Phosphine-free Conditions Research Articles

Mono- and β,β-Double-Heck Reactions of α,β-Unsaturated Carbonyl Compounds in Aqueous Media

Optimized reaction conditions for the mono- and beta,beta-diarylation of electron-deficient alkenes in aqueous media catalyzed either by a p-hydroxyacetophenone oxime-derived palladacycle or by palladium(II) acetate under phosphine-free conditions and in the presence of (dicyclohexyl)methylamine as base are described. Regioselective monoarylation of unsubstituted and substituted alpha,beta-unsaturated carbonyl compounds takes place with aryl iodides at 120 degrees C in water. Aqueous N,N-dimethylacetamide (DMA), tetra-n-butylammonium bromide (TBAB) as additive, and the palladacycle as catalyst are the most efficient conditions for the coupling with aryl bromides, good stereoselectivities being also obtained in the arylation of crotonates and itaconates, whereas cinnamic derivatives afford lower steroselectivity, with the exception of cinnamic acid and nitrile. beta,beta-Diarylation of unsubstituted alpha,beta-unsaturated carbonyl compounds can be controlled by using higher loading of the palladacycle and can be performed in refluxing water for aryl iodides, whereas DMA must be used for aryl bromides. Microwave irradiation can be used in the monoarylation of tert-butyl acrylate with aryl iodides in water or the coupling between ethyl cinnamate and aryl bromides in aqueous DMA.

Heck‐Type Arylation of 2‐Cycloalken‐1‐ones with Arylpalladium Intermediates Formed by Decarboxylative Palladation and by Aryl Iodide Insertion.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Heck-type arylation of 2-cycloalken-1-ones with arylpalladium intermediates formed by decarboxylative palladation and by aryl iodide insertion.

[reaction: see text] A palladium-catalyzed decarboxylative arylation reaction was shown to produce Heck-type coupling products using a number of different arene carboxylic acid and 2-cycloalken-1-one substrates. The more conventional Heck coupling of an aryl iodide and a 2-cycloalken-1-one reactant was also briefly explored for comparison, where it was found that phosphine-free (Jeffery) conditions afforded the highest yield of product.

Highly Efficient, Recyclable Pd(II) Catalysts with Bisimidazole Ligands for the Heck Reaction in Ionic Liquids.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Highly efficient, recyclable Pd(II) catalysts with bisimidazole ligands for the Heck reaction in ionic liquids.

[reaction: see text] New Pd(II) complexes with bisimidazole ligands were prepared and proved to be effective catalysts for the Heck reaction under phosphine-free conditions using ionic liquids as solvents. This system could be recycled five times without any loss of catalytic activity.

Highly Active Pd(II) Catalysts with trans‐Bidentate Pyridine Ligands for the Heck Reaction.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Highly active Pd(II) catalysts with trans-bidentate pyridine ligands for the Heck reaction.

[reaction: see text] The air-, water-, and heat-stable palladium(II) complexes 2a and 2b are prepared by the reaction of palladium(II) salts with the new trans-bidentate nitrogen ligands, 1,2-bis(2-pyridylethynyl)benzenes. The structure of complex 2a has been confirmed by X-ray structure analysis. The complexes efficiently catalyze the Heck olefination of aryl iodides and provide a good yield under phosphine-free conditions. The reaction is very sensitive to the nature of the chelating ligand.

Heck arylations of N-acyl-3-pyrroline and N-acyl-1,2,5,6-tetrahydropyridine with aryldiazonium salts. Short syntheses of aryl γ- and δ-lactams, baclofen, homobaclofen and analogues

Heck arylation of N-acyl-3-pyrrolines and an N-acyl-tetrahydropyridine with aryldiazonium tetrafluoroborates under phosphine-free conditions proceeded smoothly to give α-hydroxycarbamates (hemiaminals) or α-alkoxycarbamates which were oxidized to the desired γ- and δ-lactams. Acidic hydrolysis of the γ-lactams produced a series of arylated GABA derivatives, including baclofen, a useful therapeutic drug, in only three steps with an overall yield of 63–76%. Starting from N-acyl-tetrahydropyridine, aryl-δ-lactams and higher homologues of baclofen can be obtained.

Heck Reactions Catalyzed by PAMAM-Dendrimer Encapsulated Pd(0) Nanoparticles

The behavior of PAMAM-dendrimer encapsulated palladium nanoparticles as catalysts for the Heck reaction has been examined, and it has been demonstrated that this simple system is a very efficient catalyst giving good yields under phosphine-free conditions and with 200−400 times less Pd than usual.