Oxidative coupling of 5-membered heterocycles catalyzed by a Pd(II)-heteropolyacid system in dimethylformamide

Oxidative coupling of thiophene and 2-methylfuran to the corresponding dihetaryls in DMFA medium occurs in the presence of the homogeneous catalytic system Pd(II)-molybdovanodophosphoric heteropolyacid (HPA). The data obtained show that HPA may act as a reversible oxidant in polar aprotic media.

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, Pd(II)- 2- . , .

     

Oxidative coupling of 5-membered heterocyclic compounds catalyzed by palladium(II)

Coupled heterocycles (bithiophenes, bifurans, furyl thiophenes) have been obtained in high yields via the reaction of thiophene and furan with palladium salts in solution at 50–100°C.

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50–100° (, , ) .

     

Oxidative coupling of furan derivatives to bifurans catalyzed by palladium(II)

Furan and its 2-substituted derivatives (substituents: –CH₃, –CHO, –COOCH₃, –COOC₂H₅, –CH(OOCCH₃)₂) have been shown to react with palladium acetate in solution at 90–130°C giving the corresponding bifuran derivatives in high yields. The following order of activities has been obtained: –H, –CH₃, –CHO>–COOCH₃, –COOC₂H₅, –CH(OOCCH₃)₂>–COOH, which corresponds to the substituent effect in electrophilic substitution in heteroaromatic compounds.

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, 2- (: –CH₃, –CHO, –COOCH₃, –COOC₂H₅, –CH(OOCCH₃)₂) 90–130° . : –H, –CH₃, –CHO>–COOCH₃, –COOC₂H₅, –CH(OOCCH₃)₂>–COOH, .

     

Aqueous Suzuki coupling reaction catalyzed by water-soluble diimine/Pd(II) systems

A series of water-soluble diimine ligands were applied for the Suzuki reaction of arylbromide in different media. Low loading of catalyst (0.01 mol%) were necessary for the coupling reaction to proceed in water or water/ethanol. The catalytic system was found to tolerate a broad range of functional groups.     

Oxidative coupling of alkylbenzenes to diaryls catalyzed by the palladium(II)-heteropolyacid system

Oxidative coupling of alkylbenzenes (benzene, toluene, o-xylene, durene) is shown to proceed in the presence of palladium salts and heteropolyacids under the action of oxygen with a high yield of diaryls. The addition of mercury salts and variation of the solvent affect the reaction rate and isomer composition of the products.

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, (, , -, ) . .

     

Intramolecular arylation of benzimidazoles via Pd(II)/Cu(I) catalyzed cross-dehydrogenative coupling

Electron poor benzimidazole substrates were arylated via an intramolecular cross-dehydrogenative coupling (CDC) reaction. These CDC reactions were catalyzed by a Pd(II)/Cu(I) catalyst system, capable of producing moderate yields on a large library of substrates. The substrate scope consisted of tethered arene-benzimidazoles that upon coupling, produced a fused polycyclic motif.     

Oxidative coupling of NH isoquinolones with olefins catalyzed by Rh(III)

Rh(III)-catalyzed oxidative coupling reactions between isoquinolones with 3-aryl groups and activated olefins have been achieved using anhydrous Cu(OAc)(2) as an oxidant to give tetracyclic products. The nitrogen atom acts as a directing group to facilitate ortho C-H activation. This reaction can be one-pot starting from methyl benzohydroxamates, without the necessity of the isolation of isoquinolone products. A broad scope of substrates has been demonstrated, and both terminal and internal activated olefins can be applied. In the coupling of N-methylmaleimide, a Wacker-like mechanism was proposed, where backside attack of the NH group in isoquinolones is suggested as a key step. Selective C-H activation has also been achieved at the 8-position of 1-naphthol, leading to an olefination product.     

Suzuki coupling catalyzed by a homoleptic Pd(I)-Pd(I) solvento complex

The Pd^I-Pd^I bonded complex [Pd₂(CH₃CN)₆][SbF₆]₂ is catalytically active towards Suzuki cross-coupling reactions of aryl bromides or chlorides with various arylboronic acids under mild conditions giving good to excellent yields. Its performance is enhanced by the introduction of stoichiometric or limited phosphines. The effects of different ligands, metal oxidation states [Pd(II), Pd(I) Pd(0)], bases and solvents have been examined.     

Oxidative homocoupling of arylboronic acids catalyzed by a 4‐aminoantipyrine–Pd(II)complex

A one‐step synthesis of symmetric biaryls is reported under very mild conditions via the homocoupling reaction of substituted arylboronic acids using an air‐ and moisture‐stable 4‐aminoantipyrine–Pd(II) complex as catalyst. The reaction is conducted at a low catalyst loading of 0.1 mol% at room temperature in methanol in the presence of K₂CO₃ as the base and KMnO₄ as the oxidant. The catalytic methodology is shown to be compatible with diverse functional groups and affords the desired biphenyls in good to excellent yields. Copyright © 2015 John Wiley & Sons, Ltd.     

New heteroannulation reactions of N-alkoxybenzamides by Pd(II) catalyzed C-H activation

A new palladium(II) catalyzed methodology for the direct synthesis of alkylidene isoindolinones from N-alkoxybenzamides is presented. Isoindolinone formation proceeds through a highly efficient and E-selective C-H activation/Heck/Aza-Wacker sequence. Substoichiometric amounts of benzoquinone can be employed in a cooperative oxidation system with O(2), leading to facile purification of products. Modification of the reaction conditions provides a general route to substituted phthalimides by carbonylation with CO. Both systems were found to tolerate a wide range of functionality.     

Rapid Suzuki‐Miyaura cross‐coupling reaction catalyzed by zirconium carboxyphosphonate supported mixed valent Pd(0)/Pd(II) catalyst

Mixed valent Pd(0)/Pd(II) nano‐sized aggregates supported onto a chemically robust layered zirconium carboxyphosphonate framework is prepared and its catalytic activity in Suzuki‐Miyaura cross coupling reaction is explored. The exceptionally high catalytic efficacy of the heterogeneous catalyst in Suzuki‐Miyaura cross coupling reaction is signified by remarkably short reaction time 2 minutes and high turnover frequency of 1.3 x 10⁴ hr^?1. The catalyst can be recycled several times without significant loss of catalytic efficacy, while spectroscopic, structural and microscopic investigations suggest the integrity of the catalyst even after fifth catalytic cycle. The unique ability of the zirconium carboxyphosphonate framework to interact strongly with palladium in dual Pd(0)/Pd(II) oxidation states has been attributed to this remarkable augmentation of catalytic efficacy.     

Oxidative phenol coupling catalyzed by polymer-bound copper-imidazole complexes

Polymer-bound imidazole-copper(II) complexes were investigated and applied as catalysts for oxidative coupling (polymerization) of 2,6-dialkylphenols. These polymeric catalysts were also immobilized on silica particles through adsorption, quaternization and grafting. Especially, the grafted catalysts showed interesting catalytic properties, e.g. good specificity for C-O coupling and very good stability during prolonged use in continuous processes. This stability furnished new information about the mechanism of the oxidative coupling polymerization. Finally, this reaction was optimized for the preparation of PPO-type telechelics.     

Kinetics and mechanism of cyclohexene hydrocarbomethoxylation catalyzed by a Pd(II) complex

The kinetics of cyclohexene hydrocarbomethoxylation catalyzed by the Pd(PPh₃)₂Cl₂-PPh₃-p-toluenesulfonic acid (TSA) is reported. The reaction is first-order with respect to cyclohexene and TSA and of order 0.5 with respect to Pd(PPh₃)₂Cl₂. The reaction rate as a function of CO pressure or methanol or PPh₃ concentration passes through an extremum. The chloride anion inhibits the reaction. A mechanism involving cationic hydride complexes as intermediates is suggested. A rate equation is set up by the quasi-steady-state treatment of experimental data.     

Oxidative coupling of porphyrins using copper(II) salts

A method for radical coupling of porphyrins using copper(II) salts as one-electron oxidants was developed. A Zn(II)-porphyrin bearing an aminophenyl group yielded porphyrin oligomers, and two tri-arylporphyrins were oxidized to form doubly and triply linked dimers. Bromination of doubly linked dimers gave macrocycles with twisted skeletons.     

Oxidative decolorization of indigo caramine dye with chloramine-T catalyzed by cobalt(II)

Decolorization of indigo caramine dye by oxidation process using chloramine-T as oxidant and Co(II) as catalyst in acidic buffer media, pH 5.8 has been kinetically studied at 300 K. Decolorization of indigo caramine dye was followed spectrophotometrically. Decolorization and oxidation led to a decrease in Chemical Oxygen Demand of the dye. The Co(II)-catalyzed reaction shows first-order dependence of the rate on chloramine-T and indigo caramine concentrations. It also shows fractional order dependence on [Co(II)] and [H⁺]. Addition of halide ions or reduction product of chloramine-T toluenesulfonamide, and variation of ionic strength and dielectric constant of the medium do not have any significant effect on the reaction rate. Activation parameters are evaluated from the Arrhenius plot, and a mechanism is proposed for the reaction.     

Microwave-assisted aqueous Suzuki coupling reactions catalyzed by ionic palladium(II) complexes

Suzuki coupling is one of the most powerful methods for the synthesis of biaryls. We have prepared and characterized a series of unsymmetrical sulfonated water-soluble Pd(II)-pyridyl imine complexes and investigated them as catalysts for the Suzuki cross-coupling reaction in water under microwave irradiation. The compounds proved to be effective catalysts.     

Carbonylation of styrenes catalyzed by bioxazoline Pd(II) complexes: mechanism of enantioselectivity

Preliminary studies of the elementary steps involved in the reaction of a chiral methyl carbonyl bioxazoline Pd(II) complex with aromatic olefins and CO have allowed development of a new enantioselective catalytic carbonylation process, leading to γ-ketoester derivatives with high yield and good enantiomeric excess. The intermediate palladacycle complexes have been isolated and characterized by NMR spectroscopy and X-ray diffraction. Factors that govern the stereoselectivity of the olefin carbonylation process are discussed.     

Highly efficient Suzuki-Miyaura coupling reactions catalyzed by bis(oxazolinyl)phenyl-Pd(II) complex

Bis(oxazolinyl)phenyl-palladium(II)(Phebox-Pd) complexes were found to be efficient catalysts for Suzuki-Miyaura coupling reactions of aryl boronic acids and their derivatives with aryl halides to give the corresponding biaryl products in high yield along with moderate enantioslectivities in the case of axially chiral induction. The catalytic activity was attained more than 900,000 of TON and 45,000 of TOF. The catalyst can be recovered quantitatively and could be reused for Suzuki-Miyaura reactions.     

Domino allylation and cyclization of ortho-alkynylbenzaldehydes with allyltrimethylsilane catalyzed by Pd(II)-Cu(II) bimetallic systems

The reaction of ortho-alkynylated benzaldehydes 1 with allyltrimethylsilane under the Pd(OAc)₂-CuCl₂ catalyst system gave the isochromene derivatives 2 together with the chlorinated products 3. When the reaction was conducted in the presence of half equiv of H₂O, the formation of 3 was suppressed and 2 was obtained in good to high yields. When the reaction of 1a was carried out with trimethylsilylcyanide instead of allylsilane, the cyano group-substituted isochromene 9 was obtained in 94% yield.