Copper‐Mediated Formation of Aryl,Heteroaryl, Vinyl and Alkynyl Difluoromethylphosphonates: A General Approach to Fluorinated Phosphate Mimics

A general and efficient access to aryl, heteroaryl, vinyl and alkynyl difluoromethylphosphonates is described. The developed methodology using TMSCF₂PO(OEt)₂, iodonium salts and a copper salt provided a straightforward manifold to reach these highly relevant products. The reaction proved to be highly functional group tolerant and proceeded under mild conditions, giving the corresponding products in good to excellent yields. This method represents the first general synthetic route to this important class of fluorinated scaffolds, which are well‐recognized as in vivo stable phosphate surrogates.     

Cobaloxime(II)-initiated coupling of α,α,α-trihalomethylbenzenes

Bis(dimethylglyoximato) complexes of cobalt(II), cobaloxime(II), under mild conditions initiate coupling of α,α,α-trihalomethylbenzenes to form PhCX₂CX₂Ph (X  Cl), PhCXCXPh (X  Cl, Br) and mixtures of halocobaloxime products. Stoichiometry, product distribution, and control experiments suggest that coupling may result from the decomposition of a highly unstable haloalkylcobaloxime intermediate, Co(dmgH)₂(PhCX₂)(S(CH₃)₂). A general mechanism for the formation of this intermediate and its decomposition to the observed products is presented.     

Synthesis,structure and catalytic properties of Pdii-based bimetallic complexes with ferrocenecarboxylic acid

Novel highly soluble palladium-based complexes with ferrocenecarboxylic acid of general formula [Pd(lut)₂(FcCOO)₂] (lut is 2,6-or 3,4-lutidines) were synthesized and structurally characterized by single-crystal X-ray diffraction. The catalytic oxidation of 1,2-diphenyl-acetylene with these complexes gave dibenzo[a,e]pentalene derivative along with other products.     

Metal Ions in Biological Systems,Volume 3, High Molecular Complexes : ed. by Helmut Sigel,Dekker, New York, 1974, xiii + 289 pages, $ 22.75.

Complexes of the general type (RBPz₃)Rh(Alkene)₂ have been shown to involve a fluxional h₂-polypyrazolylborate ligand. The alkene groups are readily displaced by phosphines, N₂ or CO but only the latter yields stable products.     

Recent advances on the synthesis of flavans,isoflavans, and neoflavans

Heterocyclic compounds are the omnipresent structural cores comprising many natural and pharmaceutical products of biological significance. Significantly, heterocyclic compounds are widely distributed in nature, and also have applications in agrochemicals, sanitizers, as dyestuff, as copolymers, etc. Among heterocyles, flavonoids are a class of compounds that are highly interesting and constitute many natural products. In general, all flavanoids contains a basic core of C₆-C₃-C₆ of phenyl-benzopyran backbone. The relative placement of the phenyl group on to the benzopyran core makes further classification into flavanoids, isoflavanoids and neoflavanoids. Flavans (2-aryl chroman) are subclass of anthoxanthanes exhibits a broad spectrum of biological properties such as anti-inflammatory, anti-oxidant, and anti-malarial properties. Some representative naturally occurring products possessing flavan core are apigenin, luteolin, tangeretin, scutellarein, etc. On the other hand, some of the notable isoflavan-based natural products are glabridin and (S)-(−)-equol. Glabridin is isolated from Licorice roots, which regulates paraoxonase (PON₂) levels. While the simple isoflavan (S)-(−)-equol, is produced from soy isoflavone intake. Also, natural products such as dalbergichromene, centchroman, and (+)-myristinin A possess neoflavan (4-aryl-3,4-dihydro-2H-chromenes) core structure. Owing to their broad biological and pharmacological properties, synthetic chemists are fascinated in developing new routes toward their synthesis. As a result, a decent number of reports have been established in the literature. Thus, for the past 5 years of time frame, many new methodologies have been witnessed, for the synthesis of various flavan systems. This review emphasizes most of the significant methods on accomplishing flavans, isoflavans and neoflavans and also focused on their applications to the synthesis of relevant natural as well as biologically active products.     

Fe3O4@S‐ABENZ@VO: Magnetically separable nanocatalyst for the efficient,selective and mild oxidation of sulfides and oxidative coupling of thiols

Oxovanadium(IV) immobilized on Fe₃O₄@S‐ABEN is reported as a highly efficient nanocatalyst for the oxidation of sulfides and oxidative coupling of thiols (using H₂O₂ as green oxidant), the products of which are obtained in high to excellent yields. The products can be separated by a simple extraction with organic solvent and the catalyst is highly efficient, especially in terms of selectivity of desired product. The catalytic system can be recycled and reused without significant loss of catalytic activity.     

邻基效应促进的2-芳基硫代芳胺衍生物的简易合成

2-芳基硫代芳胺的结构广泛存在于许多具有重要生理、药理活性的天然产物、药物以及材料当中, 研究此类结构的构建对这些化合物的合成路线设计可以提供新的思路. 传统合成2-芳基硫代芳胺, 常需多步骤或高温、强碱条件下进行, 能进行此类反应的反应物有限, 所得产物收率不高. 选用三氟乙酰基作为芳胺氮原子上的保护基, 利用三氟乙酰基的邻位促进效应, 并采用碘化亚铜/L-脯氨酸的催化体系, 在乙二醇二甲醚中, 碳酸钾为碱, 于60 ℃一步实现N-三氟乙酰基邻碘代苯胺与芳基硫酚的偶联, 以高产率获得了N-三氟乙酰基-2-芳基硫代芳胺. 反应条件温和, 催化体系价廉易得, 反应操作简便.     

Diastereoselective Additive Trifluoromethylation/Halogenation of Isoxazole Triflones: Synthesis of All-Carbon-Functionalized Trifluoromethyl Isoxazoline Triflones

Highly functionalized 5-trifluoromethyl-2-isoxazoline derivatives featuring a triflyl (SO₂CF₃) group at the 4-position were successfully synthesized via diastereoselective trifluoromethylation and halogenation of isoxazole triflones using the Ruppert– Prakash reagent. The trifluoromethylation is quite general in terms of the substrates including 3,5-diaryl isoxazole triflones and 3-aryl-5-styrylisoxazole triflones to provide products in high yields with excellent diastereoselectivities. The highly functionalized 5-trifluoromethyl-2-isoxazoline derivatives are expected to be a new class of antiparasiticides. Thus the triflyl group both activates isoxazoles and the 4-postion of CF₃ adducts, and has a potential biological function.     

Preparation,characterization and catalytic activity of a nano-Co(II)-catalyst as a high efficient heterogeneous catalyst for the selective oxidation of ethylbenzene,cyclohexene, and benzyl alcohol

This paper reports the preparation of a nano-Co(II)-catalyst (NCC) by anchoring of Co ions on immobilized bipyridylketone over the nano-sized SiO₂/Al₂O₃ mixed oxides. The nano-Co(II)-catalyst has been characterized by elemental analysis, BET, FT-IR, DR UV–vis and SEM. The catalytic activity of the catalyst towards the oxidation of ethylbenzene, cyclohexene, and benzylalcohol to different chemically and pharmaceutically important products were evaluated with tert-butyl hydroperoxide (TBHP) in the absence of solvent. Under optimized conditions, the nano-catalyst proved highly selective towards the acetophenone, 2-cyclohexene-1-one and benzaldehyde as reaction products, with excellent conversion rates.     

Catalytic syntheses of alternating, stereoregular ethylene/cycloolefin copolymers

The alternating stereospecific copolymerization of ethylene with cycloolefins (cyclopentene, cycloheptene, and cyclooctene) has been investigated with a series of constrained geometry titanium catalysts (CGCs). The metallocene IndSiMe₂(^tBuN)TiCl₂ was found to generate highly alternating and stereoregular cycloolefin-co-ethylene polymers while Me₄CpSiMe₂(^tBuN)TiCl₂ produced alternating atactic polymers. In addition, novel Ti-complexes of the general formula benz[6.7]indenylSiMe₂(^tBuN)TiMe₂ were synthesized and fully characterized. The chiral indenyl Ti complexes were found to produce exclusive 1,2-enchainment of the cycloolefin to generate highly stereoregular and alternating copolymers.     

Chemo-, Stereo- and Regioselective Fluoroallylation/Annulation of Hydrazones with gem-Difluorocyclopropanes via Tunable Palladium/NHC Catalysis

Defluorinative manipulation of polyfluorinated molecules has shown great promise due to its granting of synthetic versatility to inert C−F bonds. The development of chemo-, stereo- and regioselective strategies to realize highly efficient formation of either the linear/branched or E/Z products from gem-difluorocyclopropanes (gem-F₂CPs) is a challenging task. Herein, we have realized palladium/NHC-catalyzed fluoroallylation/annulation of hydrazones with gem-F₂CPs that incorporate the hydrazone N₂ moiety into the products. The thermodynamically unstable fluorinated E-allylation products with aryl ketone hydrazones were obtained for the first time, while the di-alkyl ketone hydrazones yielded the monofluorinated products with branched selectivity under similar reaction conditions. With aldehyde hydrazones, two kinds of pyrazoles were obtained via a defluorinative allylation/annulation cascade, in which different carbon atoms of gem-F₂CPs could be incorporated into the pyrazole rings regiospecifically. DFT calculations revealed that the divergent selectivity was kinetically controlled and the final C−C bond formation proceeded through a 7-membered TS.     

Selective CO2 Electroreduction to Ethylene and Multicarbon Alcohols via Electrolyte‐Driven Nanostructuring

Production of multicarbon products (C₂₊) from CO₂ electroreduction reaction (CO₂RR) is highly desirable for storing renewable energy and reducing carbon emission. The electrochemical synthesis of CO₂RR catalysts that are highly selective for C₂₊ products via electrolyte‐driven nanostructuring is presented. Nanostructured Cu catalysts synthesized in the presence of specific anions selectively convert CO₂ into ethylene and multicarbon alcohols in aqueous 0.1 m KHCO₃ solution, with the iodine‐modified catalyst displaying the highest Faradaic efficiency of 80 % and a partial geometric current density of ca. 31.2 mA cm^?2 for C₂₊ products at ?0.9 V vs. RHE. Operando X‐ray absorption spectroscopy and quasi in situ X‐ray photoelectron spectroscopy measurements revealed that the high C₂₊ selectivity of these nanostructured Cu catalysts can be attributed to the highly roughened surface morphology induced by the synthesis, presence of subsurface oxygen and Cu⁺ species, and the adsorbed halides.     

Synthesis,X‐ray structure,characterization and catalytic activity of a polymeric manganese(II) complex with iminodiacetate

A polymeric manganese(II) complex with the general formula [Mn(O₂CCH₂NH₂CH₂CO₂)₂(H₂O)₂]_n from reaction of iminodiacetatic acid and manganese(II) perchlorate under nitrogen in water, was synthesized and characterized. The structure of the complex was determined using single‐crystal X‐ray diffraction, elemental analysis, IR and UV‐vis spectra. This complex exhibited excellent catalytic activity and selectivity for oxidation of various alcohols and sulfides to the corresponding aldehydes/ketone and sulfoxides using urea hydrogen peroxide and oxone (2KHSO₅·KHSO₄·K₂SO₄), respectively, as oxidants under air at room temperature. The easy preparation, mild reaction conditions, high yields of the products, short reaction time, no over‐oxidation products, high selectivity and inexpensive system make this catalytic system a useful method for oxidizing various alcohols and sulfides. Copyright © 2011 John Wiley & Sons, Ltd.     

A general gas‐assisted three‐liquid‐phase extraction method for separation and concentration of puerarin, 3′‐methoxydaidzin,puerarinxyloside, daidzin and daidzein from puerariae extract

In this work, a general and novel separation technique gas‐assisted three‐liquid‐phase extraction was established and applied in separating and concentrating isoflavonoids from the actual sample of puerariae extract by one step. For the gas‐assisted three‐liquid‐phase extraction method, optimal conditions were selected: polyethylene glycol 2000 and ethyl acetate as the flotation solvent, pH 5, (NH₄)₂SO₄ concentration 350 g/L in aqueous phase, N₂ flow rate 30 mL/min, flotation time 50 min, and flotation twice. Five isoflavonoids compounds puerarin, 3′‐methoxydaidzin, puerarinxyloside, daidzin and daidzein were separated with recoveries of 82, 84, 80, 88 and 89%, respectively. The separated products were purified by preparative high‐performance liquid chromatography, and the purity of the final products was >96%. The established general gas‐assisted three‐liquid‐phase extraction was used to separate anthraquinones from Cassiae Semen under the optimal conditions, and the recoveries were >75%. The experimental results showed that the established gas‐assisted three‐liquid‐phase extraction method is a general technique for separating active compounds from herb extract.     

The reaction of fluoroxysulfate,sof-. liith aromatic compounds: catalysis by acids

The effects of the acid catalysts HF, H₂S0₄, BF₃, CF₃S0₃H, FSO₃H, and SbF₅.FS0₃H on the reactions of CsSO₄F with toluene, nitrobenzene and naphthalene in CH₃CN have been studied. The catalys general accelerate reaction and enhance yields of ring-fluorinated products. Efficacity roughly parallels H₀ of the acids, though H₂S0₄ is more effective than stronger acids for the fluorination of naphthalene. Combined room temperature yields of fluorine-substituted products are as much as 45-50% for toluene and naphthalene and up to 30% for nitrobenzene. The predominant products are o-fluorotoluene, 1- fluoronaphthalene, and m-fluoronitrobenzene. With naphthalene the isomer selectivity is considerably less than in the absence of catalyst. Low yields (10%) of monomeric oxygenated products are obtained, along with considerable oxygen- and fluorine-containing dimers and higher polymers. The results are interpreted in terms of acid-catalyzed electrophilic fluorination or oxygenation, followed by further fluorination and/or free-radical-induced oxidative coupling of the oxygenated products.     

Aqueous electrochemistry of binuclear copper complex with Robson-type ligand: dissolved versus surface-immobilized reactant

The electrochemical behaviour of binuclear copper complex with Robson-type ligand [Cu₂L]Cl₂ in aqueous medium is studied by cyclic voltammetry at highly oriented pyrolytic graphite, glassy carbon and gold electrodes. The overall reduction from solution of this reactant is found to be irreversible resulting in metallic copper formation. It is also complicated by chemical transformations of Cu(I) containing species. When attached to carbon support, [Cu₂L]Cl₂ is redox active in aqueous medium in the same potential range. The reduction is more reversible if reactant is immobilized at HOPG surface, and is in general agreement with reversible copper demetallation scheme. For dissolved reactant, the contribution of surface-attached species is screened by predominating voltammetric response of irreversible reduction. These conclusions are supported by data on the reduction of free protonated ligand and its hydrolysis products. Ex situ STM is applied to characterize electrode surfaces modified by [Cu₂L]Cl₂. Adsorbate monolayer of periodic structure is observed at highly oriented pyrolytic graphite (HOPG). Adsorption is more disordered at GC and less strong at polycrystalline gold support.     

Synthesis of highly sterically hindered niobium and tantalum alkoxides and their microhydrolysis in strongly basic medium

We have investigated the interaction of niobium and tantalum alkoxides with pinacol and are reporting here isolation and structural characterization of the products, attractive potential precursors of materials with hierarchical porosity. The general feature in the reactivity of alkoxide complexes with additional ligands is that stabilization of the complexes is achieved due to Brønsted acidity of the ligand and possibility of formation of hydrogen bonds in the structure. Presence of strong organic bases does not influence the complex formation. We were able to isolate, for example, highly moisture-sensitive ortho-pinacolates of Nb and Ta, M(O₂C₆H₁₂)₂(OC₆H₁₂OH), in the presence of excess of triethylamine. The earlier attempts to prepare these complexes were unsuccessful because of extremely high solubility and easy hydrolysis of these species. The first step in microhydrolysis of M(O₂C₆H₁₂)₂(OC₆H₁₂OH), M = Nb, Ta, independently of basicity of the medium provides M₂O(O₂C₆H₁₂)₂(OC₆H₁₂OH)₄, even those highly moisture-sensitive in solution. The general conclusion of this work is that the Lewis acidity and blocking of the coordination sites by bulky alkoxide ligands does not play any important role. The reactivity of the species is not in any way hindered by the complete blocking of the metal centers.     

Palladium catalyzed three component coupling reaction between chromones, alcohols, and allylic acetates: diversity-oriented synthesis of highly substituted chromones

This paper describes the palladium catalyzed highly efficient three component coupling (TCC) reactions between chromones, allylic acetates, and alcohols, which lead to a library of multiply substituted chromones. The activity of various palladium catalysts, such as Pd(PPh₃)₄ and Pd₂dba₃·CHCl₃ and their combination with various bisphosphine ligands, was investigated by using THF as a solvent, which revealed that Pd(PPh₃)₄ catalyst was the best one. The reaction most probably proceeds via the formation of benzopyrilium cation, generated from the reaction between chromones and allyl acetate, in the presence of palladium catalyst. The subsequent trapping of the benzopyrilium cation by alcohols would give the corresponding products in excellent yields. This alkoxy-allylation reaction was highly diastereoselective and only one diastereomer was obtained in all the cases.     

Dendritic analogues of engineering plastics - a general one-step synthesis of dendritic polyaryl ethers

The first general single-step route to dendritic or cascade polyaryl ethers analogous to common linear polyaryl ethers is described. The sodium salts of four AB₂ monomers each containing a single phenolic hydroxyl group and two aryl fluorides activated toward nucleophilic substitution by carbonyl, sulphonyl, or tetrafluorophenyl moieties are shown to polymerize in hot N, N-dimethylacetamide. The products are high molecular weight polymers (7000 < M_n < 36000), have narrow polydispersities (1.50 < M_w/M_n < 4.50), and are highly soluble in organic solvents. The molecular weights of two of the polymers increase with monomer concentration. The polymers are thermally stable (500 °C under N₂) and have glass transition temperatures ranging from 135 to 231 °C.     

Organosilicon compounds in supercritical carbon dioxide: Synthesis,polymerization, modification,and production of new materials

The main promising opportunities for the advantageous combination of organosilicon compounds and supercritical carbon dioxide both as a solvent and as a reagent in chemical processes are analyzed. The main processes of polymerization and modification of polymer matrices that are performed in supercritical СО₂ with the use of organosilicon materials of various types are outlined. Methods for the obtaining organosilicon polymers and polymer-inorganic composites and methods for the application of siloxane stabilizers in the dispersion polymerization of monomers in supercritical СО₂ are described. Studies of the insertion of a СО₂ molecule into Si–H, Si–N, and Si–O–Me bonds in reactions that feature exceptionally high chemical selectivity and afford a wide spectrum of products potentially useful for application in the chemistry of polymer materials are considered. It is shown that the silylation of surfaces of various types and morphologies in the medium of supercritical СО₂ is a rapidly developing green approach that makes it possible to obtain highly uniform defect-free coatings with variable desired functionality.