Showing papers on "Norbornene published in 2015"
TL;DR: The Catellani reaction--a palladium-catalysed C-H functionalization reaction mediated by norbornene--was first reported in 1997 and dramatic progress has been made in the past five years, including applications in natural products synthesis.
Abstract: The Catellani reaction--a palladium-catalysed C-H functionalization reaction mediated by norbornene--was first reported in 1997. The capacity to functionalize both the ortho and ipso positions of aryl halides in a single transformation held great appeal. We reported an annulative Catellani reaction in 2000. Since then, our two groups have explored the synthetic utility of this reaction and dramatic progress has been made by a number of groups in the past five years. Whereas the original Catellani reaction uses Pd(0) catalysts, recent studies have shown that Pd(II) catalysts can be used in combination with norbornene to effect (1) direct 2-alkylation of indoles and pyrroles and (2) selective meta-C-H functionalization of arenes bearing commonly used ortho-directing groups, thereby opening new avenues for future research. We describe the most recent developments concerning the Pd-catalysed norbornene-mediated C-H functionalization of arenes, including applications in natural products synthesis. We outline challenges and future opportunities.
358 citations
TL;DR: A highly meta-selective C-H arylation using simple tertiary amines as the directing group takes advantage of Pd/norbornene catalysis, offering a distinct strategy to control the site selectivity.
Abstract: Herein we report a highly meta-selective C–H arylation using simple tertiary amines as the directing group. This method takes advantage of Pd/norbornene catalysis, offering a distinct strategy to control the site selectivity. The reaction was promoted by commercially available AsPh3 as the ligand and a unique “acetate cocktail”. Aryl iodides with an ortho electron-withdrawing group were employed as the coupling partner. A wide range of functional groups, including some heteroarenes, are tolerated under the reaction conditions. In addition, the amine directing group can be easily installed and transformed to other common versatile functional groups. We expect this C–H functionalization mode to have broad implications for developing other meta-selective transformations beyond this work.
316 citations
TL;DR: 2-Carbomethoxynorbornene is identified as a more effective transient mediator to promote a Pd(II)-catalyzed meta-C(sp(2))-H alkylation of amides with various alkyl iodides as well as arylation with previously incompatible aryl iodide.
Abstract: 2-Carbomethoxynorbornene is identified as a more effective transient mediator to promote a Pd(II)-catalyzed meta-C(sp2)–H alkylation of amides with various alkyl iodides as well as arylation with previously incompatible aryl iodides. The use of a tailor-made quinoline ligand is also crucial for this reaction to proceed.
240 citations
TL;DR: It was found that vinyl ether oxidation could be accomplished under mild conditions using an organic photoredox mediator, which led to high yields of polymer and generally good correlation between M(n) values and initial monomer to catalyst loadings.
Abstract: We have developed a method to achieve ring-opening metathesis polymerization (ROMP) mediated by oxidation of organic initiators in the absence of any transition metals. Radical cations, generated via one-electron oxidation of vinyl ethers, were found to react with norbornene to give polymeric species with microstructures essentially identical to those traditionally obtained via metal-mediated ROMP. We found that vinyl ether oxidation could be accomplished under mild conditions using an organic photoredox mediator. This led to high yields of polymer and generally good correlation between Mn values and initial monomer to catalyst loadings. Moreover, temporal control over reinitiation of polymer growth was achieved during on/off cycles of light exposure. This method demonstrates the first metal-free method for controlled ROMP.
162 citations
TL;DR: A palladium/norbornene-catalyzed ortho-arene acylation of aryl iodides by a Catellani-type C-H functionalization is reported, enabled by isopropyl carbonate anhydrides, which serve as both an acyl cation equivalent and a hydride source.
Abstract: Reported herein is a palladium/norbornene-catalyzed ortho-arene acylation of aryl iodides by a Catellani-type C-H functionalization. This transformation is enabled by isopropyl carbonate anhydrides, which serve as both an acyl cation equivalent and a hydride source.
141 citations
TL;DR: The facile and reversible interconversion between neutral and oxidized forms of palladium complexes containing ferrocene-bridged phosphine sulfonate ligands was demonstrated and provides a new strategy to control the olefin polymerization process.
Abstract: The facile and reversible interconversion between neutral and oxidized forms of palladium complexes containing ferrocene-bridged phosphine sulfonate ligands was demonstrated. The activity of these palladium complexes could be controlled using redox reagents during ethylene homopolymerization, ethylene/methyl acrylate copolymerization, and norbornene oligomerization. Specifically in norbornene oligomerization, the neutral complexes were not active at all whereas the oxidized counterparts showed appreciable activity. In situ switching between the neutral and oxidized forms resulted in an interesting “off” and “on” behavior in norbornene oligomerization. This work provides a new strategy to control the olefin polymerization process.
119 citations
TL;DR: A series of phosphine-sulfonate nickel and palladium complexes were synthesized and characterized in this article, where the binding of B(C6F5)3 to a sulfonate oxygen was observed.
80 citations
TL;DR: In this article, a facile strategy has been demonstrated for the selective synthesis of highly stereoregular polyesters with cis-2,3-(exo, exo) or trans- 2,3(exo-endo, endo) repeating units by the organocatalysts mediated alternating copolymerization of cyclohexene oxide and norbornene anhydride (NA) stereoisomers.
Abstract: A facile strategy has been demonstrated for the selective synthesis of highly stereoregular polyesters with cis-2,3-(exo, exo) or trans-2,3-(exo, endo) repeating units by the organocatalysts mediated alternating copolymerization of cyclohexene oxide and norbornene anhydride (NA) stereoisomers. The geometrical structure of polyester can be tuned simply by modulating the type of NA isomers (endo- or exo-NA), monomer feed ratio, and reaction temperature. The cis- (>99%) and trans-polyesters (>99%) exhibit high glass transition temperature up to 129.8 and 115.9 °C, respectively. The resulting polyesters provide a versatile platform to incorporate various functional groups through the robust thiol–ene reaction of the pendant norbornenyl groups.
80 citations
TL;DR: Norbornene is employed as a transient mediator to achieve meta-selective C—H activation with a simple and common ortho-directing group.
Abstract: Norbornene is employed as a transient mediator to achieve meta-selective C—H activation with a simple and common ortho-directing group.
75 citations
TL;DR: In this paper, a ring-opening polymerization of norbornene functionalized with redox-active anthraquinone (AQ) pendants was presented, yielding a high-molecular-weight and processable polynorbornene with large redox capacity.
Abstract: An excellent functional group tolerance of ruthenium complex catalysts for olefin metathesis gave rise to ring-opening polymerization of norbornene functionalized with redox-active anthraquinone (AQ) pendants, yielding a high-molecular-weight and processable polynorbornene with large redox capacity. A thin layer of the polymer cast on current collectors showed reversible redox reaction at −0.85 V vs Ag/AgCl when immersed in basic aqueous electrolyte solutions. Good cycle performance was observed with a capacity comparable to the formula weight-based theoretical density of 212 mAh/g, which was the largest among those for the previously reported redox-active polynorbornenes. This suggested that all of the AQ units in the layer were redox-active, that electroneutralization was accomplished by successive compensation of counterions throughout the layer, and that the mechanical strength of the polymer layer prevented dissolution or exfoliation from the current collector surface. A robust polymer–air secondary ...
71 citations
TL;DR: Three-component couplings were achieved from common aryl halide, alkyl halides, and heteroarenes under palladium and norbornene co-catalysis with the assistance of palladium catalysts.
Abstract: We report an efficient alkynylation reaction of aryl iodides with simultaneous ortho-alkylaton of aryl rings. The reaction between three simple reagents—aryl halides, alkynes, and alkyl halides—formed aryl–alkynyl bonds carrying hindered aryl rings in one step. The reaction proceeded via a Catellani-type pathway in the presence of norbornene. From a synthetic perspective, this reaction allows quick access toward many 1,2,3-substituted arenes and multiply substituted benzofurans, after manipulation of alkyne groups. These compounds are difficult to synthesize otherwise.
TL;DR: Migratory insertion of alkenes into gold-carbon bonds, a fundamental yet unprecedented organometallic transformation, has been investigated from a discrete (P,C) cyclometalated gold(III) dimethyl complex.
Abstract: Migratory insertion of alkenes into gold–carbon bonds, a fundamental yet unprecedented organometallic transformation, has been investigated from a discrete (P,C) cyclometalated gold(III) dimethyl complex. Methide abstraction by B(C6F5)3 is shown to generate a highly reactive cationic AuIII complex that evolves spontaneously by C6F5 transfer from boron. In the presence of norbornene, migratory insertion into the AuC bond proceeds readily. The resulting norbornyl complex is efficiently trapped with pyridines or chloride to give stable four-coordinate adducts.
TL;DR: In this article, the structure of synthesized monomers has been confirmed by 1 H nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infrared spectrography (FT-IR) and differential scanning calorimetry (DSC).
TL;DR: Both the activity and the selectivity increased upon addition of PMe3, even at 50 °C, and the ROMP by 2 proceeded in a living manner, affording ultrahigh molecular weight polymers.
Abstract: (Arylimido)vanadium(V)–alkylidene complexes, V(CHSiMe3)(N-2,6-X2C6H3)(OC6F5)(PMe3)2 [X = Me (2), Cl (4)], exhibited remarkable catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene, and the ROMP by 2 proceeded in a living manner, affording ultrahigh molecular weight polymers. Cis-specific ROMP was achieved with the alkoxo analogues, V(CHSiMe3)(N-2,6-X2C6H3)[OC(CH3)(CF3)2]-(PMe3)2 [X = Me (5), Cl (6)]. Both the activity and the selectivity increased upon addition of PMe3, even at 50 °C.
TL;DR: The peroxometalate-based polymer immobilized ionic liquid phase catalyst [PO4{WO(O2)2}4]@PIILP has been prepared by anion exchange of ring opening metathesis-derived pyrrolidiniumdecorated norbornene/cyclooctene copolymer and shown to be a remarkably efficient system for the selective oxidation of sulfides under mild conditions as discussed by the authors.
TL;DR: In this paper, the synthesis of >98% cis,isotactic and cis,syndiotactic polynorbornene (poly(NBE)) and poly(endo,anti-tetracyclodecene) (Poly(TCD)) was reported, using Mo-based biphenolate imido alkylidene initiators.
Abstract: We report the synthesis of >98% cis,isotactic and cis,syndiotactic polynorbornene (poly(NBE)) and poly(endo,anti-tetracyclododecene) (poly(TCD)). Cis,isotactic poly(NBE) and poly(TCD) were prepared employing Mo-based biphenolate imido alkylidene initiators, Mo(NR)(CHCMe2Ph)(Biphen) (Biphen = e.g., 3,3′-(t-Bu)2-5,5′-6,6′-(CH3)4-1,1′-biphenyl-2,2′-diolate), while cis,syndiotactic poly(NBE) and poly(TCD) were prepared employing W-based imido or oxo monoaryloxide pyrrolide (MAP) initiators, W(X)(CHR′)(Pyrrolide)(OTer) (X = NR or O; OTer = a 2,6-terphenoxide). Addition of 1-hexene or coordinating solvents such as THF do not decrease the stereospecificity of the polymerization. Cis,iso and cis,syndio dyads can be distinguished through examination of 1H and 13C NMR spectra of the two polymers in a mixture. The polymers were hydrogenated to give isotactic and syndiotactic H-poly(NBE) and H-poly(TCD).
TL;DR: Aliphatic terminal alkenes react with pinacolborane at ambient temperature to afford dehydrogenative borylation compounds as the major product when iPr-Foxap is used as the ligand with cationic rhodium(I) in the presence of norbornene.
Abstract: Aliphatic terminal alkenes react with pinacolborane at ambient temperature to afford dehydrogenative borylation compounds as the major product when iPr-Foxap is used as the ligand with cationic rhodium(I) in the presence of norbornene, which acts as the sacrificial hydrogen acceptor. The reaction is applied to the one-pot syntheses of aldehydes and homoallylic alcohols from aliphatic terminal alkenes.
TL;DR: In all complexes, the FcPPAl ligand is coordinated through both phosphines and the alane, and the hydride and carbonyl complexes feature unusual multicenter bonding involving platinum, aluminum, and a hydrides or carbonyL ligand.
Abstract: An aryldimethylalane-appended analogue of 1,1'-bis(diphenylphosphino)ferrocene, FcPPAl, was prepared, and reaction with [Pt(nb)3 ] (nb=norbornene) afforded [Pt(η(2) -nb)(FcPPAl)] (1). Heating a solution of 1 to 80 °C resulted in crystallization of [{Pt(FcPPAl)}2 ] (2), whereas treatment of 1 with C2 H4 , C2 Ph2 , H2 , or CO provided [PtL(FcPPAl)] [L=C2 H4 (3), C2 Ph2 (4)], [PtH2 (FcPPAl)] (5), and [Pt(CO)(FcPPAl)] (6). In all complexes, the FcPPAl ligand is coordinated through both phosphines and the alane. Whereas 2 adopts a T-shaped geometry at platinum, 3-5 are square-pyramidal, and 6 is distorted square-planar. The hydride and carbonyl complexes feature unusual multicenter bonding involving platinum, aluminum, and a hydride or carbonyl ligand.
TL;DR: Under ambient conditions, a [4 + 2] cycloaddition reaction of 1,3,2,5-diazadiborinine 1 with ethylene afforded a bicyclo[ 2.2.2] derivative 2, which was structurally characterized.
Abstract: Under ambient conditions, a [4 + 2] cycloaddition reaction of 1,3,2,5-diazadiborinine 1 with ethylene afforded a bicyclo[2.2.2] derivative 2, which was structurally characterized. The cyclization process was found to be reversible, and thus retro-[4 + 2] cycloaddition reproduced 1 quantitatively, concomitant with the release of ethylene. Compound 1 reacted regio-selectively and stereo-selectively with styrene derivatives and norbornene, respectively, and these processes were found to be reversible too. Computational studies determined the reaction pathways which were consistent with the regio-selectivity observed in the reaction of styrene, and the reaction was suggested to be essentially concerted but highly asynchronous.
TL;DR: An air-stable phenylethynyl Pd(II) complex containing a polymerizable norbornene unit was designed and synthesized in this article, which can initiate the living/controlled polymerization of phenyl isocyanide.
Abstract: An air-stable phenylethynyl Pd(II) complex containing a polymerizable norbornene unit was designed and synthesized. Such a Pd(II) complex can initiate the living/controlled polymerization of phenyl isocyanide, giving stereoregular poly(phenyl isocyanide)s in high yields with controlled molecular weights and narrow molecular weight distributions. The norbornene unit on the Pd(II) complex can undergo ring-opening metathesis polymerization (ROMP) with Grubbs’ second-generation catalyst, affording polynorbornene bearing Pd(II) complex pendants under a living/controlled manner. Interestingly, the Pd(II) complex pendants on the isolated polynorbornene are active enough to initiate the living/controlled polymerization of phenyl isocyanides, yielding well-defined brush-like copolymers with polynorbornene backbone and helical poly(phenyl isocyanide) as side chains. 31P NMR analyses indicate almost all the Pd(II) units on the polynorbornene participated in the polymerization, and the grafting density of the brush c...
TL;DR: In this paper, the vinyl addition polymerization of substituted norbornene (NB) monomers, via (t-Bu3P)PdMeCl activated by [Li(OEt2)2.5]B(C6F5)4, is investigated.
Abstract: The vinyl addition polymerization of substituted norbornene (NB) monomers, via (t-Bu3P)PdMeCl activated by [Li(OEt2)2.5]B(C6F5)4, is investigated. NB monomers bearing alkyl, aryl, fluoroaryl, and even hexafluoroisopropanol substituents yield polymers exhibiting monomodal and narrow molecular weight distributions, with molecular weight controlled by reaction time and monomer to initiator ratio, demonstrating the living nature of these polymerizations. These polymers are soluble in common organic solvents and possess excellent thermal stability. Block copolymers are also prepared via sequential monomer addition; these are the first examples of well-defined block copolymers of substituted NB monomers enchained by vinyl addition polymerization.
TL;DR: The first palladium-catalyzed dearomative cyclization via a modified Catellani-type C-H functionalization has been realized and led to a series of spiroindolenine derivatives bearing an all-carbon quaternary spirocenter from simple aryl halides and substituted indoles.
TL;DR: In this article, a cross-metathesis of polynorbornene with polyoctenamer was used to synthesize copolymers of norbornene and cyclooctene.
Abstract: Copolymers of norbornene and cyclooctene were synthesized for the first time by the cross-metathesis of polynorbornene with polyoctenamer. This strategy made it possible to use the 1st generation Grubbs catalyst, which exhibits low activity toward copolymerization of those monomers. Statistical multiblock copolymers with average block lengths varying from 200 to 2 units were obtained.
TL;DR: In this article, a general method for the incorporation of secondary alkyl iodides in a palladium-catalyzed multicomponent domino reaction was reported, with the relatively inexpensive Pd(OAc)2 as the catalyst and norbornene as a mediator.
Abstract: A general method for the incorporation of secondary alkyl iodides in a palladium-catalyzed multicomponent domino reaction is reported. With the relatively inexpensive Pd(OAc)2 as the catalyst and norbornene as a mediator, a variety of 1,2,3-trisubstituted aromatic compounds were synthesized. The reaction was shown to be scalable, producing excellent isolated yields on up to 5 mmol scale. Chiral alkyl iodides were also incorporated without any loss of stereochemical information. The developed method offers an expedient and mild C–H functionalization strategy for the synthesis of sterically congested aromatic compounds in a one-pot process.
TL;DR: This work presents a two‐step labeling protocol for the site‐specific labeling of proteins based on attachment of a highly stable norbornene derivative to a specific peptide sequence by using a mutant of the enzyme lipoic acid ligase A (LplAW37V), followed by the covalent attachment of tetrazine‐modified fluorophores to the norbornenes moiety through the bio‐orthogonal DAinv .
Abstract: Inverse-electron-demand Diels-Alder cycloaddition (DAinv ) between strained alkenes and tetrazines is a highly bio-orthogonal reaction that has been applied in the specific labeling of biomolecules. In this work we present a two-step labeling protocol for the site-specific labeling of proteins based on attachment of a highly stable norbornene derivative to a specific peptide sequence by using a mutant of the enzyme lipoic acid ligase A (LplA(W37V) ), followed by the covalent attachment of tetrazine-modified fluorophores to the norbornene moiety through the bio-orthogonal DAinv . We investigated 15 different norbornene derivatives for their selective enzymatic attachment to a 13-residue lipoic acid acceptor peptide (LAP) by using a standardized HPLC protocol. Finally, we used this two-step labeling strategy to label proteins in cell lysates in a site-specific manner and performed cell-surface labeling on living cells.
TL;DR: A family of block and random copolymers of norbornene derivatives bearing cholic acid and oligo(ethylene glycol) pendants prepared in the presence of Grubbs' catalyst exhibited a pH-triggered release behavior and may have promise for use as therapeutic nanocarriers in drug delivery systems.
Abstract: A family of block and random copolymers of norbornene derivatives bearing cholic acid and oligo(ethylene glycol) pendants were prepared in the presence of Grubbs’ catalyst. The phase transition temperature of the copolymers in aqueous solutions may be tuned by the variation of comonomer ratios and pH values. Both types of copolymers formed micellar nanostructures with a hydrophilic poly(ethylene glycol) shell and a hydrophobic core containing cholic acid residues. The micellar size increased gradually with increasing pH due to the deprotonation of the carboxylic acid groups. These micelles were capable of encapsulating hydrophobic compounds such as Nile Red (NR). A higher hydrophobicity/hydrophilicity ratio in both copolymers resulted in a higher loading capacity for NR. With similar molecular weights and monomer compositions, the block copolymers showed a higher loading capacity for NR than the random copolymers. The NR-loaded micelles exhibited a pH-triggered release behavior. At pH 7.4 within 96 h, the...
TL;DR: Engineered single-electron transfer reactions of these redox-robust nanomaterial precursors appear to be a new way to control their formation, size, and environment in a supramolecular way.
Abstract: We report the first pentamethylferrocene (PMF) polymers and the redox chemistry of their robust polycationic pentamethylferricenium (PMFium) analogues. The PMF polymers were synthesized by ring-opening metathesis polymerization (ROMP) of a PMF-containing norbornene derivative by using the third-generation Grubbs ruthenium metathesis catalyst. Cyclic voltammetry studies allowed us to determine confidently the number of monomer units in the polymers through the Bard-Anson method. Stoichiometric oxidation by using ferricenium hexafluorophosphate quantitatively and instantaneously provided fully stable (even in aerobic solutions) blue d(5) Fe(III) metallopolymers. Alternatively, oxidation of the PMF-containing polymers was conducted by reactions with Ag(I) or Au(III) , to give PMFium polymer-embedded Ag and Au nanoparticles (NPs). In the presence of I2 , oxidation by using Ag(I) gave polymer-embedded Ag/AgI NPs and AgNPs at the surface of AgI NPs. Oxidation by using Au(III) also produced an Au(I) intermediate that was trapped and characterized. Engineered single-electron transfer reactions of these redox-robust nanomaterial precursors appear to be a new way to control their formation, size, and environment in a supramolecular way.
TL;DR: Aryloxo-modified vanadium(V) dichloride complexes containing a dichloro- or difluoro-phenylimido ligand of the type, V(N-2,6-X2C6H3)Cl2(O-6-R2C 6H3), showed remarkable catalytic activity in ethylene polymerisation and the copolymerisation with norbornene (NBE) in the presence of Et2AlCl.
Abstract: Aryloxo-modified vanadium(V) dichloride complexes containing a dichloro- or difluoro-phenylimido ligand of the type, V(N-2,6-X2C6H3)Cl2(O-2,6-R2C6H3) [X = Cl (1), F (2); R = Me (a), F (b)], showed remarkable catalytic activity in ethylene polymerisation and the copolymerisation with norbornene (NBE) in the presence of Et2AlCl; the activities were higher than that of V(N-2,6-Me2C6H3)Cl2(O-2,6-Me2C6H3) reported previously. Complex 1a is a suitable catalyst precursor in terms of not only the activity, but also synthesis of high molecular weight copolymers with both unimodal molecular weight distributions and uniform compositions.
TL;DR: A single-crystal X-ray diffraction study reveals that, in the solid state, the P-carborane bond of the ligand is rapidly rotating at temperatures as low as -90 °C, which demonstrates the carborane substituent's weak coordinative ability even though this anion is covalently linked to the phosphine ligand.
Abstract: A zwitterionic palladium complex of a phosphine bearing a perchlorinated carba-closo-dodecaborate anion as a ligand substituent is reported. A single-crystal X-ray diffraction study reveals that, in the solid state, one of the chlorides of the carborane cage occupies a coordination site of the square-planar complex. However, in solution, the P–carborane bond of the ligand is rapidly rotating at temperatures as low as −90 °C, which demonstrates the carborane substituent’s weak coordinative ability even though this anion is covalently linked to the phosphine ligand. The complex is thermally stable and catalyzes the vinyl addition polymerization of norbornene.
TL;DR: In this article, an efficient method to synthesize o-hydroxyaryl-substituted imidazoles (2-OH-3-R-5-tBuC6H2)(C3H3N2) was developed through copper-catalyzed C-N bond formation.