ru

The reaction of polystyrene-supported dipropargylamine 1 with alkyne 2 in the presence of RhCl(PPh3)3 gave the cyclotrimerization product 3. Treatment of 3 with HCl yielded isoindolines 4 in 69-95% yield as HCl salts (eq. 1). Cyclotrimerization of diynes 5 with 2 in the presence of RhCl(PPh3)3 followed by cleavage from the polystyrene support afforded indanes 7 in 60-84% yield (eq. 2). Cyclotrimerization of 8 with 2 in the presence of RuCl(cod)Cp* as catalyst followed by treatment with K2CO3 gave the phthalans 10 in 68-95% yield with good regio­selectivity (eq. 3).

Carbon Dioxide Promoted Palladium‐Catalyzed Cyclotrimerization of Alkynes in Water

In water, CO2 was found to promote the palladium‐catalyzed cyclotrimerization of alkynes. In the presence of PdCl2, CuCl2, and CO2, both aryl and alkylalkynes afforded the corresponding cyclotrimerization products regioselectively in high yields. However, tert‐butylacetylene bearing a bulk group gave a dimerization product.

Novel role of carbon dioxide as a selective agent in palladium‐catalyzed cyclotrimerization of alkynes

AbstractCarbon dioxide was found as a selective agent to promote the palladium‐catalyzed cyclotrimerization of alkynes in water. Both aryl and alkylacetylenes afforded the corresponding cyclotrimerization products regioselectively in high yields using PdCl2, CuCl2, and CO2 as the catalytic system. However, tert‐butylacetylene bearing a bulky group gave a dimerization product. Mechanism of this reaction was also discussed.

The influence of cocatalysts on phenylacetylene oligo- and polymerization

Abstract Titanium bisphenolate complexes [Ti(edbp)Cl 2 ] ( 1 ), [Ti 2 (μ-OEt) 2 (edbp) 2 (OEt) 2 ] ( 2 ) and [Ti 2 (μ-OMe) 2 (edbp) 2 (Me) 2 ] ( 3 ) (edbpH 2 = 2,2′-ethylidenebis(4,6-di- tert -butylphenol) combined with trialkyl aluminium AlR 3 (R = Me, Et, i Bu) activators induce phenylacetylene (PA) oligo- and/or polymerization. It was found that the catalytic activity and products formation depend strongly on the used cocatalyst. The 1 /AlEt 3 catalyst has the highest activity and selectivity (96% conversion; 98% trans -PPA). The PPA has low M n values (2200) and PDI exceeding 1.04. Instead, 1 /Al i Bu 3 produces only cyclotrimers. Polymer formed by 2 /AlEt 3 possesses lower polydispersion index (PDI values 2.5) but high molecular weight ( M n ca. 13 × 10 3 ) and was the mixture of cis and trans stereoisomers of PPA. The compound 3 containing terminal methyl groups was unable to promote PA polymerization in absence of activators, only cyclotrimerization products (10% conversion) were formed.