The formation of a metallacycloheptadienyl intermediate in the reaction of palladacyclopentadienyl derivatives with tetracyanoethylene

The palladium(II) derivatives of the type 1 [Pd(LL′)(C₄R₁R₂R₃R₄)] (LL′ = HNSPh:2-(phenylthiomethyl)-pyridine (A), BiPy: 2,2′-bipyridyl (B), DPPE: bis-diphenylphosphinoethane (C), NEOC: neocuproine (2,2′-dimethyl-o-phenanthroline) (D), R₁ = R₄ = COOMe, R₂, R₃ = C₁₀H₆ (a), R₁ = R₃ = C₆H₅, R₂ = R₄ = COOMe (b), R₁ = R₂ = R₃ = R₄ = COOMe (c)) react with the electron poor olefin tetracyanoethylene (TCNE) to yield under mild conditions the type 2 cycles C₆(CN)₄R₁R₂R₃R₄ and the corresponding palladium(0) olefin derivative [Pd(η²]-TCNE)(LL′)]. The olefin insertion reactions are usually fast, but in the case of the reaction of complex 1Da with TCNE accumulation of an intermediate is observed. The low temperature NOESY spectrum allows the determination of the intermediate structure which can be described as a hepta-membered metallacycle species.     

The synthesis of oligoether-substituted benzimidazolium bromides and their use as ligand precursors for the Pd-catalyzed Heck coupling in water

The oligoether-substituted (CH₃(OCH₂CH₂)_n-; n = 1, 2 or 3) benzimidazolium bromides (3-7) and oligoether-linked (-CH₂(CH₂OCH₂)_nCH₂-, n = 1, 2 or 3) bisbenzimidazolium dibromides (8-13) were prepared by quarternization of N-substituted benzimidazoles (1 and 2) with the bulky benzyl bromides (ArCH₂Br: Ar = C₆H₂(CH₃)₃-2,4,6 and C₆(CH₃)₅). trans-Bis(carbene) palladium(II) complexes 14 and 15 derived from 4 and 6 were synthesized by using Ag complexes as carbene-transfer agents in dichloromethane at ambient temperature. In addition, the reactions of 4 and 6 with Pd(OAc)₂ and NaBr gave the Pd(II) dimers 16 and 17 which can readily be cleaved by triphenylphosphine to afford the benzannulated monocarbene (NHC) monophosphine Pd(II) complexes [PdBr₂(NHC)(PPh₃)] (18 and 19). All compounds have been fully characterized by using elemental analysis, ¹H, ¹³C and ³¹P NMR spectroscopies. X-ray diffraction studies on single crystals of 19a and 19b confirm the cis square planar geometry. In situ formed complexes from Pd(OAc)₂ and benzimidazolium salts (3-13) and preformed Pd(II) complexes 14, 15, 18 and 19 were tested as catalyst for the Heck coupling reaction in water. The influence of the oligoether and benzyl substituents on N atoms and CH₃-substituents on the 5,6-positions of benzimidazole frame were investigated under the same conditions in the Heck coupling reaction. In situ formed catalysts showed better conversions than the isolated Pd(II) complexes. The length of the oligoether spacer significantly increases the activity. The salts with two benzimidazole moieties connected by an oligoether as the spacer 8-13 showed similar catalytic activities in the Heck coupling reaction with the mono salts 3-7 bearing corresponding oligoethers on the N atom.     

NBS as an efficient catalyst for the synthesis of 1,5-benzodiazepine derivatives under mild conditions

Various biologically important 1,5-benzodiazepine derivatives were efficiently synthesized in excellent yields using catalytic amounts of NBS (10 mol %). This inexpensive, nontoxic, and readily available catalyst efficiently catalyzes the condensation of several aromatic as well as aliphatic ketones with substituted o-phenylenediamines.     

Convenient preparation of (η-alkadiene)dichloroplatinum(II) complexes from [PtCl6] anions and their reduction to platinum(0) alkene complexes under phase-transfer catalysis conditions

Convenient one-pot reduction-complexation reactions of hexachloroplatinato(IV) anions to (η⁴-alkadiene)dichloroplatinum(II) complexes (η⁴-alkadiene = COD, DAE, DCPD, NBD) under suitable phase-transfer catalysis conditions are reported. Reduction to zerovalent platinum alkene complexes has been obtained in the presence of an excess of alkene, potassium formate and 18-crown-6 as phase-transfer catalyst (alkene = COD, NB, dba). The crystal and molecular structure of [Pt_1.03(dba)₃]·CH₂Cl₂ has been studied by X-ray diffraction methods: it can be described as a solid solution of Pt(dba)₃ and Pt₂(dba)₃, the mononuclear complex being largely prevailing.     

A new, mild one-pot synthesis of iodinated heterocycles as suitable precursors for N-heterocyclic carbene complexes

The use of I₂/AgOAc in dichloromethane constitutes a cheap, mild, and efficient method for the selective iodination of a variety of heterocycles. In a number of cases, this method provides superior yields to other literature methods and affords iodo-functionalized heterocycles that are suitable precursors for carbene complexes.     

Highly rapid and direct synthesis of monoacylated piperazine derivatives from carboxylic acids under mild conditions

A series of monoacylated piperazine derivatives were obtained by the reaction of carboxylic acids with 2-chloro-4,6-dimethoxy-1,3,5-triazine in dichloromethane at room temperature. Good to excellent yields, short reaction times and mild reaction conditions are important features of this methodology.     

A highly active catalyst for the reductive cyclization of ortho-nitrostyrenes under mild conditions

A mild and efficient method for the palladium-catalyzed reductive cyclization of ortho-nitrostyrenes to afford indoles is reported. Treatment of ortho-nitrostyrenes with 0.1 mol% palladium (II) trifluoroacetate [Pd(TFA)₂] and 0.7 mol% 3,4,7,8-tetramethyl-1,10-phenanthroline (tm-phen) in DMF at 15 psig CO and 80 °C afforded indoles in good to excellent yields. When the reaction was conducted in toluene, the corresponding N-hydroxyindole was isolated. A mechanism that accounts for the formation of N-hydroxyindole is proposed.     

A highly efficient Pd-C catalytic hydrogenation of pyridine nucleus under mild conditions

A synergistic Pd-C catalytic hydrogenation of 4-pyridinecarboxamides straightforward to 4-piperidinecarboxamide hydrochlorides was developed in the presence of ClCH₂CHCl₂. It provided a novel strategy for highly efficient hydrogenation of pyridine nuclear by using low-cost Pd-C catalyst under mild conditions.     

Ruthenium(Ⅲ) chloride as an efficient catalyst for the synthesis of perimidine derivatives under mild conditions

Various biologically important perimidine derivatives have been synthesized efficiently from various ketones and naphthalene1,8-diamine by using a catalytic amount of RuC13 (1 mol%). This method is a very simple and high yielding reaction for the synthesis of perimidine derivatives.     

Synthesis of polyamides from rigid and sterically hindered dicarboxylic acids and diamines under mild conditions

The rate of polycondensation of piperazine with the 2,4-dinitrophenyl, succinimido, phthalimido, and 4-nitrophenyl esters of bicyclo[2.2.2]octane-trans-2,3-dicarboxylic acid was measured and found to decrease in this sequence. In the reaction of two moles of piperazine with one mole of diester, the reactivity of both ester groups was equal. In equimolar mixtures, the second ester group reacts with the second group about ten times slower because of steric hindrance. In the reaction of the esters with N,N′-dimethylethylenediamine no such effects were observed. The aminolysis of the N-hydroxyphthalimido ester stops at low conversions unless a very large excess of triethylamine is added. The catalytic effect of 1,2,4-triazole on the aminolysis was proportional to the triazole concentration. From the rate of ester consumption in the presence of pure triethylamine, the extent of possible racemization of the optically active dicarboxylic acid was estimated. In view of the rate data, the extent of polycondensation, and side reactions, only 2,4-dinitrophenyl and N-hydroxysuccinimido diesters are suitable for the synthesis of polyamides derived from rigid and sterically hindered dicarboxylic acids.     

Stereoselective synthesis of substituted 1,2-ethylenediaziridines and their use as ligands in palladium-catalyzed asymmetric allylic alkylation

The double addition of organometallic reagents to fused oxazino-oxazines prepared from glyoxal and (S)-phenylglycinol afforded C₂- or C₁-symmetric 1,2-ethylenebis(β-aminoalcohols), depending on the nature of the organometallic reagent. This route was modified by the use of (S)-valinol and phenylglyoxal as starting materials, and by reduction of the oxazino-oxazines by diborane. Cyclization of the β-aminoalcohol moieties gave 1,2-ethylenediaziridines bearing one substituent/stereocenter on the ring carbon and one, two or no substituents/stereocenters in the ethylene tether. These bis(aziridines) were used as ligands in the Pd-catalyzed allylic alkylation of dimethyl malonate. It was established that the substituent(s) in the carbon tether and the configuration of the corresponding stereocenters have limited influence on the enantioselectivity.     

Palladium-catalysed reactions of 6-halogeno-1,1′-binaphthyl derivatives. A detailed investigation of structure/reactivity and structure/selectivity relationships

Five 6-halogeno-binaphthyl derivatives of different structure were synthesised starting from 2,2′-dihydroxy-1,1′-binaphthyl 1. Several new 6-substituted binaphthyl compounds were obtained via the palladium-catalysed reactions of these derivatives. The reactivity of 6-iodo derivatives was much greater in most cases. In cross-coupling reactions the 6-bromo compounds were converted into the products using longer reaction times and/or higher temperatures. The reactivity difference between the two types of substrates was especially marked in aminocarbonylation and Heck reactions.     

A mild and simple synthesis of N-aryl substituted toluenesulfamides under solvent-free conditions

N- aryl substituted benzenesulfamides are often used as heating-sensitive recording material1, thermal printing material2, sensitizer3 and developer4. Moreover, some of the benzenesulfamides have antifungal activities5. Many methods have been described for preparation of sulfamides. They are used to carry out in solvent8 or in solid phase condition9. These methods required solvent or solid support and even required heating or cooling. At the same time, the process of these methods is complex. Now we have developed a new method to prepare N-aryl substituted toluenesulfamides under solvent-free conditions.In recent years, solvent-free technology has gained popularity in organic synthesis. For instance,solidstate reaction and microwave reaction have received considerable attention. Solvent-free synthesis of amides has been reported10-11. This technology has many advantages such as high efficiency and selectivity, easy separation and environmental acceptability. All these merits are in accord with green chemistry's requirements of energy-saving, high efficiency and environmental benefits.In our paper, we used a simple and efficient method for preparing N-aryl substituted toluenesulfamides under solvent-free conditions, as a replacement for classic solvent, which gives many environmental benefits.All reactions were completed at room temperature by co-grinding in an agate mortar for 3-20min and the results are shown in Table 1.In conclusion, we have developed an efficient and convenient method of preparation N-aryl substituted toluenesulfamides in high yields. It symbols an improvement for synthesis of benzenesulfamides.     

温和条件下丁二酰亚胺-N-磺酸催化合成双吲哚甲烷和香豆素衍生物(英文)

A mild and simple procedure is described for the synthesis of bis(indolyl)methane and coumarin derivatives using succinimide-N-sulfonic acid as an efficient,cheap,and reusable catalyst under mild conditions.     

A microwave-assisted, copper-catalyzed three-component synthesis of dihydropyrimidinones under mild conditions

The synthesis of dihydropyrimidinones via a clean multi-component Biginelli reaction under microwave irradiation is reported. The copper-catalyzed process proved to be simple, efficient, economical, and environmentally friendly.     

HypoGel负载Pd纳米催化剂制备与表征及温和条件下催化Suzuki反应(英文)

A new heterogeneous catalyst composed of Pd nanoparticles immobilized within a HypoG el resin has been prepared in the absence of any ligands using an extensive cross-linking method.This newly developed nanocatalyst was characterized by N_2 adsorption-desorption,X-ray diffraction(XRD),transmission electron microscopy(TEM),scanning electron microscopy(SEM),energy dispersive X-ray(EDX),Fourier transform infrared spectroscopy and inductively coupled plasma-mass spectrometer(ICP-MS)techniques.TEM and XRD results revealed that the Pd nanoparticles were well dispersed with diameters in the range of 4–12 nm,and an average size of about 8 nm.The cross-linked Pd catalyst demonstrated excellent catalytic activity towards the synthesis of a series of biaryl compounds by the reaction of various aryl halides(e.g.,bromides andiodides)with phenylboronic acid in the presence of tetrabutylammonium bromide.ICP-MS analysis indicated that there was only 0.25%weight loss of Pd(0.55±0.02 ppm)from the supported catalyst after the first cycle reaction.Furthermore,the catalyst showed excellent reusability(up to five uses)with consistently high levels of catalytic activity following its recovery by filtration.     

Stereoselective synthesis of oxazolidines from 2-amino-2-deoxy-d-allose derivatives and their reactivity with nucleophiles

The use of 2-amino-2-deoxy-d-allose in the synthesis of oxazolidines is described. The reaction takes place with total stereoselectivity in the preparation of both simple oxazolidines (from aldehydes as reagent) and bicyclic oxazolidines (from chlorocarbonyl compounds and keto-acids as reagents). The reactivity of the obtained oxazolidines with hydride and alkylmagnesium chlorides is also described.