Showing papers on "Heck reaction published in 1999"
TL;DR: In the last three years, there have been tremendous developments in palladium catalytic systems for Heck type reactions as mentioned in this paper, and one of the successful approaches towards activation of less reactive substrates like aryl chlorides involves the use of palladacycles 1, 2 and 3 as catalyst precursors.
516 citations
TL;DR: In this article, it is established that new reactive anionic palladium(0) complexes species are formed in which palladium is ligated by either chloride ions or acetate ions.
425 citations
TL;DR: In this paper, aryl halides or benzoic anhydride with alkenes can be performed with excellent yields in room-temperature ionic liquids, which provide a medium that dissolves the palladium catalyst and allows the product and byproducts to be easily separated.
408 citations
TL;DR: In this article, the 1,3,4,5-tetramethylimidazol-2-ylidene ligand (tmiy) has been synthesized and the X-ray crystal structures of complexes 8 and 10 reveal square-planar coordination with the carbene ligands inclined at significant angles to the coordi...
376 citations
TL;DR: A pincer-type SCS ligand containing Pd(II) is a simple, robust catalyst for Heck chemistry using a variety of alkene acceptors and aryl iodides as discussed by the authors.
Abstract: A new pincer-type SCS ligand containing Pd(II) is a simple, robust catalyst for Heck chemistry using a variety of alkene acceptors and aryl iodides. It is less active with aryl bromides. While certain palladium(II) species insert slowly into the aryl C−H bond of an unsubstituted version of this ligand, the introduction of activating groups into the 5 position of the aromatic ring readily allows quantitative metal insertion. These ligands were synthesized and attached to soluble polymers by simple modification of inexpensive starting materials. For example, both 5-oxy and 5-amido SCS ligands were successfully appended to 5000 Mn poly(ethylene glycol) via ether or amide linkages, respectively. Both the 5-oxo and 5-amido complexes are active as Heck catalysts in DMF solution in air. The PEG-bound 5-amido-SCS−Pd complex was recycled via solvent precipitation three times with no observed catalyst deactivation. While the 5-amido-SCS−Pd complexes are very robust, their 5-oxo counterparts decompose slowly under c...
259 citations
TL;DR: Comparisons with results from serial GC analysis showed that the fluorescence-based assay accurately selected the most active ligands for the Heck coupling of aryl bromides and chlorides.
Abstract: A new fluorescence-based assay for high-throughput screening of reactions that couple two organic molecules is described. The assay involves reaction of one substrate containing a tethered fluorophore with a second molecule that is attached to a solid support. A successful coupling process is signaled by fluorescence of the solid support, which can be isolated by either simple centrifugation or filtration. To evaluate this assay in the context of a catalytic process under intense current study, we searched for improved, readily available phosphines for Heck chemistry. An acrylate containing a tethered coumarin was reacted with an aryl halide supported on a cross-linked polystyrene resin. Comparison of the results from our fluorescence-based assay with results from serial GC analysis showed that the fluorescence-based assay accurately selected the most active ligands for the Heck coupling of aryl bromides and chlorides. Two ligands chosen by the assay, tri(tert-butyl)phosphine and di(tert-butylphosphino)fe...
259 citations
TL;DR: A series of homopolymer-stabilized Pd colloids with varying metal particle size was used to study the Heck coupling reaction between aryl halides and olefins.
Abstract: A series of well-defined homopolymer-stabilized Pd colloids with varying metal particle size was used to study the Heck coupling reaction between aryl halides and olefins. Correlation of initial reaction rates and particle sizes determined by transmission electron microscopy demonstrates that the Heck reaction is a sensitive probe of metal surface structure. The presence of the colloid-stabilizing homopolymer affords a much more stable catalyst than that obtained using the colloid−precursor metal complexes alone. Extremely high total turnover numbers (TON, moles of substrate/moles of Pd; TON = 100 000) and turnover frequencies (TOF = TON/h; TOF > 80 000) are easily attainable with poly(vinylpyrrolidone)-stabilized colloidal palladium in the coupling of p-bromobenzaldehyde with butyl acrylate.
255 citations
TL;DR: In this paper, the use of nonaqueous ionic liquids (NAILs) as an alternative to traditional molecular solvents for the Heck reaction has been shown to result in easy product separation, possible catalyst recycling and further increases in catalyst productivity.
200 citations
TL;DR: The cyclopalladated, phosphine-free imine complexes 1 and 3 are exceptional catalysts for Heck arylation, leading to more than a million turnovers in some cases as discussed by the authors.
158 citations
TL;DR: In this paper, a new catalyst system consisting of dicyclohexylamine or methyl(dicycloehexyl)amine and a phase-transfer catalyst was proposed for trisubstituted olefins.
Abstract: Trisubstituted olefins are easily accessible under mild reaction conditions using a new catalyst system consisting of dicyclohexylamine or methyl(dicyclohexyl)amine and a phase-transfer catalyst (see equation). The choice of the base was found to be crucial for the stereoselectivity and the rate of Heck type arylation reactions.
146 citations
TL;DR: The Heck reaction has been applied to a number of new concepts starting from simple, oligohalogenated alkenes and arenes, and the synthesis of a variety of highly functionalized carbon skeletons has been established.
TL;DR: The first enantioselective total synthesis of scopadulcic acid was described in this article, where the key step is a cascade intramolecular Heck reaction of a methylenecycloheptene iodide.
Abstract: The first enantioselective total synthesis of scopadulcic acid A is described. The key step is a cascade intramolecular Heck reaction of a methylenecycloheptene iodide, which generates the B, C, and D rings of the scopadulan ring system in 90% yield as a single stereoisomer. A distinctive feature of these syntheses is the use of stereoselective enolization to dictate which enantiomer of the natural product is produced.
TL;DR: In this paper, the Heck reaction of aryl bromides with styrene was investigated and it was shown that the electronic properties of the arybromide have a dominating effect on the reaction yield.
Abstract: Palladium modified zeolites exhibit a high activity towards the Heck reaction of aryl bromides with styrene for small Pd concentrations (=0.2 mol%). The catalysts can be easily separated from the reaction mixture and reused without loss in activity. Leaching of active Pd species was observed in dependence on the zeolite structure. The electronic nature of the aryl bromide has a dominating effect on the reaction yield and the results observed are consistent with an oxidative addition of the aryl bromide to a Pd(0) centre via a S N Ar route.
TL;DR: Complex 1b shows an unprecedented high activity in the Heck reaction as mentioned in this paper, and it is shown that in this system not the oxidative addition but the alkene coordination/migratory insertion is the rate determining step.
Abstract: Complex 1b shows an unprecedented high activity in the Heck reaction. Kinetic studies show that in this system not the oxidative addition but the alkene coordination/migratory insertion is the rate determining step.
TL;DR: The Heck reaction is a powerful method for the synthesis of both tertiary and quaternary chiral carbon centres, with enantiomeric excesses (ees) often around 80% and in some cases much higher as discussed by the authors.
TL;DR: A comparison of liquid- and solid-phase reactions reveals a surprising superiority of theSolid-phase reaction in selectively forming C-C bonds.
Abstract: Up to nine C-C bonds are formed selectively from up to seven components starting from an alkene, a haloarene, and a dienophile [Eq. (1)]. A comparison of liquid- and solid-phase reactions reveals a surprising superiority of the solid-phase reaction.
TL;DR: Heavy metals can be avoided with a new radical equivalent of the Heck reaction for aliphatic derivatives in which iodide and dithiocarbonate substituents are replaced by substituted vinyl groups.
Abstract: Heavy metals can be avoided with a new radical equivalent of the Heck reaction for aliphatic derivatives in which iodide and dithiocarbonate substituents are replaced by substituted vinyl groups [Eq. (1)]. The reaction enables the introduction of vinyl fragments into a variety of functionalized substrates.
TL;DR: Fifteen steps suffice for an enantioselective total synthesis of (-)-strychnine from 1,3-cyclohexanedione, including the easy generation of the enantiopure intermediate 2, the closure of the piperidine ring by a reductive Heck reaction, and the elaboration of the indoline nucleus in an advanced synthetic stage.
Abstract: Fifteen steps suffice for an enantioselective total synthesis of (-)-strychnine (1) from 1,3-cyclohexanedione. The key steps are the easy generation of the enantiopure intermediate 2, the closure of the piperidine ring by a reductive Heck reaction, and the elaboration of the indoline nucleus in an advanced synthetic stage. TBDMS=tert-butyldimethylsilyl.
TL;DR: In this paper, MAS-NMR was used to characterize the Heck reaction of aryl bromides with olefins for small palladium concentrations (0.1 mol%).
TL;DR: A modified clay material, prepared by intercalating palladium chloride and tetraphenylphosphonium bromide into montmorillonite K10 clay, catalyzes the Heck reaction and affords trans -stilbenes in high yields as mentioned in this paper.
TL;DR: A complex molecular reorganization, a sequential anionic aza-Cope rearrangement and Mannich cyclization, and an unprecedented intramolecular Heck reaction of the tetrasubstituted double bond of a vinylogous carbamate are key steps in a new total synthesis of (+/-)-gelsemine.
Abstract: Acomplexmolecularreorganization (1→2), a sequential anionic aza-Cope rearrangement and Mannich cyclization, and an unprecedented intramolecular Heck reaction of the tetrasubstituted double bond of a vinylogous carbamate are key steps in a new total synthesis of (±)-gelsemine (3). MOM=methoxymethyl, DBU=1,8-diazabicyclo[5.4.0]undec-7-ene.
TL;DR: Efficient Heck reactions under aerobic conditions were carried out using Pd-catalyst in the presence of CaCO 3, under these conditions a neat Heck Reaction using arenediazonium salts bearing functional groups including nitro functionalities can generally take place in good yields up to 95% as mentioned in this paper.
TL;DR: In this article, the regeneration of PhPdOAc species from Ph 2 SbCl, HPdOCl, and oxygen is proposed as a key step in the catalytic cycle where oxygen-containing radical species might be present as intermediates.
TL;DR: Analogs of the cytokinins trans-zeatin and benzylaminopurine have been prepared by Heck coupling on 6-vinylpurines or Sonogashira coupling on six-halopurines as key-steps, and their cytokinin activity has been evaluated based on their ability to stimulate increased growth in radish cotyledons.
TL;DR: In this paper, the authors used homogeneous Pd(OAc)2 catalyst in octane, toluene, N-methylpyrrolidone, acetonitrile, ethanol and N,N′-dimethylacetamide solvents with various triphenylphosphine (PPh3) concentrations.
Abstract: The vinylation of methyl acrylate and iodobenzene was studied using the homogeneous Pd(OAc)2 catalyst in octane, toluene, N-methylpyrrolidone, acetonitrile, ethanol and N,N′-dimethylacetamide solvents with various triphenylphosphine (PPh3) concentrations In polar solvents the rate of reaction is very high as compared with nonpolar solvents In polar solvents the rate of reaction shows significant drop with increase in PPh3 concentration whereas in nonpolar solvents it passes through a maximum at a PPh3/Pd ratio of 2 There is no effect of different bases such as Et3N and KOAc on the dependence of the rate of reaction on the PPh3/Pd ratio These results are explained based on Heck reaction mechanism previously proposed
TL;DR: In this article, it was shown that the Pd-catalyzed enantioselective Heck reaction of p-XC6H4OTf, X = OMe, H, CO2Me, with dihydrofuran gives higher enanti-lectivities when the chelating diphosphine MeO−Biphep, 1a, is replaced with its disubstituted analogue 3,5-di-tert-butyl MeO+Biphesp, 2b, 1b.
TL;DR: In this article, the Heck reaction was performed in perfluorinated solvents, using perfluorsocarbon-soluble triarylphosphines as ligands.
TL;DR: The optically active clavicipitic acid (4), an ergot alkaloid, was synthesized by a three-step sequence from 4-bromoindole as discussed by the authors.
TL;DR: In this paper, a Heck vinylation reaction using Pd (OAc) 2 / TPPTS catalyst system in supercritical carbon dioxide was studied using co-solvents such as water and ethylene glycol significantly enhances the rate of reaction without leaching of Pd into the product phase.
TL;DR: A novel route to fused indoles via two consecutive palladium catalyzed reactions, an intramolecular Heck reaction followed by a reductive N-heteroannulation, has been developed as discussed by the authors.