Showing papers on "Metathesis published in 1999"
TL;DR: These air- and water-tolerant complexes were shown to exhibit an increased ring-closing metathesis activity at elevated temperature when compared to that of the parent complex 2 and the previously developed complex 3.
3,127 citations
TL;DR: A Ru carbene (8, Scheme 2) that contains an internal metal−oxygen chelate is an active metathesis catalyst and is readily obtained by the sequential treatment of Cl2Ru(PPh3)3 with (2-isopropoxyphenyl)diazomethane and PCy3 as mentioned in this paper.
Abstract: A Ru carbene (8, Scheme 2) that contains an internal metal−oxygen chelate is an active metathesis catalyst and is readily obtained by the sequential treatment of Cl2Ru(PPh3)3 with (2-isopropoxyphenyl)diazomethane and PCy3 This Ru-carbene complex offers excellent stability to air and moisture and can be recycled in high yield by silica gel column chromatography The structures of this and related complexes have been unambiguously established by NMR and single-crystal X-ray diffraction studies
878 citations
TL;DR: In this article, an air and water tolerant, imidazolinylidene-substituted ruthenium-based complex has been prepared starting from RuCl2(CHPh)(PCy3)2 and shown to exhibit increased ring-closing metathesis activity at elevated temperature compared to that of the parent complex.
793 citations
TL;DR: Two N-heterocyclic carbene ligands at once may be one too many, at least if you intend to have highly active ruthenium catalysts for olefin metathesis.
Abstract: Two N-heterocyclic carbene ligands at once may be one too many, at least if you intend to have highly active ruthenium catalysts for olefin metathesis. Density functional calculations recommend the replacement of the second carbene ligand in the successful ROMP catalysts 1 by coordinatively more labile ligands as in 2 or 3. In both cases, the catalytic activity is greatly improved.
433 citations
TL;DR: Ruthenium carbene complexes 2-8 bearing one or two imidazolin-2-ylidene ligands are highly active catalysts for all types of ring closing metathesis reactions (RCM) as mentioned in this paper.
368 citations
TL;DR: In this article, the authors studied thermolytic decomposition pathways for several ruthenium carbene-based olefin metathesis catalysts and compared the longevity of these catalysts.
Abstract: Thermolytic decomposition pathways were studied for several ruthenium carbene-based olefin metathesis catalysts. Substituted carbenes were found to decompose through bimolecular pathways while the unsubstituted carbene was found to decomposed unimolecularly. Implications for ring-closing metathesis are discussed, and the longevity of several ruthenium-based catalysts are compared.
333 citations
TL;DR: Trisubstituted alkenes have been prepared for the first time via intermolecular olefin cross-metathesis, using 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene ruthenium alkylidene complexes 3a,b in good yields with moderate E selectivity.
282 citations
TL;DR: In this paper, the ring-closing metathesis (RCM) products of reactions utilizing RuCl2(CHPh)(PCy3)2 (1) as a catalyst were successfully purified of unwanted ruthenium using a water-soluble coordinating phosphine, tris(hydroxymethyl)phosphine, P(CH2OH)3.
276 citations
TL;DR: An overview of the current knowledge about rhenium-based metathesis catalysts, in particular the industrially used Re 2 O 7 /Al 2 O 3 catalyst, is given in this article.
208 citations
TL;DR: The indenylidene−imidazolylidene complexes of ruthenium (IMes)(PR3)Cl2Ru(3-phenylindenylID-1-ene) and (IPr)(PR 3)Cl 2Ru(1-en-ene), and R= Ph, Cy) were prepared and found to be efficient catalyst precursors for ring-closing metathesis.
204 citations
TL;DR: In this paper, a new heterogeneous palladium(II)-based catalyst and its homogeneous analogue and their use for Heck-type, alkyne and amine couplings are described.
Abstract: The preparation of a new heterogeneous palladium(II)-based catalyst and its homogeneous analogue and their use for Heck-type, alkyne and amine couplings are described. The heterogeneous catalytic system is based on a polymer-bound dichloropalladium di(pyrid-2-yl)amide and was prepared via ring-opening metathesis copolymerization of norborn-2-ene-5-(N,N-di(pyrid-2-yl))carbamide with 1,4,4a,5,8,8a-hexahydro-1,4,5,8-exo-endo-dimethanonaphthalene and subsequent loading of the resulting resin with palladium(II) chloride. The heterogeneous catalyst is air, moisture, and temperature stable up to 150 °C and highly active (94−99% yields) in the vinylation of aryl iodides and aryl bromides (Heck-type couplings) with turn-over numbers (TONs) of up to 210000. Even higher TON's (up to 350000) may be achieved in the arylation of alkynes. High yields (≤95%) and TONs (≤24000) may additionally be achieved in the tetrabutylammonium bromide (TBAB) assisted vinylation of aryl chlorides. Moderate yields (<65%) and TONs (<4000...
TL;DR: This study presents a detailed description of a synthetic strategy to obtain catenane architectures through ring-closing metathesis based on phenanthroline-based ligands containing terminal olefinic units that were designed to coordinate in a tetrahedral arrangement around a copper atom.
Abstract: This study presents a detailed description of a synthetic strategy to obtain catenane architectures through ring-closing metathesis. The approach is based on phenanthroline-based ligands containing terminal olefinic units that were designed to coordinate in a tetrahedral arrangement around a copper atom. Treatment of the assembled copper complexes with ruthenium catalyst 1 resulted in [2]catenates in high yields of 88−92%. Demetalation produced the corresponding [2]catenand in nearly quantitative yields. Hydrogenation of the catenates with Crabtree's catalyst and subsequent demetalation yielded fully saturated catenands. The presently described procedure makes [2]catenanes very accessible since the synthetic route consists of six steps (Schemes 2 and 4) from commercially available 1,10-phenanthroline, the overall yield being 51%.
TL;DR: In this article, a strategy for the enantioselective construction of medium-ring cyclic ethers by merging the asymmetric aldol addition of glycolates with a ring-closing metathesis reaction is described.
Abstract: A strategy is described for the enantioselective construction of medium-ring cyclic ethers by merging the asymmetric aldol addition of glycolates with a ring-closing metathesis reaction. Cyclic ethers of seven-, eight-, and nine-membered rings are readily available through a ring-closing metathesis without cyclic conformational constraints, by exploiting the acyclic conformational bias of the gauche effect. A short formal synthesis of the eight-membered ether (+)-laurencin, a red algae metabolite, has been accomplished utilizing the aldol−metathesis combination.
TL;DR: In this article, a new class of chiral Mo-based complexes 2a and 2b, bearing functionalized chiral binol ligands, is disclosed, which are particularly effective in the enantioselective synthesis of five-membered rings by ARCM.
Abstract: A new class of chiral Mo-based complexes 2a and 2b, bearing functionalized chiral binol ligands, is disclosed. Mo complex 2a promotes the asymmetric ring-closing metathesis (ARCM) of various dienes and trienes to afford six-membered carbo- and heterocycles efficiently and in high optical purity. The binol-based chiral Mo catalysts complement the previously reported biphen-based complexes, which are particularly effective in the enantioselective synthesis of five-membered rings by ARCM. Studies regarding catalytic kinetic resolutions and asymmetric desymmetrizations are described. It is possible to obtain optically pure products in high yield from catalytic reactions without the use of solvent (cf. eq 1). The structural attributes of these complexes are detailed on the basis of the data available from an X-ray structure and variable-temperature 1H NMR studies. The results of this investigation indicate the following: (i) The anti-Mo·THF complex exists as a mixture of diastereomers, whereas the syn isomer ...
TL;DR: A trans configuration and phosphane dissociation are not necessarily necessary for catalytic activity in Grubbs-type ruthenium carbene complexes as mentioned in this paper, as shown by the fact that the chelate ligand tBu2PCH2PtBu2 (dtbpm) is an active catalyst for the ring opening metathesis polymerization of norbornene and cyclopentene.
Abstract: Atrans configuration and phosphane dissociation are not necessarily prerequisites for catalytic activity in Grubbs-type ruthenium carbene complexes [(PR3)2Cl2RuCR1R2]. This is shown by the fact that the complex [(η2-dtbpm)Cl2Ru=CH−CHCMe2] (1), in which the chelate ligand tBu2PCH2PtBu2 (dtbpm) enforces a cis geometry and disfavors phosphane dissociation, is an active catalyst for the ring opening metathesis polymerization (ROMP) of norbornene [Eq. (a)] and cyclopentene.
TL;DR: In this article, a ring-closing metathesis (RCM) based approach was used to synthesize tricolorin A (1), tricolorsorin G (2), and jalapinolic acid (58) from the same set of substrates.
Abstract: A highly efficient entry into the resin glycoside family of natural products is outlined which takes advantage of the inherently modular character of ring-closing metathesis (RCM) for the formation of their macrolactone substructures. Starting from only three well accessible sugar building blocks and (6S)-undec-1-en-6-ol (7) (prepared by enantioselective addition of dipentylzinc to hexenal in the presence of a catalyst formed from Ti(OiPr)4 and bis-(R,R)-trifluoromethanesulfonamide (9)), it was possible to achieve total syntheses of tricolorin A (1), tricolorin G (2), and jalapinolic acid (58) as well as the synthesis of the disaccharidic unit 48 which constitutes a common structural motif of all simonin, operculin, tuguajalapin, orizabin, mammoside, quamoclin, and stoloniferin resin glycosides. Furthermore, various analogues of these naturally occurring glycolipids have been obtained in a straightforward manner from the same set of substrates. This highlights the flexibility of the chosen approach and op...
TL;DR: In this article, a 16-electron ruthenium allenylidene complex (PCy3)2Cl2Ru(CCCPh2) (3) with two equiv of PCy3 and 3,3-diphenylpropyn-3-ol was proposed.
TL;DR: The well defined, conveniently accessible and coordinatively unsaturated allenylidene complexes [RuCl2(CC CPh2)(PCy3)2] and [Ru2Cl4(CCCPh2)2) as discussed by the authors are highly effective catalysts for the ambient temperature ring-closure metathesis of α,ω-dienes and dienynes, illustrated by the facile and high yielding formation of variously functionalised 5, 6, 7, 8, 15, 16 and 18 membered mono- and bi-cyclic ring systems.
TL;DR: The first ring-closing metathesis (RCM) reactions on allyl and vinylsulfonamide templates were described in this paper, where the rate of cyclization was sensitive to simple olefin substitution.
TL;DR: Cationic RuII carbene complexes with tBu2 PCH2 PtBu2 (dtbpm) as a chelating ligand, which are accessible by chloride abstraction from neutral precursors, are established as highly efficient ring opening metathesis polymerization catalysts (see scheme).
Abstract: Cationic RuII carbene complexes with tBu2 PCH2 PtBu2 (dtbpm) as a chelating ligand, which are accessible by chloride abstraction from neutral precursors [(κ2 -dtbpm)Cl2 Ru=CHR] with trimethylsilyl triflate, are established as highly efficient ring opening metathesis polymerization catalysts (see scheme). Solv=solvent.
TL;DR: In this article, the acyclic diene metathesis of vegetable oils utilizing Grubbs' ruthenium catalyst (Cy3P)2Cl2Ru = CHPh has been developed.
Abstract: A new process for the acyclic diene metathesis of vegetable oils utilizing Grubbs’ ruthenium catalyst (Cy3P)2Cl2Ru = CHPh has been developed. The higher molecular weight oligomers obtained can be separated from the unreacted oil and the lower molecular weight alkene by-products easily. The reaction proceeds in the absence of solvent, with very low catalyst concentrations (0.1 mole %) under moderate temperatures and low pressures. This process does not require the stringent exclusion of water and oxygen that the previous method (Me4Sn plus WCl6) required. Low pressures appear to favor polymerization by removing the alkene by-products. The metathesis reaction has been shown to be effective for many unsaturated vegetable oils, although some cases require oil pretreatment with silica gel. This process is effective on a 2–200 g scale. Chromatographic separation and characterization of metathesized soybean oil indicate that the process involves intermolecular and intramolecular carbon-carbon double-bond formation.
TL;DR: With skillful experimentation and careful selection of substrate, alkyne metathesis can result in both ring opening/ring closing and the formation of high molecular weight polymers.
Abstract: Conceptually and mechanistically (!) the metathesis of disubstituted alkynes in the presence of molybdenum or tungsten catalysts (see scheme) is related to alkene metathesis. With skillful experimentation and careful selection of substrate, alkyne metathesis can result in both ring opening/ring closing and the formation of high molecular weight polymers.
TL;DR: A conceptionally new strategy affording these structures is described for the syntheses of (+)-exo-brevicomin and rac-endo- and enantiomerically enriched (+)-endo-Brevicomin, employing desymmetrization of trienes derived from diols with C2 and meso symmetry via ring-closing metathesis.
TL;DR: The allenylidene-ruthenium(II) complex as discussed by the authors was pro-duced in a one-pot reaction from commercially available [RuCl2(p- cymene)]2, catalyses the ring-closing metathesis of N,N-diallyltosylamide at room temperature whereas 2b (X-=BF4-) favored the cyclization of the 1,6-diene 3 into the five-membered heterocycle 5 without loss of atoms.
Abstract: The allenylidene-ruthenium(II) complex [(p-cymene)(PCy3)Cl- RuξCξCξCPh2]+X-, 2a, (X-=CF3SO3-), which is pro-duced in a one-pot reaction from commercially available [RuCl2(p- cymene)]2, catalyses the ring-closing metathesis of N,N-diallyltosylamide at room temperature whereas 2b (X-=BF4-) favours the cyclization of the 1,6-diene 3 into the five-membered heterocycle 5 without loss of atoms. The addition of BF3·OEt2 to 2b restores its selectivity in the RCM reaction. Catalyst 2a also promotes the metathesis of the ene-yne 6 to produce the 3-vinyl-2,5-dihydrofuran 7.
TL;DR: The application of the ring-closing metathesis (RCM) reaction to the construction of a wide variety of nitrogen-containing ring systems is described in this article, where the examples include pyrrolizidine, indolizidine and quinoline derivatives related to azasugars.
TL;DR: In this paper, the preparation of a polymer-supported ruthenium alkylidene metathesis catalyst is described, which is used to initiate a ring-opening metathesizing polymerization of norbornene derivatives onto a polymer support to prepare novel highloading resins for use in combinatorial chemistry.
TL;DR: In this article, a variety of polyethers were synthesized by a tandem approach incorporating ring-closing metathesis (RCM) followed by ring-opening polymerization (ROMP) using RuCl_2(=CHPh)(PCy_3)_2 (1) as an initiator.
Abstract: A variety of polyethers were synthesized by a tandem approach incorporating ring-closing metathesis (RCM) followed by ring-opening metathesis polymerization (ROMP) using RuCl_2(=CHPh)(PCy_3)_2 (1) as an initiator. Unsaturated crown ether monomers, including a 12-crown-4 analogue (3), a benzocrown ether (8), and a benzocrown ether with a pendent phenylalanine methyl ester (9), were synthesized in good yields using a lithium ion as a template and 1 as a catalyst for RCM. Saponification of 9 afforded the benzocrown phenylalanine carboxylic acid monomer 10. The ROMP of 3, 8, and 9 with 1 as an initiator yielded the homopolymers 11, 12e, and 13e, respectively. The relative concentrations of 3 to 1 were varied to produce 11 with a wide range of molecular weights (M_n from 10 900 to 206 300). Hydrogenation of 11 proceeded quantitatively to yield a saturated polyether. Monomers 8 and 9 were copolymerized with 3 to generate polymers 12a−d and 13a−d, respectively. The copolymer composition corresponded to the feed ratio of the monomers. Crown ether 10 was copolymerized with 3 at a low feed ratio to form the corresponding polyether with pendent amino acids.
TL;DR: The construction of polycyclic ethers by sequential ring-closing metathesis and stereoselective hydroboration of enol ethers has been explored in this article.