Facile synthesis of beta-organotellurobutenolides via electrophilic tellurolactonization of alpha-allenoic acids

We report a convenient and highly efficient method for the synthesis of beta-organotellurobutenolides by the aryltellurenyl halides-induced electrophilic tellurolactonization of alpha-allenoic acids under mild conditions. The resulting beta-organotellurobutenolides can be utilized as precursors for versatile butenolide derivatives through a substitution reaction with organocuprate reagent or Pd/Cu(I)-catalyzed cross-coupling with terminal alkyne.     

Asymmetric allylic alkylation of acyclic allylic ethers with organolithium reagents

A highly efficient, regio- and enantioselective Cu(I) /phosphoramidite-catalyzed asymmetric allylic alkylation of allyl ethers with organolithium reagents is reported. The use of organolithium reagents is essential for this catalytic C?C bond formation due to their compatibility with different Lewis acids. The versatility of allylic ethers under the copper-catalyzed reaction conditions with organolithium reagents is demonstrated in the shortest synthesis of (S)-Arundic acid.     

Studies of Electrode Reactions and Coordination Geometries of Cu(I) and Cu(II) Complexes with Bicinchoninic Acid

Bicinchoninic acid (BCA) is widely used for determining the valence state of copper in biological systems and quantification of the total protein concentration (BCA assay). Despite its well‐known high selectivity of Cu(I) over Cu(II), the exact formation constants for Cu(I)(BCA)₂³⁻ and Cu(II)(BCA)₂²⁻ complexes remain uncertain. These uncertainties, affect the correct interpretations of the roles of copper in biological processes and the BCA assay data. By studying the voltammetric behaviors of Cu(I)(BCA)₂³⁻ and Cu(II)(BCA)₂²⁻, we demonstrate that the apparent lack of redox reaction reversibility is caused by an adsorption wave of Cu(II)(BCA)₂²⁻. With the adsorption wave identified, we found that the Cu(I)/Cu(II) selectivity of BCA is essentially identical to another popular ligand, bathocuproinedisulfonic acid (BCS). Density functional theory calculation on the geometries of Cu(I)(BCA)₂³⁻ and Cu(II)(BCA)₂²⁻ rationalizes the preferential Cu(I) binding by BCA and the strong adsorption of the Cu(II)(BCA)₂²⁻ complex at the glassy carbon electrode. Based on the shift in the standard reduction potential of free Cu(II)/Cu(I) upon binding to BCA, we affirm that the formation constants for Cu(I)(BCA)₂³⁻ and Cu(II)(BCA)₂²⁻ are 10^17.2 and 10^8.9, respectively. Therefore, BCA can be chosen among various ligands for effective and reliable studies of the copper binding affinities of different biomolecules.     

Cyclopalladated Ferrocenylimine: Highly Active Catalyst for the Suzuki Reaction of Aryliodides with Phenylboronic Acid

Transition-metal catalyzed reaction represents an extremely versatile method in organic synthesis. [1] Searching for highly efficient catalysts has been the aim of organic chemists. Palladium catalyzed coupling of aryl halides with arylboronic acids, Suzuki reaction, is one of the most powerful methods for carbon-carbon bond formation. [2] Here we report the high efficiency of cyclopalladated ferrocenylimine 1 for the Suzuki coupling reaction of aryl iodides with phenylboronic acid. Excellent yields and high turnover numbers were obtained under optimized conditions after repeated uses (Schemes 1, 2).     

Alkyl- and aryl-substituted corroles. 5. Synthesis, physicochemical properties, and X-ray structural characterization of copper biscorroles and porphyrin-corrole dyads

The synthesis and characterization of cofacial copper biscorroles and porphyrin-corroles linked by a biphenylenyl or anthracenyl spacer are described. The investigated compounds are represented as (BCA)Cu(2) and (BCB)Cu(2) in the case of the biscorrole (BC) derivatives and (PCA)Cu(2) and (PCB)Cu(2) in the case of porphyrin (P)-corrole (C) dyads, where A and B represent the anthracenyl and biphenylenyl bridges, respectively. A related monomeric corrole (Me(4)Ph(5)Cor)Cu and monomeric porphyrin (Me(2)Et(6)PhP)Cu that comprise the two halves of the porphyrin-corrole dyads were also studied. Electron spin resonance (ESR), (1)H NMR, and magnetic measurements data demonstrate that the copper corrole macrocycle, when linked to another copper corrole or copper(II) porphyrin, can be considered to be a Cu(III) complex in equilibrium with a Cu(II) radical species, copper(III) corrole being the main oxidation state of the corrole species at all temperatures. The cofacial orientation of (BCB)Cu(2), (BCA)Cu(2), and (PCB)Cu(2) was confirmed by X-ray crystallography. Structural data: (BCB)Cu(2)(C(110)H(82)N(8)Cu(2).3CDCl(3)), triclinic, space group P, a = 10.2550(2) A, b = 16.3890(3) A, c = 29.7910(8) A, alpha = 74.792(1) degrees , beta = 81.681(1) degrees , gamma = 72.504(2) degrees , Z = 2; (BCA)Cu(2)(C(112)H(84)N(8)Cu(2).C(7)H(8).1.5H(2)O), monoclinic, space group P 2(1)/c, a = 16.0870(4) A, b = 35.109(2) A, c = 19.1390(8) A, beta = 95.183(3) degrees , Z = 4; (PCB)Cu(2)(C(89)H(71)N(8)Cu(2).CHCl(3)), monoclinic, space group P2(1)/n, a = 16.7071(3) A, b = 10.6719(2) A, c = 40.8555(8) A, beta = 100.870(1) degrees , Z = 4. The two cofacial biscorroles, (BCA)Cu(2) and (BCB)Cu(2), both show three electrooxidations under the same solution conditions. The reduction of (BCA)Cu(2) involves a reversible electron addition to each macrocycle at the same potential of E(1/2) = -0.20 V although (BCB)Cu(2) is reversibly reduced in two steps to give first [(BCB)Cu(2)](-) and then [(BCB)Cu(2)](2)(-), each of which was characterized by ESR spectroscopy as containing a Cu(II) center. These latter electrode reactions occur at E(1/2) = -0.36 and -0.51 V versus a saturated calomel reference electrode. The half-reduced and fully reduced (BCB)Cu(2) show similar Cu(II) ESR spectra, and no evidence of a triplet signal is observed. The two well-separated reductions of (BCB)Cu(2) to give [(BCB)Cu(2)](2)(-) can be attributed to a stronger pi-pi interaction between the two macrocycles of this dimer as compared to those of (BCA)Cu(2). The copper porphyrin-corrole dyads, (PCA)Cu(2) and (PCB)Cu(2), show five reversible oxidations and two reversible reductions, and these potentials are compared with corresponding values for electrochemical reactions of the porphyrin and corrole monomers under the same solution conditions.     

A new copper(II) complex as an efficient catalyst of luminol chemiluminescence

A new copper complex (2) has exhibited highly efficient catalytic activity of luminol chemiluminescence in water in the presence of ascorbic acid and dissolved O2 under conditions that conventional catalysts such as Cu(OAc)2, hemin or cyclen-Cu(II) did not show significant activity.     

Spectrophotometric total protein assay with copper(II)-neocuproine reagent in alkaline medium

Total protein assay was made using copper(II)–neocuproine (Nc) reagent in alkaline medium (with the help of a hydroxide-carbonate-tartarate solution) after 30 min incubation at 40 °C. The absorbance of the reduction product, Cu(I)–Nc complex, was recorded at 450 nm against a reagent blank. The absorptivity of the developed method for bovine serum albumin (BSA) was 0.023 l mg⁻¹ cm⁻¹, greater than that of Lowry assay (0.0098), and much greater than that of Cu(II)–bicinchoninic acid (BCA) assay (0.00077). The linear range of the developed method (8–100 mg l⁻¹ BSA) was as wide as that of Lowry, and much wider than that of BCA (200–1000 mg l⁻¹ BSA) assay. The sensitivity of the method was greater than those of Cu-based assays (biuret, Lowry, and BCA) with a LOD of 1 mg l⁻¹ BSA. The within-run and between-run precisions as RSD were 0.73 and 1.01%, respectively. The selectivity of the proposed method for protein was much higher than those of dye-binding and Lowry assays: Most common interferents to other protein assays such as tris, ethanolamine, deoxycholate, CsCl, citrate, and triton X-100 were tolerated at 100-fold concentrations in the analysis of 10 mg l⁻¹ BSA, while the tolerance limits for other interferents, e.g., (NH₄)₂SO₄ and acetylsalicylic acid (50-fold), SDS (25-fold), and glycerol (20-fold) were at acceptable levels. The redox reaction of Cu(II)–Nc as an outer-sphere electron transfer agent with the peptide bond and with four amino acid residues (cystine, cysteine, tryptophan, and tyrosine) was kinetically more favourable than that of Cu(II) alone in the biuret assay. Since the reduction product of Cu(II) with protein, i.e., Cu(I), was coordinatively saturated with Nc in the stable Cu(Nc)₂⁺ chelate, re-oxidation of the formed Cu(I) with Fenton-like reactions was not possible, thereby preventing a loss of chromophore. After conventional protein extraction, precipitation, and redissolution procedures, the protein contents of the minced meat (veal and turkey), sardine, various milk products, and egg white were analyzed with the proposed and Lowry methods, and the results correlated appreciably (r = 0.98). The method was validated by Kjeldahl analyses of the tested samples; the data sets of complex samples assayed by Cu(II)–Nc and Lowry correlated to the findings of Kjeldahl yielded correlation coefficients r = 0.96 and 0.97, respectively, with slopes being close to 1. Interferences of glucose and thiol compounds at relatively low concentrations could be compensated for by selecting a lower alkaline pH (i.e., pH 10) at a cost of slightly reduced sensitivity and adding an identical amount of interferent to the reagent blank, respectively, since the absorbances due to BSA and interferent were additive. Thus a novel spectrophotometric method for total protein assay using a stable reagent and chromophore, which was simple, rapid, sensitive, flexible, and relatively selective, was developed, and applied to a variety of food products.     

Synthesis of Aryldiazoacetates through Palladium(0)‐Catalyzed Deacylative Cross‐Coupling of Aryl Iodides with Acyldiazoacetates

Palladium(0)‐catalyzed deacylative cross‐coupling of aryl iodides and acyldiazocarbonyl compounds can be achieved at room temperature under mild reaction conditions. The coupling reaction represents a highly efficient and general method for the synthesis of aryldiazocarbonyl compounds, which have found wide and increasing applications as precursors for generating donor/acceptor‐substituted metallocarbenes.     

Precisely Designed Isopeptide Bridge‐Crosslinking Endows Artificial Hydrolases with High Stability and Catalytic Activity under Extreme Denaturing Conditions

Enzymes normally lose their activities under extreme conditions due to the dissociation of their active tertiary structure. If an enzyme could maintain its catalytic activity under non‐physiological or denaturing conditions, it might be used in more applications in the pharmaceutical and chemical industries. Recently, we reported a coiled‐coil six‐helical bundle (6HB) structure as a scaffold for designing artificial hydrolytic enzymes. Here, intermolecular isopeptide bonds were incorporated to enhance the stability and activity of such biomolecules under denaturing conditions. These isopeptide bridge‐tethered 6HB enzymes showed exceptional stability against unfolding and retained or even had increased catalytic activity for a model hydrolysis reaction under thermal and chemical denaturing conditions. Thus, isopeptide bond‐tethering represents an efficient route to construct ultrastable artificial hydrolases, with promising potential to maintain biocatalysis under extreme conditions.     

Highly efficient synthesis of azabicyclo[x.y.0]alkane amino acids and congeners by means of Rh-catalyzed cyclohydrocarbonylation

A highly efficient method for the synthesis of 1-azabicyclo[x.y.0]alkane amino acid derivatives and their congeners by means of extremely regioselective cyclohydrocarbonylation (CHC) is described. The CHC reactions are catalyzed by Rh-BIPHEPHOS complex under mild conditions. These CHC reaction processes involve (i) an extremely linear-selective hydroformylation of the terminal alkene moiety of a dehydrodipeptide substrate, (ii) intramolecular condensation to form cyclic N-acyliminium key intermediate, and (iii) the second cyclization through intramolecular nucleophilic addition of a heteoatom nucleophile to the cyclic N-acyliminium moiety to afford the corresponding 1-azabicyclo[x.y.0] system. This consecutive double cyclization process proceeds with extremely high diastereoselectivity in most cases. This method has been successfully applied to the syntheses of 1-azabicyclo[4.4.0], -[5.4.0], and -[4.3.0] systems. The mechanisms of the reactions and the rationale for the observed extremely high diastereoselectivity are presented. This Rh-catalyzed CHC process would serve as a highly efficient and versatile method for the syntheses of a variety of conformationally restrained dipeptides, peptidomimetics, alkaloids, and other biologically active natural or unnatural products.     

Selective sulfoxidation of thioethers and thioaryl boranes with nitrate, promoted by a molybdenum-copper catalytic system

The catalytic reduction of nitrate by molybdo-enzymes plays a central role in the global biological cycle of nitrogen. However, the use of nitrates as oxidants in synthetic organic chemistry is very limited and typically requires very strong acidic and other extreme reaction conditions. We have developed a highly chemoselective and efficient catalytic process for the sulfoxidation of thioethers and arylthioethers containing boronic acid or boronic ester functional groups, using nitrate salts as oxidants. This homogeneous catalytic reaction was carried out in acetonitrile, where the MoO(2)Cl(2)(OPPh(3))(2) complex 1 or a mixture of complex 1 with Cu(NO(3))(2) were used as catalysts. We examined the reaction mechanism using (1)H, (15)N, and (31)P NMR techniques and (18)O-labeled sodium nitrate (NaN(18)O(3)) and show that the thioethers are oxidized by nitrate, generating nitrite. Our work adds to the existing chemical transformations available for organoboron compounds, providing straightforward accessibility to a variety of new substrates that could be suitable for Suzuki cross-coupling chemistry.     

磺化碳催化Biginelli反应一锅法合成3,4-二氢-2(1H)-酮和硫酮(英文)

A sulfonated carbon material was shown to be a highly efficient,eco-friendly,and recyclable solid acid catalyst for the Biginelli reaction of β-ketoester,aldehyde,and urea or thiourea under solvent-free conditions.It gave 3,4-dihydropyrimidin-2(1H)-ones and-thiones in good to excellent yields.This method has the advantages of a simple procedure with easy work-up,short reaction time,and high yields.The catalyst can be recycled after a simple work-up and was reused four times without substantial reduction in activity.     

Benzylation of nitroalkanes using copper-catalyzed thermal redox catalysis: toward the facile C-alkylation of nitroalkanes

The C-alkylation of nitroalkanes under mild conditions has been a significant challenge in organic synthesis for more than a century. Herein we report a simple Cu(I) catalyst, generated in situ, that is highly effective for C-benzylation of nitroalkanes using abundant benzyl bromides and related heteroaromatic compounds. This process, which we believe proceeds via a thermal redox mechanism, allows access to a variety of complex nitroalkanes under mild reaction conditions and represents the first step toward the development of a general catalytic system for the alkylation of nitroalkanes.     

Rational Design of a ZnII MOF with Multiple Functional Sites for Highly Efficient Fixation of CO2 under Mild Conditions: Combined Experimental and Theoretical Investigation

The development of efficient heterogeneous catalysts suitable for carbon capture and utilization (CCU) under mild conditions is a promising step towards mitigating the growing concentration of CO₂ in the atmosphere. Herein, we report the construction of a hydrogen-bonded 3D framework, {[Zn(hfipbba)(MA)]⋅3 DMF}_n (hfipbba=4,4′-(hexaflouroisopropylene)bis(benzoic acid)) (HbMOF 1 ) utilizing Zn^II center, a partially fluorinated, long-chain dicarboxylate ligand (hfipbba), and an amine-rich melamine (MA) co-ligand. Interestingly, the framework possesses two types of 1D channels decorated with CO₂-philic (−NH₂ and −CF₃) groups that promote the highly selective CO₂ adsorption by the framework, which was supported by computational simulations. Further, the synergistic involvement of both Lewis acidic and basic sites exposed in the confined 1D channels along with high thermal and chemical stability rendered HbMOF 1 a good heterogeneous catalyst for the highly efficient fixation of CO₂ in a reaction with terminal/internal epoxides at mild conditions (RT and 1 bar CO₂). Moreover, in-depth theoretical studies were carried out using periodic DFT to obtain the relative energies for each stage involved in the catalytic reaction and an insight mechanistic details of the reaction is presented. Overall, this work represents a rare demonstration of rational design of a porous Zn^II MOF incorporating multiple functional sites suitable for highly efficient fixation of CO₂ with terminal/internal epoxides at mild conditions supported by comprehensive theoretical studies.     

Design, synthesis and antiviral potential of 14-aryl/heteroaryl-14H-dibenzo[a,j]xanthenes using an efficient polymer-supported catalyst

Polyethyleneglycol bound sulfonic acid (PEG-OSO?H), a chlorosulphonic acid-modified polyethylene glycol was successfully used as an efficient and eco-friendly polymeric catalyst in the synthesis of 14-aryl/heteroaryl-14H-dibenzo[a,j]xanthenes obtained from the reaction of 2-naphthol and carbonyl compounds under solvent-free conditions with short reaction times and excellent yields. The biological properties of these synthesized title compounds revealed that compounds 3b, 3c, 3f and 3i showed highly significant anti-viral activity against tobacco mosaic virus.     

Electrochemical,chemical and spectrophotometric investigation of the copper(II)-bicinchoninic acid reagent used for protein measurements

The use of a reagent containing copper (II), bicinchoninic acid (BCA) and tartrate buffered at pH 11.25 was studied voltammetrically, coulometrically, spectrophotometrically and chemically. The reagent exhibits three cathodic waves at rotating platinum disk and rotating glassy carbon electrodes. The two more-positive cathodic waves correspond to electrochemical reduction to copper (I)-bisbicinchoninate, Cu(BCA)₂^3?. The third cathodic wave is caused by reduction to metallic copper. A reaction mechanism is proposed that shows the major chemical species in the solution and the electrochemical reaction products. Voltammetric and chemical studies indicate that the reagent should be used with care for protein assays because it is subject to multiple chemical interferences.     

铜催化异噁唑还原环清洁高效合成1-氨基-2-乙酰基蒽醌简

以水为反应介质,水合肼为还原剂,研究了痕量铜催化3-甲基蒽醌-[1,2-c]-异噁唑还原开环反应以清洁高效合成1-氨基-2-乙酰基蒽醌,考察了不同种类过渡金属硝酸盐的催化性能,发现Cu（NO₃）₂性能最好. 加入 2.6% 的催化剂和1.3倍的水合肼,在室温反应 2 h,底物转化率和目标产物选择性分别可达到 97.2%和 95%,TON达到38. 产品结构经氢核磁谱和质谱得以确证,主要副产为羟基取代的1-氨基-2-乙酰基蒽醌. 此外,提出了铜催化 3-甲基蒽醌-[1,2-c]-异噁唑还原开环反应合成 1-氨基-2-乙酰基蒽醌的可能反应机理.     

SET‐LRP of acrylates in air

Single Electron Transfer‐Living Radical Polymerization (SET‐LRP) represents a robust and versatile method for the rapid synthesis of macromolecules with well defined topology. In SET‐LRP, certain combinations of solvents and ligands facilitate the disproportionation of in situ generated Cu(I) species into “nascent” Cu(0) and Cu(II) species. A combination of heterogeneous and “nascent” Cu(0) activation yields polymers with very high chain end functionality. Under suitable conditions the tolerance toward oxygen must be increased since Cu(0), the activator in SET‐LRP, acts as an oxygen scavenger in all inert gas purification systems. Here we demonstrate that SET‐LRP of methyl acrylate can be conducted in the presence of air. The addition of a small amount of reducing agent hydrazine hydrate to the reaction mixture reduces Cu₂O generated by the oxidation of Cu(0) with air, regenerating Cu(0) and allowing for the synthesis of polymers with predictable molecular weight and perfect retention of chain end functionality. The kinetics plots obtained under these conditions were identical to these generated by degassed samples. High conversions were achieved within a very short reaction time. In these SET‐LRP experiments, the reagents were not deoxygenated or subjected to standard degassing procedures such as freeze‐pump‐thaw or nitrogen sparging. This simple SET‐LRP procedure provides an efficient and economical approach to the synthesis of functional macromolecules. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1190–1196, 2010     

Highly selective colorimetric naked-eye Cu(II) detection using an azobenzene chemosensor

Colorimetric azobenzene based chemosensors 1 and 2 were designed for detection of transition-metal ions such as Cu(II) under physiological pH conditions. The internal charge transfer (ICT) sensors are highly colored, absorbing in the green. For 1, the Cu(II) recognition gives rise to red-to-yellow color changes that are visible to the naked-eye and reversible upon addition of EDTA, whereas for 2, which lacks the aromatic o-methoxy chelating group, no such changes were observed.     

A conducting coordination polymer based on assembled Cu9 cages

We report on a novel highly semiconducting 1D coordination polymer architecture obtained by the reaction of a Cu(II) salt with 2,2'-dipyridyldisulfide under microwave solvothermal conditions. This reaction proceeds with an unusual C-S and S-S bond cleavage of the 2,2'-dipyridyldisulfide ligand. The unprecedented architecture of this coordination polymer consists of a 1D chain formed by the assembling of Cu9 cluster cages. The electrical conductivity behavior of this novel material suggests new perspectives for the use of coordination polymers as electrical conducting materials.