Cobalt-catalyzed reductive coupling of activated alkenes with alkynes

Cobalt complex/Zn systems effectively catalyze the reductive coupling of activated alkenes with alkynes in the presence of water to give substituted alkenes with very high regio- and stereoselectivity in excellent yields. While the intermolecular reaction of acrylates, acrylonitriles, and vinyl sulfones with alkynes takes place in the presence of CoI2(PPh3)2/Zn, the reaction of enones and enals with alkynes requires the use of the CoI2(dppe)/Zn/ZnI2 system. The intramolecular reductive coupling of activated alkenes (enones, enals, acrylates, and acrylonitriles) with alkynes also works efficiently. Further a variety of cyclic lactones and lactams were prepared using this methodology. Possible mechanistic pathways are proposed based on a deuterium-labeling experiment carried out in the presence of D2O.     

Pinacol coupling reaction of beta-halo-alpha,beta-unsaturated aldehydes promoted by TiI4

The pinacol reaction of beta-halogenated alpha,beta-unsaturated aldehydes was promoted by titanium tetraiodide to give coupling products in good yields with high dl-selectivity. Subsequent reduction with H(2)/Pd-C gave saturated vic-diols in good yields. Heck coupling reaction enabled the displacement of halogens with vinyl groups without the loss of stereochemical integrities. [reaction: see text]     

Nickel-catalyzed coupling of isocyanates with 1,3-iodoesters and halobenzenes: a novel method for the synthesis of imide and amide derivatives

Substituted imide and amide derivatives were conveniently prepared from the reaction of isocyanates with o-iodobenzoates and haloarenes catalyzed by the NiBr2(dppe)/dppe/Zn system in moderate to good yields with excellent tolerance of functional groups.     

Palladium-catalyzed tetrakis(dimethylamino)ethylene-promoted reductive coupling of aryl halides

Tetrakis(dimethylamino)ethylene (TDAE)/cat. PdCl(2)(PhCN)(2)-promoted reductive coupling of aryl bromides having either electron-donating or electron-withdrawing groups on their para- and/or meta-position proceeded smoothly to afford the corresponding biaryls in good to excellent yields. Notably, TDAE is such a mild reductant that easily reducible groups, such as carbonyl and nitro groups, are tolerate. A similar reductive coupling of ortho-substituted aryl bromides did not occur at all. The proper choice of palladium catalysts is essential for the reductive coupling; thus, PdCl(2)(PhCN)(2), PdCl(2)(MeCN)(2), Pd(hfacac)(2), Pd(2)(dba)(3), PdCl(2), and Pd(OAc)(2) were used successively for this reaction, but phosphine-ligated palladium catalysts such as Pd(PPh(3))(4), PdCl(2)(PPh(3))(2), and Pd(dppp) did not promote the reaction. The reductive coupling did not occur with nickel catalysts such as NiBr(2), NiCl(2)(bpy), and Ni(acac)(2). The TDAE/cat. palladium-promoted reductive coupling of aryl halides having electron-withdrawing groups took place more efficiently than that of aryl halides substituted with electron-donating groups. A plausible mechanism of TDAE/cat. palladium-promoted reaction is discussed.     

Synthesis of meso-azulenylporphyrins

[reaction: see text] meso-Azulenylporphyrins 1-4 were prepared by Suzuki-Miyaura coupling or the Ziegler-Hafner method. 1-Azulenyl and 6-azulenyl groups are indeed acting as electron-donating and electron-accepting substituents toward Zn(II) porphyrin. Fluorescence of Zn(II) porphyrin in the dyads is strongly quenched depending upon substitution position of azulene in order of 2 > 1 > 4 > 3.     

o-Dihaloarenes as aryne precursors for nickel-catalyzed [2 + 2 + 2] cycloaddition with alkynes and nitriles

o-Dihaloarenes acting as aryne precursors react with acetylenes and nitriles catalyzed by the NiBr(2)(dppe)/dppe/Zn system to give substituted naphthalene, phenanthridine or triphenylene derivatives depending on the reaction conditions in moderate to excellent yields with good tolerance of functional groups.     

Synthesis of trans-Disubstituted Alkenes by Cobalt-Catalyzed Reductive Coupling of Terminal Alkynes with Activated Alkenes

A cobalt-catalyzed reductive coupling of terminal alkynes, RC?CH, with activated alkenes, R'CH?CH(2) , in the presence of zinc and water to give functionalized trans-disubstituted alkenes, RCH?CHCH(2) CH(2) R', is described. A variety of aromatic terminal alkynes underwent reductive coupling with activated alkenes including enones, acrylates, acrylonitrile, and vinyl sulfones in the presence of a CoCl(2) /P(OMe)(3) /Zn catalyst system to afford 1,2-trans-disubstituted alkenes with high regio- and stereoselectivity. Similarly, aliphatic terminal alkynes also efficiently participated in the coupling reaction with acrylates, enones, and vinyl sulfone, in the presence of the CoCl(2) /P(OPh)(3) /Zn system providing a mixture of 1,2-trans- and 1,1-disubstituted functionalized terminal alkene products in high yields. The scope of the reaction was also extended by the coupling of 1,3-enynes and acetylene gas with alkenes. Furthermore, a phosphine-free cobalt-catalyzed reductive coupling of terminal alkynes with enones, affording 1,2-trans-disubstituted alkenes as the major products in a high regioisomeric ratio, is demonstrated. In the reactions, less expensive and air-stable cobalt complexes, a mild reducing agent (Zn) and a simple hydrogen source (water) were used. A possible reaction mechanism involving a cobaltacyclopentene as the key intermediate is proposed.     

Cocyclotrimerization of 6-alkynylpurines with alpha,omega-diynes as a novel approach to biologically active 6-arylpurines

Transition metal complex catalyzed cocyclotrimerization of 6-alkynylpurines 1 with various diynes enables the preparation of a plethora of substituted 6-arylpurines 3 in good yields. The most general catalyst for the reaction is a user-friendly system based on a nickel-phosphine complex and reductant (NiBr(2)(dppe)/Zn) in MeCN. The reaction conditions are compatible with various protective groups on the purine moiety (Bn, THP). As far as other potential catalysts were concerned, only CoBr(PPh(3))(3) showed reasonable activity in cocyclotrimerization of alkynylpurines with dipropargyl ether. A comparison of catalytic with stoichiometric approaches and the ligand effect in the catalyst is also given. Cytostatic activity screening of title 6-arylpurines was performed and several moderately active compounds were found.     

Efficient route to atropisomeric ligands--application to the synthesis of MeOBIPHEP analogues

A highly efficient Pd-catalyzed P-C coupling reaction of easily accessible atropisomeric bisphosphane is described in the presence of various electron-poor aromatic iodides. The reactions are conducted in the presence of a Pd(II)/dppf catalyst in acetonitrile at 80 °C. The reaction conditions are compatible with several electron-withdrawing groups such as esters, cyano, chloro, and trifluoromethyl groups and lead to atropisomeric MeOBIPHEP derivatives in good to excellent yields and high enantiomeric purities.     

Direct coupling of benzene with olefin catalyzed by Pd(OAc)(2) combined with heteropolyoxometalate under dioxygen

The oxidative coupling reaction of benzenes with alkenes was successfully achieved by the Pd(OAc)(2)/molybdovanadophosphoric acid (HPMoV)/O(2) system. For example, the reaction of benzene with ethyl acrylate by the above catalytic system in acetic acid afforded ethyl cinnamate as a major product in satisfactory yield.     

Ruthenium-complex-catalyzed regio- and stereoselective linear codimerization of 2-norbornenes with acrylic compounds

A linear codimerization of 2-norbornenes with acrylic compounds such as acrylates and an acrylamide proceeded efficiently by ruthenium catalyst systems, RuCl3(tpy)/Zn (tpy = 2,2':6',2' '-terpyridine) or [RuCl2(C6H6)]2/Zn in a primary or secondary alcoholic solvent, to afford the corresponding exo-trans-2-norbornylacrylates as major products regio- and stereoselectively along with a small amount of cis isomers. The reaction of 2,5-norbornadiene with methyl acrylate also gave the linear exo-trans codimer, which was effectively catalyzed by the addition of triarylphosphines to the RuCl3(tpy)/Zn catalyst system.     

Rational syntheses of cyclic hexameric porphyrin arrays for studies of self-assembling light-harvesting systems.

Two new cyclic hexameric arrays of porphyrins have been prepared in a rational, convergent manner. The porphyrins in each cyclic hexamer are joined by diphenylethyne linkers affording a wheel-like array with a diameter of approximately 35 A. One array is comprised of five zinc (Zn) porphyrins and one free base (Fb) porphyrin (cyclo-Zn(5)FbU) while the other is comprised of an alternating sequence of two Zn porphyrins and one Fb porphyrin (cyclo-Zn(2)FbZn(2)FbU). The prior synthesis employed a one-flask template-directed process and afforded alternating Zn and Fb porphyrins or all Zn porphyrins. More diverse metalation patterns are attractive for manipulating the flow of excited-state energy in the arrays. The rational synthesis of each array employed three Pd-mediated coupling reactions with four tetraarylporphyrin building blocks bearing diethynyl, diiodo, bromo/iodo, or iodo/ethynyl groups. The final ring closure yielding the cyclic hexamer was achieved by reaction of a porphyrin pentamer + porphyrin monomer or the joining of two porphyrin trimers. In the presence of a tripyridyl template, the yields of the 5 + 1 and 3 + 3 reactions ranged from 10 to 13%. The 5 + 1 reaction in the absence of the template proceeded in 3.5% yield, thereby establishing the structure-directed contribution to cyclic hexamer formation. The 3 + 3 route relied on successive ethyne + iodo/bromo coupling reactions. One template-directed route to cyclo-Zn(2)FbZn(2)FbU employed a magnesium porphyrin, affording cyclo-Zn(2)FbZn(2)MgU from which magnesium was selectively removed. The arrays exhibit absorption spectra that are nearly the sum of the spectra of the component parts, indicating weak electronic coupling. Fluorescence spectroscopy showed that the quantum yield of energy transfer in toluene at room temperature from the Zn porphyrins to the Fb porphyrin(s) was 60% in cyclo-Zn(5)FbU and 90% in cyclo-Zn(2)FbZn(2)FbU. Two dipyridyl-substituted porphyrins, a Zn tetraarylporphyrin and a Fb oxaporphyrin, have been synthesized for use as guests in the cyclic hexamers, affording self-assembled arrays for light-harvesting studies.     

The influence of aminobenzoic acid on Zn(II) electroreduction on a mercury electrode in water-methanol

Summary The influence of the isomers of aminobenzoic acid on the reaction Zn(II)/Zn(Hg) was studied in water-methanol mixtures. Theo- andm-isomers accelerate this reaction in all investigated solutions. The standard rate constants are similar at the same degree of electrode coverage with these isomers in water and mixed solutions.p-Aminobenzoic acid inhibits the process of Zn(II)/Zn(Hg) electroreduction. The results suggest that the decisive role in the acceleration is played by the formation of the active complex inside the adsorption layer.

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Der Einfluß von Aminobenzoesäure auf die Elektroreduktion von Zn(II) an einer Quecksilberelektrode in Methanol-Wasser

Zusammenfassung Der Einfluß der verschiedenen Isomeren von Aminobenzoesäure auf die Reduktion von Zn(II) an einer Quecksilberelektrode wurde in Methanol-Wasser-Mischungen untersucht. Dieo- undm-Isomeren beschleunigen die Reaktion, und die Reaktionsgeschwindigkeiten sind in Wasser und in Methanol-Wasser gleich. Die Beschleunigung wird wahrscheinlich durch Bildung des aktivierten Komplexes innerhalb der Adsorptionsschicht verursacht.p-Aminobenzoesäure hemmt die Elektroreduktion.

     

A RuH(2)(CO)(PPh(3))(3)-catalyzed regioselective arylation of aromatic ketones with arylboronates via carbon-hydrogen bond cleavage

When the reaction of aromatic ketones with arylboronates (arylboronic acid esters) using RuH(2)(CO)(PPh(3))(3) (3) as a catalyst was conducted in toluene, the corresponding arylation product was obtained in moderate yields. In this case, a nearly equivalent amount of a benzyl alcohol derived from a reduction of an aromatic ketone was also formed. The use of aliphatic ketones, such as pinacolone and acetone, as an additive or a solvent dramatically suppressed the reduction of the aromatic ketones and, as a result, ortho-arylation products were obtained in high yield based on the aromatic ketones. In these reactions, the aliphatic ketone functioned as a scavenger of ortho-hydrogens of the aromatic ketones and the B(OR)(2) moiety of the arylboron compound (HB species). A variety of aromatic ketones, such as acetophenones, acetonaphthones, tetralones, and benzosuberone, could also be used in this coupling reaction. Several arylboronates containing electron-donating (NMe(2), OMe, and Me) and -withdrawing (CF(3) and F) groups were also applicable to this coupling reaction. Intermolecular competitive reaction using pivalophenone-d(0)() and -d(5) and intramolecular competitive reaction using pivalophenone-d(1) were carried out using 3 as a catalyst. The k(H)/k(D) value for the intermolecular competitive reaction was substantially different, compared with intramolecular competitive reaction. This strongly suggests the production of an intermediate where the ketone carbonyl is coordinated to the ruthenium involved in this catalytic reaction. (1)H and (11)B NMR studies using 2'-methylacetophenone, phenylboronate (2), and pinacolone (6) indicate that 6 functions effectively as a scavenger of the HB species.     

Zn-Al水滑石催化碳酸二甲酯与苯酚酯交换反应的研究

用共沉淀法制备了Zn-Al水滑石,并用于多相催化酯交换合成碳酸二苯酯的反应.研究了不同n(Zn)/n(Al)比的水滑石及其焙烧产物等对酯交换反应的催化活性.结果表明,Zn-Al水滑石催化剂对该反应的催化活性和选择性很高,当n(Zn)/n(Al)=3时,在150～180℃,n(PhOH)/n(DMC)=2,催化剂用量为反应物总质量的1.5%,在反应时间为12h的条件下,DMC的转化率达到55.9%,DPC和MPC的收率分别为25.3%和27.0%,酯交换产物的选择性达到93.6%.利用XRD,TG-DTA和TEM等手段对催化剂进行了表征.     

Pd(OAc)2-catalyzed oxidative coupling reaction of benzenes with olefins in the presence of molybdovanadophosphoric acid under atmospheric dioxygen and air

The direct oxidative coupling reaction of benzenes with alkenes bearing an electron-withdrawing group was successfully achieved by the use of Pd(OAc)(2)/molybdovanadophosphoric acid (HPMoV) as the key catalyst under O(2) or air atmosphere. Thus, the reaction of benzene with ethyl acrylate under air (1 atm) assisted by Pd(OAc)(2)/HPMoV afforded ethyl cinnamate as a major product in satisfactory yield (74%). This catalytic system could be extended to the coupling reactions between various substituted benzenes and alkenes through the direct aromatic C-H bond activation. In the reaction of benzene with ethyl acrylate under O(2) (1 atm), the best turn-over number (TON) of Pd(OAc)(2) reached was 121. This reaction provides a green route to cinnamate derivatives, which are important precursors of a variety of pharmaceuticals.     

聚苯乙烯基偶氮聚合物的合成研究

改进了聚苯乙烯的硝化、还原、重氮化和偶合反应路线 (NRDC) ,使每步反应都得到很高的产率 ,并利用大分子重氮盐 (MDS)分别与苯胺、N 烃基苯胺和酚等三类化合物偶合 ,得到相应的聚苯乙烯基偶氮聚合物 .核磁共振分析结果证明了产物的高偶联率 .通过对大分子重氮盐热稳定性的研究 ,发现偶合反应之后需要一步加热反应以消除残余重氮基团 .还研究了这些聚合物的紫外 可见吸收光谱性质 ,氨 (胺 )基偶氮产物的水溶液表现出了明显的pH敏感性     

CaSiO3∶Pb,Mn荧光粉的ZnO∶Al包覆研究

以Zn(NO3)2•6H2O和AlCl3•6H2O为原料, 借助CO(NH2)2的水解反应, 采用化学均相共沉淀方法和热处理工艺, 在自制CaSiO3∶Pb, Mn红色荧光粉表面包覆ZnO∶Al, 形成透明导电层. 运用数字万用表和自制测量盒对粉体的电阻率进行测量, 比较了包覆率n(Zn)/n(Ca)、n(Al)/n(Zn), 热处理温度和热处理时间对粉体电阻率的影响; 优化出包覆条件和热处理条件: n(Zn)/n(Ca)=10%, n(Al)/n(Zn)=5%, 75 ℃水解1.5 h, 500 ℃热处理45 min. 对包覆样品进行了室温光致荧光(PL)测量, X射线衍射(XRD)结构分析和透射电子显微镜(TEM)形貌观察. 结果显示, 当n(Zn)/n(Ca)=10%时, 在CaSiO3∶Pb, Mn荧光粉表面形成了连续的ZnO∶Al敷膜, 荧光粉的电阻率明显降低, 并且保持了良好的光致发光性质.     

共沉淀浸渍法制备由合成气直接合成二甲醚的Cu-Mn催化剂

采用共沉淀浸渍法,制备了直接合成二甲醚的Cu-Mn-Zn催化剂,通过对组成成分及其配比的研究,发现Cu含量一定的条件下,n(Zn)/n(Mn)摩尔比对催化剂性能有较大的影响,当n(Zn)/n(Mn)=1/3～1/2时,催化剂对CO的转化率和对二甲醚的选择性达到最佳,分别为53.6%和63.5%；如锰添加比例过大,对催化剂催化合成二甲醚有微弱抑制；添加锌比例过大,会大大降低CO的转化率。载体Y分子筛的含量对催化剂性能也有影响,用量过大将降低催化剂的活性和对二甲醚的选择性,当其含量为33%时,催化剂上CO转化率和选择性可分别达到66%和68%,且催化剂活性随分子筛含量减少不再有明显的变化。     

Mass discrimination during MC-ICPMS isotopic ratio measurements: Investigation by means of synthetic isotopic mixtures (IRMM-007 series) and application to the calibration of natural-like zinc materials (including IRMM-3702 and IRMM-651)

A long known way of anchoring isotope ratio values to the SI system is by means of gravimetrically prepared isotopic mixtures. Thermal ionization mass spectrometry (TIMS) is the traditionally associated measurement technique, but multi-collector double focusing inductively coupled plasma (MC-ICP)-MS now appears to be an attractive alternative. This absolute calibration strategy necessitates that mass discrimination effects remain invariant in time and across the range of isotope ratios measured. It is not the case with MC-ICPMS and the present work illustrates, in the case of Zn isotopic measurements carried out using locally produced synthetic Zn isotope mixtures (IRMM-007 series), how this calibration strategy must be adjusted. First, variation in mass discrimination effects across the measurement sequence is propagated as an uncertainty component. Second, linear proportionality during each individual measurement between normalized mass discrimination and the average mass of the isotope ratios is used to evaluate mass discrimination for the ratios involving low abundance isotopes. Third, linear proportionality between mass discrimination and the logarithm of the isotope ratio values for n(67Zn)/n(64Zn) and n(68Zn)/n(64Zn) in the mixtures is used iteratively to evaluate mass discrimination for the same ratios in the isotopically enriched materials. Fourth, ratios in natural-like materials (including IRMM-3702 and IRMM-651) are calibrated by external bracketing using the isotopic mixtures. The relative expanded uncertainty (k = 2) estimated for n(68Zn)/n(64Zn) and n(67Zn)/n(64Zn) ratio values in the synthetic isotopic mixtures and the natural-like zinc samples was in the range of 0.034 to 0.048%. The uncertainty on the weighing (0.01%, k = 1) was the largest contributor to these budgets. The agreement between these results and those obtained with a single detector TIMS and with another MC-ICPMS further validated this work. The absolute isotope ratio values found for IRMM-3702-material also proposed as "delta 0" for delta-scale isotopic measurements-are n(66Zn)/n(64Zn) = 0.56397 (30), n(67Zn)/n(64Zn) = 0.082166 (35), n(68Zn)/n(64Zn) = 0.37519 (16), and n(70Zn)/n(64Zn) = 0.012418 (23). The derived Zn atomic weight value Ar(Zn) = 65.37777 (22) differs significantly from the current IUPAC value by Chang et al. [1]. Remeasurement, with isotopic mixtures from the IRMM-007 series, of the Zn isotope ratios in the same Chang et al. [1] material have revealed large systematic differences (1.35 (27)% per atomic mass unit) that suggest unrecognized measurement biases in their results.