Showing papers on "Heck reaction published in 1998"
TL;DR: A variety of methylpalladium carbene complexes of the type [Pd(Me)(carbene)(chelate)] have been synthesized and fully characterised as mentioned in this paper, where carbene=1,3-di-methylimidazol-2-ylidene (DMiy), chelate=acetylacetonate (acac) 1, trifluoroacetylACetonate(tfac) 2, hexafluoro-acetylacetyl-acetonates (hfac) 3, carbene = 1,3
208 citations
TL;DR: A simple solution to the age-old problem of the Heck reaction of cheap but unreactive chloro- and bromoarenes has been found in the catalyst [Pd(CH3 CN)2 Cl2 ]⋅6 Ph4 PCl in the presence of N,N-dimethylglycine as additive.
Abstract: We sought a peptidic self-replicatingsystem that would be sensitive to environmental conditionsand reproduce only under extreme conditions. We nowdescribe a peptide that reproduces autocatalytically in anenvironmentally dependent manner.The peptide K1K2 (Figure 1) was designed based on thesequence of the KK peptide of Zhou et al.
190 citations
DSM1
TL;DR: A new variant of the Heck reaction in which no halogen salts are formed can be achieved by the use of aromatic carboxylic anhydrides 1 as arylating agents for arylated olefins in good yields.
Abstract: Environmentally benign and economical production of arylated olefins can be achieved by a new variant of the Heck reaction in which no halogen salts are formed. The trick is the use of aromatic carboxylic anhydrides 1 as arylating agents. With halide-activated palladium chloride as catalyst, which requires no phosphane ligands, the olefins 2 can be prepared according to Equation (a) in good yields.
150 citations
TL;DR: The Heck reaction has been computationally studied for a carbene-stabilized palladium catalyst employing a density functional method with a gradient-corrected exchange-correlation functional as mentioned in this paper.
142 citations
TL;DR: Palladium salts such as Pd(OAc) 2 or PdCl 2 (PhCN) 2 in the presence of N,N -dimethyl glycine (DMG) constitute the simplest and one of the most reactive and selective catalyst systems for the Heck reaction of aryl bromides with olefins known to date.
131 citations
TL;DR: In this article, the Suzuki cross-coupling reaction of a boronic acid and a bromoaromatic compound requires palladium catalysis, and almost identical yields were obtained in the usual conditions, with 30 mequiv.
126 citations
TL;DR: In this article, a mechanism based on a PdII-PdIV cycle was proposed for separating the product from the catalyst, which involves treatment with cyanide ion. But this method was not suitable for the case of pure tri(1-naphthyl)phosphine.
122 citations
TL;DR: An orthopalladated complex of commercially available tris(2,4-di- tert -butylphenyl)phosphite proves to be an extremely active catalyst in the Heck arylation of alkenes, with turnover numbers of up to 5,750,000 (mol product) as mentioned in this paper.
108 citations
TL;DR: In this paper, the Heck-type reaction with the mixture of Pd(OAc) 2 and n-Bu 4 NBr as a catalytic system was applied to different derivatives and proved to be compatible with sensitive functional groups.
98 citations
TL;DR: An efficient catalytic approach to steroids by a double Heck reaction of the vinyl bromides and the CD-building block is presented in this paper, where the new estrogen analogues 1a and 1b are formed via 23a...
Abstract: An novel efficient catalytic approach to steroids by a double Heck reaction of the vinyl bromides 2 and the CD-building block 3 is presented. The new estrogen analogues 1a and 1b are formed via 23a...
96 citations
TL;DR: In this article, X-Ray diffraction and transmission electron microscopy (TEM) with selected area electron diffraction (SAED) techniques were carried out to ascertain the nature, size and morphology of the Pd clusters.
Abstract: Nanoscale particles of palladium metallic clusters have been prepared at room temperature by sonochemical reduction of a 1:2 molar mixture of palladium acetate, Pd(O2CCH3)2 , and myristyltrimethylammonium bromide, CH3(CH2)12N(CH3)3Br (NR4X), in tetrahydrofuran (THF) or methanol. Apart from its stabilizing effect, NR4X acts as a reducing agent, probably due to the decomposition that occurs at the liquid-phase region immediately surrounding the collapsing cavity, and provides reducing radicals. Addition of 0.2 m ethanol–methanol in the THF process enhances the sonochemical reduction of PdII because of its highly volatile nature producing various reducing radicals inside the collapsing bubble. Analyses by UV–VIS spectroscopy indicated the initial formation of a PdII–NR4X complex, which, in turn, reduced to Pd0 . Elemental analysis of the resulting solid (sonication residue) shows that the THF process yields NR4X stabilized-palladium clusters, whereas the methanol process shows the formation of pure Pd agglomerates. X-Ray diffraction (XRD) and transmission electron microscopy (TEM) with selected area electron diffraction (SAED) techniques were carried out to ascertain the nature, size and morphology of the Pd clusters. TEM of NR4X stabilized-Pd shows the presence of spherical particles of 10–20 nm in size. Selected area electron diffraction (SAED), along with TEM, reveals that the pure Pd consists of dense agglomerates, whereas NR4X stabilized-Pd exists as thin crystallites. These Pd nanoclusters are catalytically active towards carbon–carbon coupling, or Heck reaction, in the absence of phosphine ligands, to a moderate extent of 30% conversion. Hydrogenation of cyclohexene to cyclohexane has also been studied using sonochemically generated Pd materials. The catalytic ability of these Pd materials was compared with the commercial Pd on carbon material.
TL;DR: The triazene linker is distinguished by its accessibility, thermal robustness, and capability to undergo regeneration.
Abstract: Triazenes as "traceless" linkers for solid-phase synthesis have been utilized for the attachment of arenes to a solid support and yield the corresponding products after various organometallic reactions (Heck reaction and asymmetric dihydroxylation, see the reaction scheme) and cycloadditions (Diels-Alder reaction). The triazene linker is distinguished by its accessibility, thermal robustness, and capability to undergo regeneration.
TL;DR: In this article, the role of base in Heck reactions of 1,1-disubstituted olefins was investigated and the results showed that the nature of the base dramatically influences the product distribution.
Abstract: The coupling reaction of 1,1-disubstituted olefins (α-methylstyrene, n-butyl methacrylate) with various aryl bromides (Heck reaction) has been studied as a new concept to synthesize trisubstituted olefins. Surprisingly, the nature of the base dramatically influences the product distribution. Thus, a systematic investigation on the role of base in Heck reactions of 1,1-disubstituted olefins was performed. Less coordinating bases like NaOAc, NaOBz or Na2CO3 yield a statistical distribution of regioisomers with the terminal olefin 10 as the major product. However, by using amines like Bu3N or diisopropylethylamine (DIPEA) as base internal olefins can be synthesized with high selectivities. With phosphapalladacycle 3 as catalyst precursor, we were able to obtain catalyst turnover numbers up to 1000, while Pd(OAc)2/2PPh3 was one order of magnitude less active. Analysis of the reaction profile by kinetic investigations led to the postulation of a reduction and subsequent oxidative addition of the catalyst precursor 3 to form 12 as catalytically active intermediate.
TL;DR: The sequential or cascade combination of olefin metathesis with intramolecular Heck reactions provides access to fused-, bridged-and spiro-cyclic ring systems in good yield as discussed by the authors.
TL;DR: Palladium (II) chloride complexes of (diisopropylphosphino)ferrocenes act as efficient catalyst precursors for the Heck reaction as discussed by the authors.
TL;DR: Chiral 2-diphenylarsino-2-diaphylphosphino-1,1-binaphthyl (BINAPAs) was synthesized and found to be an effective ligand in an aryl triflate-using asymmetric Heck reaction.
TL;DR: In this article, the Heck reaction was used to obtain the 5- or 6-ring-annelated cis-5,6-disubstituted cyclohexadienes.
TL;DR: Theoretical studies of the Heck reaction between ethene and a methyl electrophile at [Pd(H2ACH2AH2)(CH3)(H2CCH2)]+ (A = P, N) reveal intermediates with an agostic H which is the one preferentially transferred to base as discussed by the authors.
TL;DR: In this paper, an enantioselective total synthesis of (+)-xestoquinone has been achieved using a cascade-type asymmetric Heck reaction in up to 63% ee and 39% chemical yield (66% conversion yield).
TL;DR: The Heck reaction has been extended to the synthesis of bridged rings, spirocycles, and tetrasubstituted carbon centre as discussed by the authors, and the ongoing high level of activity has been further fostered by the advent of a range of additives which variously enhance the rate of Heck reactions, control the rkgioselectivity of the P-hydride elimination step, and suppress double bond isomerisation in the product.
Abstract: Pd(0) catalysts facilitate the assembly of complex heterocycles and carbocycles containing 3 - 7 membered rings from a range of simple building blocks (allenes, carbon monoxide, alkenes, organometallic complexes of B, Zn, Sn etc.). These cascade processes display remarkable chemo-, regio- and stereo-selectivity and considerably extend the scope and utility of our previously developed cyclisation-anion capture cascades. The success of these processes is critically dependant on the relative rates of a range of potentially competing processes and the various substrates can be regarded as queuing for access to the catalytic metal centre. Certain compounds are identified as relay switches because they extend the relay phase of the cyclisation-anion capture cascade whilst allowing the Pd catalysed cascades to switch between inter- and intra-molecular processes. Palladium salts and complexes are exceptionally versatile catalysts for the construction of carbon-carbon and carbon-heteroatom bonds.' Much recent attention has focused on the Heck reaction2 (Scheme 1) due to developments which have considerably enhanced the scope of this palladium-catalysed vinylation of aryl, heteroaryl, vinyl and benzyl halides. Thus the Heck reaction has been extended to the synthesis of bridged rings, spirocycles, and tetrasubstituted carbon centre^.^-^ These latter developments and the ongoing high level of activity have been further fostered by the advent of a range of additives which variously enhance the rate of Heck reactions, control the rkgioselectivity of the P-hydride elimination step, and suppress double bond isomerisation in the product. Thus addition of tetraalkylammonium salts often allow Heck reactions to be carried out at, or near, room temperature in good yield,6 whilst addition of Ag(1) salts' or Tl(I)* salts can control the direction of P-hydride elimination, suppress double bond isomerisation and influence the reaction rate. Tl(1) additives have also proved useful in natural product synthesis.' However, the Heck reaction fails to take advantage of the inherent ability of palladium (0) catalysts to process a wide range of chemically distinctive substrates and suffers from the drawback that, as usually practised, only one C-C bond is made.
TL;DR: The Diels-Alder adduct between cyclopentadiene and the iminium salt of formaldehyde was coupled as its boc-derivative with two aryl iodides as mentioned in this paper.
TL;DR: Synthesis of a complex steroid having cis A B and C D ring fusions and hydroxyl functionality at C-5, C-14 and C-19 is described in this paper.
TL;DR: In this article, a protocol for the efficient direct cross coupling of esters of propiolic acid and of aryl iodides with a Pd(PPh3)2Cl2/copper(I) iodide catalyst system in the presence of K2CO3 has been developed.
TL;DR: In this paper, the stannanes obtained could be used as starting materials for the preparation of various 3,5-di-substituted pyridazines as shown for 3-phenyl-5-tributylstannyl-pyridazine 9b.
TL;DR: In this paper, a facile new synthesis of symmetrical trans-stilbenes, in particular of trans-4,4′-diiodostilbene, by (double) Heck reaction of arenediazonium salts with vinyltriethoxysilane is described.
Abstract: With anilines as the starting materials, a facile new synthesis of symmetrical trans-stilbenes, in particular of trans-4,4′-diiodostilbene, by (double) Heck reaction of arenediazonium salts with vinyltriethoxysilane is described.
TL;DR: In this article, various reaction conditions and catalysts including cyclometallated Pd II -complexes and palladium on activated carbon have been tested for Pd-catalyzed reactions that are assumed to proceed via Pd IV -intermediates or via ligand exchange reactions between Pd I -intermediateates.
TL;DR: The Heck reaction of allyl alcohol with triflates gave 2-allyloxy-3-oxoindole derivatives rather than the 3-substituted indole products as a result of a nucleophilic attack on an acyliminium intermediate.
TL;DR: Intermolecular Heck reaction of a wide variety of aryl/heteroaryl iodides with alkylallenes furnishes 1,3-dienes which undergo in situ Diels-Alder cycloaddition to N-methylmaleimide as discussed by the authors.