Simple amine/Pd(OAc)(2)-catalyzed suzuki coupling reactions of aryl bromides under mild aerobic conditions

A new palladium catalyst (DAPCy) made from Pd(OAc)(2) and commercially available, inexpensive dicyclohexylamine has been developed for the Suzuki coupling reaction of aryl bromides with boronic acids to give the coupling products in good to high yields. The air-stable catalyst was characterized and well-defined by X-ray crystallography. A catalytic system involving DAPCy in dioxane demonstrates a temperature-dependent reactivity toward aryl bromides with different electronic substituents, and selectively couples electron-deficient aryl bromides with boronic acids over electron-rich ones at room temperature. Another catalytic system employing DAPCy in EtOH provides a general and convenient method to prepare biaryls from aryl bromides and boronic acids with a broad range of functional groups at room temperature and under aerobic conditions.     

Gold(I)-catalyzed direct C-H arylation of pyrazine and pyridine with aryl bromides

An efficient procedure for the direct C-H arylation of electron-poor aromatics such as pyrazine and pyridine with aryl bomides is described. In the presence of catalytic amount of Cy₃PAuCl and with the use of t-BuOK as base, pyrazine undergoes the direct C-H arylation with aryl bromides at 100 °C, and the yields of the arylated products depend on the nature of aryl bromides. In the cases of electron-rich aryl bromides used, the arylated pyrazines can be obtained in good to high yields. For electron-poor aryl bromides, the addition of AgBF₄ is the crucial point to accelerate the coupling reaction to give the arylated products in moderate yields. Pyridine also reacts with electron-rich aryl bromides catalyzed by Cy₃PAuCl to give a mixture of arylated regioisomers in moderate yield. However, in order to realize the direct C-H arylation of pyridine with electron-poor aryl bromides, the addition of silver salt as additive and a milder reaction temperature (60 °C) are required.     

Rapid Synthesis of Glycosyl Bromides by Ultrasound Irradiation

A convenient and environmentally friendly reactor for the synthesis of glycosyl bromides via ultrasound irradiation was designed. Peracetylated glycosyl bromides were synthesized from free saccharides by means of a one-pot method. Benzoylated and 6-subsituted glycosyl bromides were prepared from protected saccharides. The glycosyl bromides were obtained in isolated yields of 83% to 96%.     

Ligand-Controlled Nickel-Catalyzed Regiodivergent Cross-Electrophile Alkyl-Alkyl Couplings of Alkyl Halides

Functionalizing specific positions on a saturated alkyl molecule is a key challenge in synthetic chemistry. Herein, a ligand-controlled regiodivergent alkylations of alkyl bromides at different positions by Ni-catalyzed alkyl-alkyl cross-electrophile coupling with the second alkyl bromides has been developed. The reaction undergoes site-selective isomerization on one alkyl bromides in a controlled manner, providing switchable access to diverse alkylated structures at different sites of alkyl bromides. The reaction occurs at three similar positions with excellent chemo- and regioselectivity, representing a remarkable ligand tuned reactivity between alkyl-alkyl cross-coupling and nickel migration along the hydrocarbon side chain. This reaction offers a catalytic platform to diverse saturated architectures by alkyl-alkyl bond-formation from identical starting materials.     

Conversion of Alcohols to Bromides by Trimethylsilane and lithium Bromide in Acetone

Conversion of alcohols to alkyl bromides is one of the most frequently used functional group transformation reactions. Phosphorus tribromide is one of the most popular classical reagents. Triphenylphosphine has been used in combination with bromine,carbon tetrabromide,N-halo imides and other bromide compounds as a mild reagents for the preparation of alkyl bromides. More reacently, halotrimethylsilanes were found to be useful for halogenation of alcohols. Geo- rge A.Olah successfully convert…     

Synthesis of unsymmetrical aroyl acyl imides by aminocarbonylation of aryl bromides.

Aroyl imides were prepared by a palladium-catalyzed aminocarbonylation reaction of aryl bromides with carbon monoxide and primary amides in good yields (58-72%). The reactions were carried out under mild conditions (5 bar, 120 degrees C) using 1 mol % of a palladium phosphine complex. Several aryl bromides were reacted with formamide, acetamide, benzamide, and benzenesulfonamide, respectively. For activated aryl bromides, a phosphine-to-palladium ratio of 2:1 was sufficient, but less reactive aryl bromides required a ligand-to-palladium ratio of 6:1 in order to stabilize the catalyst and achieve full conversion. The imides were very sensitive to aqueous basic conditions and were easily converted to aroyl amides or benzoic acids.     

Per-6-amino-beta-cyclodextrin as an efficient supramolecular ligand and host for Cu(I)-catalyzed N-arylation of imidazole with aryl bromides

Per-6-amino-beta-cyclodextrin (per-6-ABCD), acting simultaneously as a supramolecular ligand for CuI and host for aryl bromides, catalyzes N-arylation of imidazole with aryl bromides under mild conditions. This simple method proceeds with excellent yield for the coupling of imidazole with various substituted aryl bromides demonstrating good tolerance of other functionalities.     

The complexometric determination of bromides and bromates in the presence of each other

Summary A complexometric titration method is described for the determination of bromides and bromates in the presence of each other. Bromides are precipitated as silver bromide, the precipitate dissolved in a solution of potassium tetracyanoniccolate and the displaced nickel titrated by means of a EDTA solution. Bromine is determined indirectly: two atoms of bromine correspond to one of nickel. The bromates are reduced to bromides and the sum of the bromides are determined by the described method. The difference of burette readings gives the bromides obtained by reduction of bromates. The method gives good results with mixtures of bromides and bromates in the ratio of 1 20 and vice versa.     

Facile preparation of organozinc bromides using electrogenerated highly reactive zinc and its use in cross-coupling reaction

Highly reactive zinc was readily prepared by electrolysis of a DMF solution containing pyrene as a mediator with a platinum cathode and a zinc anode. Preferential reduction of pyrene occurred to generate the corresponding radical anion, which reduced zinc ions generated from anodic dissolution to give zero valent zinc with high reactivity. The reactive zinc was successfully used for an efficient transformation of bromoalkanes into the corresponding organozinc bromides. Organozinc bromides obtained were further used successfully in Pd-catalyzed cross-coupling reaction with various aryl iodides and bromides.     

环钯化二茂铁亚胺-三苯基膦配合物的合成、表征及催化Suzuki反应研究

为筛选高效催化Suzuki反应的催化剂, 合成了3种新的环钯化二茂铁亚胺-三苯基膦配合物2~4, 经元素分析(或HRMS)、 红外光谱和核磁共振谱对其结构进行了表征, 并通过X射线单晶衍射测定了化合物3的晶体结构. 这些化合物容易合成, 在空气和溶液中稳定, 可用作芳基溴及杂芳基溴与苯基硼酸偶联的Suzuki反应催化剂. 使用摩尔分数为0.01%的催化剂3, 以2倍量的K3PO4为碱, 于110 ℃下, 在甲苯中反应5~15 h, 使具有不同电子和位阻效应的取代芳基溴及杂芳基溴能以较高的产率与苯基硼酸反应生成偶联产物; 与溴苯相比, 带吸电子基的溴苯反应活性较高, 催化剂的摩尔分数降低至0.001%时, 仍能得到较高产率, 而带强给电子基的溴苯如4-溴苯甲醚及带邻位取代基的溴苯在其它条件相同时, 需要延长反应时间才能得到较高的产率.     

Hydrophobic hydration of some different types of quaternary ammonium bromides in mixtures of water andN,N-dimethylformamide

Enthalpies of solution of methyltributylammonium bromide, tetraethanolammonium bromide, and three azoniaspiroalkane bromides in binary solvent mixtures of water and N,N-dimethylformamide have been measured calorimetrically at 298.15^oK over the whole mole fraction range. The results are interpreted in terms of a simple hydration model with two parameters and compared with those of the corresponding tetraalkylammonium bromides. Enthalpic studies with different types of quaternary ammonium bromides are useful in reexamining the assumptions and limitations of the hydration model.     

Nickel-catalyzed reductive coupling of aryl halides with secondary alkyl bromides and allylic acetate

A room-temperature Ni-catalyzed reductive method for the coupling of aryl bromides with secondary alkyl bromides has been developed, providing C(sp(2))-C(sp(3)) products in good to excellent yields. Slight modification of this protocol allows efficient coupling of activated aryl chlorides with cyclohexyl bromide and aryl bromides with allylic acetate.     

A novel tunable aromatic bromination method using alkyl bromides and sodium hydride in DMSO

Aromatic bromination on various aromatic systems with different substitutions was performed in the presence of alkyl bromide and sodium hydride in DMSO. Mono-bromination on a wide range of substrates was achieved by selecting proper alkyl bromides and controlling its amount. Further bromination could happen with more active alkyl bromides and additional amount of bromides and sodium hydride. The yields ranged from moderate to excellent. In addition, reaction mechanism was postulated to explain our observations.     

Hydration structures of bromides on cationic micelles

The peripheral structures of bromides on dodecyltrimethylammonium bromide (DTAB) and hexadecyltrimethylammonium bromide (HTAB) micelles have been studied by X-ray absorption fine structure (XAFS) at the Br-K edge. The XAFS spectra indicate that water is a dominant scattering group for Br- even in these micellar solutions. However, the oscillation intensity decreases with increasing micellar concentration, suggesting that the bromides are dehydrated to some extent when they are bound to the micelles. A XAFS analysis routine gives unusually short Br-O (water) distances and is inapplicable to the present systems. This comes from the structure of the first coordination shell, in which two or more scattering paths are involved. The second scattering group is obviously the head group of the surfactants forming the micelles. The detailed analysis has allowed us to estimate the hydration number of the bromides bound on the DTAB and HTAB micelles (N = ca. 4.2). The assumption that all of the bromides form direct ion-associates with the head groups causes the contradiction to the results of the XAFS analyses. This strongly implies that some of the bromides partitioned into the micelle are completely hydrated as far as their first coordination shell is concerned. Assuming that the maximum hydration number of the bromides bound to the head groups of the micelle is three, 40% of the bromides partitioned into the micelle are completely hydrated.     

The effect of unsaturation on the reaction of aqueous alkyl bromides with brass foil

Brass (a zinc/copper alloy) foil reacts with mixtures of water and alkyl bromides to give dissolution of zinc and copper. The relative rates of leaching depend on the bromide used: saturated bromides favor dissolution of zinc, whereas unsaturated bromides favor dissolution of copper. This difference is attributed to the formation of π-complexes between the unsaturated linkages and the copper atoms.     

An Improved Direct Oxidation of Alkyl Halides to Aldehydes

The oxidation of alkyl chlorides and bromides with dimethyl sulfoxide has been performed in the presence of sodium iodide. This method allows a convenient one-step procedure for the preparation of aldehydes from alkyl chlorides and bromides.     

Polarography of polyhalogen-substituted benzyl bromides and the corresponding benzylmercuric bromides

Conclusions On the basis of a comparison of the polarographic behavior of a series of polybromine-substituted benzylmercuric bromides and the corresponding substituted benzyl bromides it was shown in the case of benzyl bromides active in the preparative reaction with metallic mercury that the reduction takes place through the initial formation of organomercury compounds at the surface of the mercury electrode.Translated from Izvestiya Akademii Nauk SSSR. Seriya Khimicheskaya, No. 3, pp. 546–548, March, 1985.     

Phosphine-free palladium-catalysed direct 5-arylation of imidazole derivatives at low catalyst loading

The regioselective 5-arylation of imidazole derivatives with aryl bromides using a low loading of a phosphine-free palladium catalyst gives a simple and economic access to the corresponding 5-arylimidazoles. The choice of the base and of the solvent was found to be crucial to form these products in high yields. Using KOAc as the base, DMAc as the solvent and only 0.5-0.01 mol % Pd(OAc)₂ as the catalyst, the target products were obtained in moderate to good yields with a wide variety of aryl bromides. Substituents such as fluoro, trifluoromethyl, formyl, acetyl, propionyl, ester or nitrile on the aryl bromide are tolerated. Sterically congested aryl bromides or heteroaryl bromides can also be employed. The nature of the substituents on the imidazole derivative has an important influence on the yields.     

Efficient Radical Coupling of Organobromides Using Dimanganese Decacarbonyl

Wurtz-type radical coupling of a variety of allylic and benzylic bromides was observed on irradiation with dimanganese decacarbonyl in excellent yield (77-99%). Efficient cross-coupling of two different bromides was also readily achieved.     

Indium(I) iodide promoted cleavage of diphenyl diselenide and disulfide and subsequent palladium(0)-catalyzed condensation with vinylic bromides. A simple one-pot synthesis of vinylic selenides and sulfides

[reaction: see text] Diphenyl diselenide (and disulfide) undergo facile reaction with indium(I) iodide and the corresponding intermediate complex condenses in situ with a variety of substituted vinyl bromides in the presence of a catalytic amount of tetrakis(triphenylphosphine)palladium(0) [Pd(PPh3)4] in THF at room temperature to produce vinylic selenides and sulfides in good yields. The conversion of (E)-vinyl bromides is remarkably stereoselective giving (E)-vinyl selenides (and sulpfides) whereas the stereoselectivity in reaction of (Z)-vinyl bromides is not very good.