Palladium‐catalysed Suzuki reaction of aryl chlorides in aqueous media using 1,3‐dialkylimidazolidin‐2‐ylidene ligands

A highly effective, easy to handle and environmentally benign process for palladium‐mediated Suzuki cross‐coupling is developed. The in situ prepared three‐component system Pd(OAc)₂–1,3‐bis(alkyl)imidazolinium chlorides (2a–f) and Cs₂CO₃ catalyses quantitatively the Suzuki cross‐coupling of deactivated aryl chlorides. Copyright © 2005 John Wiley & Sons, Ltd.     

The Suzuki reaction in aqueous media promoted by P, N ligands

The synthesis and structure of palladium complexes of trisubstituted PTA derivatives, PTA(R3), are described. Water-soluble phosphine ligands 1,3,5-triaza-7-phosphaadmantane (PTA), tris(aminomethyl)phosphine trihydrobromide, tri(aminomethyl) phosphine, 3,7-dimethyl-1,5,7-triaza-3-phosphabicyclo[3,3,1]nonane (RO-PTA), 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (DAPTA), lithium 1,3,5-triaza-7-phosphaadamantane-6-carboxylate (PTA-CO?Li), 2,4,6-triphenyl-1,3,5-triaza-7-phosphatricyclo [3.3.1.1]decane, and 2,4,6-triphenyl-1,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane were used as ligands for palladium catalyzed Suzuki reactions in aqueous media. RO-PTA in combination with palladium acetate or palladium chloride was the most active catalyst for Suzuki cross coupling of aryl bromides and phenylboronic acid at 80 °C in 1:1 water:acetonitrile. The activity of Pd(II) complexes of RO-PTA is comparable to PPh?(m-C?H?SO?Na) (TPPMS) and P(m-C?H?SO?Na)? (TPPTS) and less active than tri(4,6-dimethyl-3-sulfonatophenyl)phosphine trisodium salt (TXPTS). Activated, deactivated, and sterically hindered aryl bromides were examined, with yields ranging from 50% to 90% in 6 h with 5% palladium precatalyst loading. X-ray crystal structures of (RO-PTA)PdCl?, (PTA(R3))?PdCl? (R = Ph, p-tert-butylC?H?), and PTA(R3) (R = p-tert-butylC?H?) are reported.     

Catalytic activity of 1‐methylimidazole‐based phosphine ligands in the palladium‐catalyzed Suzuki coupling reaction

The catalytic activities of three N‐methylimidazole‐based phosphine ligands in the Suzuki coupling reaction were tested using PdCl₂ as the catalyst. The results showed all three phosphine ligands exhibited excellent activity towards the Suzuki reaction, and the catalytic activity decreased with increasing number of imidazole groups. Copyright © 2014 John Wiley & Sons, Ltd.     

Oxygen-promoted PdCl2-catalyzed ligand-free Suzuki reaction in aqueous media

A simple and efficient protocol has been developed for the PdCl(2)-catalyzed ligand-free and aerobic Suzuki reaction of aryl bromides or nitrogen-based heteroaryl bromides with arylboronic acids in good to excellent yields in aqueous ethanol. A systematic investigation on the effect of different atmospheres on the reactivity of the palladium-catalyzed Suzuki reaction has been carried out, the results show that an aerobic atmosphere demonstrates a positive effect on the reactivity of the Suzuki reaction in an aqueous media and a negative effect in a pure organic solvent, which exhibits that the water plays a crucial role for the function of the atmosphere on the palladium-catalyzed ligand-free Suzuki reaction.     

The kinetics and mechanism of polymer-based NHC-Pd-pyridine catalyzed heterogeneous Suzuki reaction in aqueous media

One of the most important challenges of the Suzuki reaction is a green synthesis of reaction products. In terms of economy and ecology, the Suzuki reaction details must be characterized for the industrial-scale Suzuki reaction processes. In this paper, for the first time, a kinetic and mechanistic study on the Suzuki reaction catalyzed with hydrogel-supported PEPPSI (pyridine-enhanced precatalyst preparation stabilization (and) initiation) type NHC-Pd-pyridine composite has been investigated. To determine the rate-limiting step, the effects of reactants and experimental conditions on the heterogeneous Suzuki reaction have been experimentally defined. The experimental results demonstrated that it is possible to reach 100% yield under the optimum reaction conditions, which were found as 75 × 10⁻³ mol/L of phenylboronic acid (FBA), 50 × 10⁻³ mol/L of bromoacetophenone (Brac), 125 × 10⁻³ mol/L of K₂CO₃, 1 g/L of catalyst, 80°C of reaction temperature, 400 rpm of mixing rate, and 3 h of reaction time. The transmetalation step in the cycle was defined as the rate-limiting step. On the basis of kinetic results, a mathematical reaction rate expression was presented assuming the steady-state approach to steps of the catalytic cycle. The activation energy (E_a) of the reaction was estimated to be 34.88 kJ/mol.     

Suzuki reaction of aryl chlorides using saturated N‐heterocarbene ligands

From readily available starting materials, six 1,3‐dialkyl‐imidazolinium bromides ( 2a–f ) have been prepared and characterized by conventional spectroscopic methods and elemental analyses. The incorporation of saturated N‐heterocyclic carbenes into palladium precatalysts gives high catalyst activity in the Suzuki coupling of deactivated aryl chloride substrates in aqueous media. The complexes were generated in the presence of Pd(OAc)₂ by in situ deprotonation of 2a–f . © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:557–561, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20140     

Palladium‐catalyzed regioselective C2‐arylation of 5‐aminoindole

Pd(II)‐catalyzed C‐H arylations of 5‐aminoindole using iodobenzenes as aryl source was studied. Despite pivalamide directing group at 5‐position of the indole, the direct C2‐arylation of the indole observed in high yields and with high regioselectivity.     

Palladium‐catalyzed dehalogenation of 5‐halopyrazoles

A new and efficient method for the dehalogenation of 5‐halopyrazoles was developed by using the catalytic amount of palladium (II) chloride and triphenylphosphine as a ligand at reflux under constant flow of hydrogen gas. The reaction gave the corresponding pyrazole products in good to excellent yields (≥83%). J. Heterocyclic Chem., (2012).     

1‐(α‐Aminobenzyl)‐2‐naphthol as phosphine‐free ligand for Pd‐catalyzed Suzuki and one‐pot Wittig‐Suzuki reaction

Air stable and easily accessible, 1‐(α‐aminobenzyl)‐2‐naphthols are used as efficient phosphine‐free ligands in palladium‐catalyzed Suzuki reaction for a variety of substrates under conventional heating as well as ultrasonic conditions. Multi‐brominated aromatic substrates were successfully converted to corresponding arylated moieties with good conversion and selectivity. A novel one‐pot two‐step cascade reaction strategy involving Wittig and Suzuki reactions is developed for efficient synthesis of 4‐styryl biphenyls (C₆‐C₂‐C₆‐C₆ unit). Copyright © 2012 John Wiley & Sons, Ltd.     

One‐pot synthesis of 2‐acylimino‐3‐aryl‐1,3‐thiazoline derivatives in aqueous media

The one‐pot two‐step synthesis for acyliminothiazolines by treatment of N,N'‐substituted thioureas with α‐bromocarbonyl compounds under aqueous media was described. Compared to classical reaction in organic solvents, this method consistently has the advantages of short reaction time and being environmentally friendly.     

Thermoregulated ligand–palladium‐catalyzed Suzuki reaction in water

An efficient and recyclable protocol for the Suzuki reaction in water has been developed based on the cloud point of thermoregulated ligand Ph₂P(CH₂CH₂O)_nCH₃ (n = 22). This method allows the preparation of a variety of biaryls in high yields and the catalytic system can be recycled four times with high efficiency. Copyright © 2010 John Wiley & Sons, Ltd.     

Palladium‐catalyzed Heck coupling of 2‐vinylpyridine with aryl chlorides

An efficient PdCl₂(PCy₃)₂‐catalyzed cross‐coupling reaction of 2‐vinylpyridine with aryl chlorides to afford trans ‐2‐styrylpyridines with a variety of functional groups on the benzene ring is described. Copyright © 2008 John Wiley & Sons, Ltd.     

Phenylimidorhenium(V) Complexes with 1,3‐Diethyl‐4,5‐dimethylimidazole‐2‐ ylidene Ligands

The phenylimidorhenium(V) complexes [Re(NPh)X₃(PPh₃)₂] (X = Cl, Br) react with the N‐heterocyclic carbene (NHC) 1,3‐diethyl‐4,5‐dimethylimidazole‐2‐ylidene (L^Et) under formation of the stable rhenium(V) complex cations [Re(NPh)X(L^Et)₄]²⁺ (X = Cl, Br), which can be isolated as their chloride or [PF₆]^? salts. The compounds are remarkably stable against air, moisture and ligand exchange. The hydroxo species [Re(NPh)(OH)(L^Et)₄]²⁺ is formed when moist solvents are used during the synthesis. The rhenium atoms in all three complexes are coordinated in a distorted octahedral fashion with the four NHC ligands in equatorial planes of the molecules. The Re–C(carbene) bond lengths between 2.171(8) and 2.221(3) Å indicate mainly σ‐bonding between the NHC ligand and the electron deficient d² metal atoms. Attempts to prepare analogous phenylimido complexes from [Re(NPh)Cl₃(PPh₃)₂] and 1,3‐diisopropyl‐4,5‐dimethylimidazole‐2‐ylidene (L^i?Pr) led to a cleavage of the rhenium‐nitrogen multiple bond and the formation of the dioxo complex [ReO₂(L^i?Pr)₄]⁺.     

无气味、实用的缩硫醛/酮化反应试剂：2-（1，3-二噻-2-亚基）-3-羰基丁酸甲酯

a-Oxo ketene dithioacetals, methyl 2-（1,3-dithian/dithiolan-2-ylidene）-3-oxobutanoate （2a/2b） prepared in nearly quantitative yields simply from methyl acetylacetate, carbon disulfide and 1,3-dibromopropane/1,2-dibromoethane in the presence of potassium carbonate, were investigated in the thioacetalization with various carbonyl compounds 3. It has been demonstrated that methyl 2-（1,3-dithian-2-ylidene）-3-oxobutanoate （2a） could act as a nonthiolic, odorless and practical thioacetalization reagent. A range of aldehydes and ketones 3 were converted into the corresponding dithioacetals 4 in high yields （up to 91%） in the presence of 2a. Moreover, 2a showed high chemoselectivity between aldehyde and ketone in thioacetalization.     

Palladium‐Catalyzed Asymmetric Aminohydroxylation of 1,3‐Dienes

A Pd^II‐catalyzed asymmetric aminohydroxylation of 1,3‐dienes with N‐tosyl‐2‐aminophenols was developed by making use of a chiral pyridinebis(oxazoline) ligand. The highly regioselective reaction provides direct and efficient access to chiral 3,4‐dihydro‐2H‐1,4‐benzoxazines in high yield and enantioselectivity (up to 96:4 e.r.). The reaction employs readily available N‐tosyl‐2‐aminophenols as a unique aminohydroxylation reagent and is complementary to known asymmetric aminohydroxylation methods.     

Palladium‐catalyzed three‐component cyclization of 2‐bromocyclohex‐1‐enecarboxylic acids with carbon monoxide and arylhydrazines leading to 2‐anilinohydroisoindoline‐1,3‐diones

2‐Bromocyclohex‐1‐enecarboxylic acids are carbonylatively cyclized with arylhydrazines or their hydrochlorides in tetrahydrofuran at 120 °C under carbon monoxide pressure in the presence of a catalytic amount of PdCl₂ and 1,3‐bis(diphenylphosphino)propane along with Et₃N to give 2‐anilinohydroisoindoline‐1,3‐diones. Copyright © 2015 John Wiley & Sons, Ltd.     

Reaction of tellurium tetraiodide with 2,3‐dihydro‐1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene

2,3‐Dihydro‐1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene 1 (Carb, R¹ = ⁱPr, R² = Me) reacts with TeI₄ to give the carbene adduct CarbTeI₂ ( 3 ). The crystal structure of 3 consists of T‐shaped monomeric fragments linked by weak Te. I interactions to form infinite helical chains. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:316–319, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20090