Kinetic separation methodology for the stereoselective synthesis of (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated esters via the palladium-catalyzed carboalkoxylation of 1-bromo-1-fluoroalkenes

[reaction: see text] Methodology for the stereoselective preparation of both (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated esters is described. 1-Bromo-1-fluoroalkenes (E/Z approximate 1:1) can be isomerized to high E/Z ratio mixtures, which participate in palladium-catalyzed carboalkoxylation and lead to (Z)-alpha-fluoro-alpha,beta-unsaturated esters in high stereoselectivity. The same starting material can also be kinetically reduced to get an E/Z ratio of 0:100; similar carboalkoxylation reaction at 70 degrees C affords (E)-alpha-fluoro-alpha,beta-unsaturated esters stereospecifically.     

梨小食心虫性信息素的新法合成

梨小食心虫 (Grapholia molesta)是一种世界性果树害虫 ,主要危害梨、桃和苹果等果树 . 1 96 5年Geroge等 [1] 从该雌蛾腹部分离得到其性信息素 . 1 96 9年 Roelofs等 [2 ] 鉴定其结构为 8(Z/E) -十二碳烯 - 1 -醇乙酸酯 (6 ) .国内外对其生物活性进行了大面积田间试验 ,并用于     

Electrocyclic reactions : Stereochemistry of the triene electrocyclization

Four trienes of known stereochemistry have been prepared and their thermal cyclization studied to ascertain the general stereochemistry of thermal triene electrocyclic reactions. A mixture containing (Z)-1,2-dicyclohexenylethylene was obtained by semihydrogenation. Spectra evidence for thermal cyclization of the triene was obtained, but inability to isolate pure materials canceled plans for stereochemical study.A stereoselective synthesis for (E,Z,E)-2,4,6-octatriene was devised and a pure sample was cyclized thermally to give a 5,6-dimethylcyclohexadiene. Oxidative cleavage of this diene gave meso-2,3-dimethylsuccinic acid. Pure samples of (Z,Z,E)- and (Z,Z,Z)-2,4,6-octatrienes were prepared and found to interconvert thermally at 110°. Cyclization of the equilibrium mixture occurred at 178° to give a 5,6-dimethylcyclohexadiene which gave rac-2,3-dimethylsuccinic acid upon oxidative cleavage. Evidence is presented to suggest that the (E,Z,Z) isomer is the actual reactant undergoing cyclization. Both cyclohexadienes were shown to undergo a 1,5-hydrogen shift to form 1,6-dimethyl-1,3-cyclohexadiene.Rates of the electrocyclic reactions were measured in pentane solution, and thermodynamic activation parameters were ascertained. The results are: (E,Z,E) k(132°) = 4·45 × 10^?5 sec^?1, ΔH

= 28·6 kcal/mole and ΔS

= ?7 eu; (E,Z,Z)+(Z,Z,Z) k(178°)= 1·53 × 10^?5 sec^?1 or (E,Z,Z) k(178°) = 2·13 × 10^?5 sec^?1, ΔH

= 32 kcal/mole, ΔS

= ?9 eu; cis-5,6-dimethyl-1,3-cyclohexadiene (1,5-H shift), k(178°) = 1·77 × 10^?5 sec^?1, ΔH

= 33 kcal/mole, ΔS

= ?7 eu; trans-5,6-dimethyl-1,3-cyclohexadiene (1,5-H shift), k(178°) = 7·7 × 10^?6 sec^?1, ΔH

= 36 kcal/mole, ΔS

= ?3 eu.     

Highly stereoselective synthesis of (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated esters and (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated amides from 1-bromo-1-fluoroalkenes via palladium-catalyzed carbonylation reactions

The highly stereoselective synthesis of (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated esters and (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated amides is described. 1-Bromo-1-fluoroalkenes (E/Z approximately 1:1), which are readily available starting materials, have been found to isomerize to high E/Z ratios after storage at -20 degrees C for 1 week or by photolysis at 254 nm. Since the (E)-isomers have been found to react faster than the corresponding (Z)-isomers at room temperature in Pd(0)-catalyzed reactions, the palladium-catalyzed carboalkoxylation of high E/Z 1-bromo-1-fluoroalkenes lead to a high Z/E (Z/E >/= 98:2) ratio of the alpha-fluoro-alpha,beta-unsaturated esters. When 1-bromo-1-fluoroalkenes (E/Z approximately 1:1) were reacted with HCOOH/NBu(3)/Pd(II)/DMF, the (E)-isomer was selectively reduced, and the remaining (Z)-1-bromo-1-fluoroalkenes were recovered in essentially pure isomeric form. The resulting mixture of (Z)-1-bromo-1-fluoroalkenes and the reduced products underwent similar palladium-catalyzed carboalkoxylation reactions at 70 degrees C, and the (E)-alpha-fluoro-alpha,beta-unsaturated esters were stereospecifically obtained. This methodology was also successfully applied for the stereospecific synthesis of (Z)- and (E)-alpha-fluoro-alpha,beta-unsaturated amides: the palladium-catalyzed carboamidation reaction of high E/Z and (Z)-1-bromo-1-fluoroalkenes lead to pure (Z)- and (E)-alpha-fluoro-alpha,beta-unsaturated amides, respectively.     

The mechanism of the acid-catalyzed decomposition of the farnesyl phosphates

The rates and (in some cases) products of the acid-catalyzed decomposition of (Z,E)- and (E,E)-farnesyl phosphate, (Z,E)- and (E,E) - 1,1 - dideutereofarnesyl phosphate, (Z)- and (E) - 6,7,10,11 - tetrahydrofarnesyl phosphate, and t-butyl phosphate have been studied in an attempt to determine whether (Z,E)-farnesyl phosphate ionizes with intramolecular assistance from the C-6/C-7 double bond or via an unassisted process leading to a simple allylic cation. Data in support of both possibilities are adduced, but it is concluded, primarily on the basis of the secondary deuterium kinetic isotope effects, that the ionization involves little, if any, assistance from the double bond.     

A facile synthesis of the sex pheromone of Grapholitha molesta

The sex pheromone of Grapholitha molesta, (Z/E)-8-dodecylen-1-ol acetate, was easily synthesized in an overall yield of 41.5% with 1,8-octanediol as starting material via mono-esterification, PCC oxidation, and Witting reactions. The Z/E ratio is 83:17. Configuration transformation of Z/E 83:17 compound with sodium nitrite and nitric acid resulted in the production of a compound with Z/E 24:76. The products were confirmed by IR, ¹H NMR, and MS spectral data.     

Stability of the normal, zwitterionic neutral and anionic forms of aspartic acid in gas phase and aqueous media

Aspartic acid has a place of special importance among amino acids in view of its property to racemize from the - to the -form in living and nonliving systems which can be used to determine age. Molecular geometries of two isomeric normal neutral forms (called A and B forms), isomeric zwitterionic neutral forms (called A(Z) and B(Z) forms) and anions of these forms of aspartic acid were optimized at the RHF/6-31+G^* level. The geometries of hydrogen bonded complexes of each of the above species with one, two and three water molecules were also optimized at the same level. All these systems were solvated in bulk water using the polarized continuum model (PCM) of the self-consistent reaction field (SCRF) theory at the RHF/6-31+G^* level using the gas phase optimized geometries. It is found that in gas phase, the normal neutral A and B forms of aspartic acid would coexist while the zwitterionic A(Z) and B(Z) forms of the same would be absent. On the other hand, in bulk aqueous media, the normal neutral A and B forms of aspartic acid would not occur while the zwitterionic A(Z) and B(Z) forms would be present. Further, the abundance of the A(Z) form would be much more than that of the B(Z) form in bulk water. If the solution pH is adjusted appropriately so that a monoanion is formed, the anion of aspartic acid obtained from the neutral zwitterionic form by deprotonating O₈ would occur dominantly.     

Co-doping a metal (Cr,Mn, Fe,Co, Ni,Cu, and Zn) on Mn/ZSM-5 catalyst and its effect on the catalytic reduction of nitrogen oxides with ammonia

Selective catalytic reduction (SCR) of NO_x by NH₃ over a series of Mn–M/Z catalysts (M = Cr, Mn, Fe, Co, Ni, Cu, Zn, and Z = the ZSM-5 Zeolite) synthesized by wet impregnation method was investigated. Mn–Fe/Z, Mn–Co/Z, and Mn–Cu/Z catalysts exhibited approximately 100 % NO_x conversion over a wide temperature range (200–360 °C) in a defined atmospheric condition, which was noticeably greater than that of Mn–Cr/Z (340–360 °C). Furthermore, the effect of addition of second metal oxide species to the initial Mn/Z catalyst on the structure of catalysts was studied by several characterization techniques. BET measurements revealed high surface area and pore volume of the Mn–Cu/Z catalyst. In addition, the XRD and UV–Vis DR results showed that addition of co-doped metal oxide species improved the dispersion of metal ions and inhibited crystallization of metal oxides. UV–Vis studies also were in good accordance with DTA/TG results confirming the formation of cobalt oxide and copper oxide clusters in Mn–Co/Z and Mn–Cu/Z catalysts, respectively. The FTIR spectra of pyridine adsorption, in addition, suggested the Mn–Cu/Z catalyst contained the most Lewis acid sites leading to more NO_x adsorption capacity.     

Layer-by-layer assembly of zeolite crystals on glass with polyelectrolytes as ionic linkers

ZSM-5 crystals and glass plates tethered with trimethylpropylammonium iodide and sodium butyrate, respectively, (denoted as Z+, Z-, G+, and G-, respectively) were prepared. Treatment of G- with Z+ suspended in ethanol results in monolayer assembly of Z+ on G- (G-/Z+) with high surface coverage. The zeolite crystals have a strong tendency to closely pack and align with the b-axis normal to the glass plate, despite large positive zeta potentials. Subsequent treatment of G-/Z+ with Z- leads to second-layer assembly of Z- on G-/Z+ (G-/Z+/Z-), but with rather poor coverage. Sequential treatment of G+ with poly(sodium 4-styrenesulfonate)(Na+PSS-), poly(diallyldimethylammonium chloride) (PDDA+Cl-), and Na+PSS- followed by Z+ yields glass plates assembled with monolayers of Z+ with very high surface coverage through the composite polyelectrolyte linkers (G+/PSS-/PDDA+/PSS-/Z+). The zeolite crystals also have a strong tendency to closely pack and align with the b-axis perpendicular to the substrate plane. The binding strength between the zeolite crystals and glass plates is much higher in G+/PSS-/PDDA+/PSS-/Z+ than in G-/Z+. Repetition of the sequential PSS-/PDDA+/PSS-/Z+ layering for five cycles yields glass plates assembled with pentalayers of ZSM-5 crystals [G+/(PSS-/PDDA+/PSS-/Z+)(5)]. The observed degrees of coverage and alignment of zeolite crystals in each layer were very high up to the third layers despite the nonuniformity of the sizes and shapes of the zeolite crystals used in this study. This report thus demonstrates the feasibility of layer-by-layer assembly of micrometer-sized zeolite crystals on glass through electrostatic interaction between surface-bound, full-fledged ionic centers, especially by use of polyelectrolyes as the linkers.     

Stereoselective preparation of (E)- and (Z)-alpha-fluorostilbenes via palladium-catalyzed cross-coupling reaction of high E/Z ratio and (Z)-1-bromo-1-fluoroalkenes

A highly stereoselective method to prepare both (E)- and (Z)-alpha-fluorostilbenes is described. 1-Bromo-1-fluoroalkenes (E/Z approximately 1:1), a readily available starting material, isomerizes to high E/Z ratios by storage at -20 degrees C or by photolysis at 254 nm. Stille coupling between these high E/Z 1-bromo-1-fluoroalkenes and aryl stannanes gave (Z)-alpha-fluorostilbenes in high stereoselectivity. (Z)-1-Bromo-1-fluoroalkenes, which were kinetically separated from 1-bromo-1-fluoroalkenes (E/Z approximately 1:1), can participate in Suzuki coupling reactions to give (E)-alpha-fluorostilbenes stereoselectively.     

Temperature investigations of E/Z isomers in ketimines based of p-dibenzoylobenzene with aniline and 2,6-dimethylaniline by infrared spectroscopy

The reaction of aniline with p-dibenzoylobenzene (K1) can lead to Z/Z, Z/E and E/E isomers however the only Z/Z and E/E were formed. At room temperature these isomers may be separated, thus the corresponding FTIR spectra could be recorded. The observed bands were assigned and temperature investigations were lead to monitor the structural changes during heating Z and E forms of K1 from 20 to 240 degrees C. FTIR spectroscopy showed that the bigger changes of the Z form was observed with an increase of temperature. Similar experience was lead with the ketimine synthesized from 2,6-dimethylaniline and p-dibenzoylobenzene (K2) investigated as a mixture of isomers.     

水稻二化螟拟信息素的合成

通过烷叉三苯基膦烷与脂肪醛或芳香醛的Wittjg反应,立体选择性地制备了(Z)-十六碳烯及其环氧化合物、芳基类似物,顺-5-十六碳烯经溴加成,氨基钠/液氨中退减-还原转变成反-5-十六碳烯,上述化合物对二化螟触角电位具有生物活性。     

Approximate scaling properties of the density functional theory Tc for atoms

Revealed are scaling properties for T(c)[rho], the kinetic-energy component of the correlation energy density functional for atoms, in terms of the total number of electrons N, the nuclear charge Z, and the total electron density at the nucleus rho(0). T(c) scales well as Nrho(0)/Z(8/3) for both neutral atoms up to Z=18 and the four-electron Be-like cationic species. A model is given that describes these findings, involving a density encoding the cusp information and an effective potential going like r(-4/3).     

Finite size scaling for the atomic Shannon-information entropy

We have developed the finite size scaling method to treat the criticality of Shannon-information entropy for any given quantum Hamiltonian. This approach gives very accurate results for the critical parameters by using a systematic expansion in a finite basis set. To illustrate this approach we present a study to estimate the critical exponents of the Shannon-information entropy S approximately (lambda-lambda(c))(alpha(S) ), the electronic energy E approximately (lambda-lambda(c))(alpha(E) ), and the correlation length xi approximately mid R:lambda-lambda(c)mid R:(-nu) for atoms with the variable lambda=1/Z, which is the inverse of the nuclear charge Z. This was realized by approximating the multielectron atomic Hamiltonian with a one-electron model Hamiltonian. This model is very accurate for describing the electronic structure of the atoms near their critical points. For several atoms in their ground electronic states, we have found that the critical exponents (alpha(E),nu,alpha(S)) for He (Z=2), C (Z=6), N (Z=7), F (Z=9), and Ne (Z=10), respectively, are (1, 0, 0). At the critical points lambda(c)=1/Z(c), the bound state energies become absorbed or degenerate with continuum states and the entropies reach their maximum values, indicating a maximal delocalization of the electronic wave function.     

亚洲玉米螟性信息素的简便合成

从Z-15-二十四碳烯酸(1)出发, 经关键中间体13-十四碳烯-1-醇醋酸酯(4)。以CoCl2-Ph3P-NaBH4为催化体系异构化合成亚洲玉米螟性信息素Z/E-12-十四碳烯-1-醇醋酸酯(5)。经GC测定, 其Z、E比例接近1:1。     

STUDIES ON PLANT BILE PIGMENTS. II. REGIOSELECTIVE PHOTOCHEMICAL AND ACID CATALYZED Z,E ISOMERIZATION OF DIHYDROBILINDIONE AS PHYTOCHROME MODEL

The (4 Z, 10 Z , 15 E )-2,3-dihydrobilindione 4 , along with the fully unsaturated ( E, Z, Z )-analogue 8 , has been prepared from the corresponding ( Z, Z, Z )-isomer by a variation of Falk's method (Falk et aL, 1980). The photochemical and acid-catalyzed back-reactions have been studied by UV-vis and ¹H-NMR spectroscopy.     

Cp2TiCl2及Cp2ZrCl2存在下炔烃还原偶联反应的区域选择性

经五元钛、锆杂环,由非对称炔烃,区域选择性地合成了一系列立体专一的(Z,Z)-四芳基-1,3-丁二烯,并通过物理、化学方法证明了产物结构.     

A comparative evaluation of biological activities and bioactive compounds of the seagrasses Zostera marina and Zostera noltei from southern Portugal

This work assessed the antioxidant potential, acetylcholinesterase (AChE) inhibition and the in vitro cytotoxic activity of extracts of the seagrasses Zostera marina and Zostera noltei collected from southern Portugal. The total phenolic contents (TPCs), the rosmarinic acid (RA) concentration (HPLC/DAD) and the fatty acid (FA) profile (GC/MS) are also described. Z. marina had the highest TPC, radical scavenging activity against DPPH radicals and copper chelating activity. Z. noltei had metal chelation capacity to copper and iron ions. None of the species was able to inhibit AChE. Both seagrasses had high levels of polyunsaturated FAs. Z. marina significantly and selectively reduced the viability of tumorous neuronal cells. Z. noltei was highly toxic for the three cell lines tested and was selective against hepatocarcinoma cells at the concentration of 100 μg/mL. RA was the main compound identified in Z. marina, but not in Z. noltei.     

Ab initio study of the substituent effects on the relative stability of the E and Z conformers of phenyl esters. Stereoelectronic effects on the reactivity of the carbonyl group

Equilibria between the Z (tau1= 0 degrees) and E (tau1= 180 degrees) conformers of p-substituted phenyl acetates 4 and trifluoroacetates 5 (X = OMe, Me, H, Cl, CN, NO2) were studied by ab initio calculations at the HF/6-31G* and MP2/6-31G* levels of theory. The preference for the Z conformer, DeltaE(HF), was calculated to be 5.36 kcal mol(-1) and 7.50 kcal mol(-1) for phenyl acetate and phenyl trifluoroacetate (i.e., with X = H), respectively. The increasing electron-withdrawing ability of the phenyl substituent X increases the preference of the Z conformer. An excellent correlation with a negative slope was observed for both series between DeltaE of the E-Z equilibrium and the Hammett sigma constant. By using an appropriate isodesmic reaction, it was shown that electron-withdrawing substituents decrease the stability of both conformers, but the effect is higher with the E conformer. Electron-withdrawing phenyl substituents decrease the delocalization of the lone pair of the ether oxygen to the C=O antibonding orbital (nO--> pi*C=O) in both the E and Z forms and in both series studied; this effect is higher in the E conformer than in the Z conformer. The nO --> pi*C=O electron donation has a minimum value with tau1= 90 degrees and a maximum value with tau1= 0 degrees (the Z conformer), the value with tau1= 180 degrees (the E conformer) being between these two values, obviously due to steric hindrance. The effects of the phenyl substituents on the reactivity of the esters studied are discussed in terms of molecular orbital interactions. ED/EW substituents adjust the availability of the pi*C=O antibonding orbital to interact with the lone pair orbital of the attacking nucleophile and therefore affect the reactivity: EW substituents increase and ED substituents decrease it. Excellent correlations were observed between the rate coefficients of nucleophilic acyl substitutions and pi*C=O occupancies of the ester series 4 and 5.     

Comparative study on the stabilities and properties of heterodimers containing the intermolecular interactions of CF2Cl2 with the isoelectronic and isostructure species of N2O and CO2

The computational investigations are carried out on the heterodimers containing CF₂Cl₂ with isoelectronic and isostructure (linear triatomics) species of N₂O and CO₂ through MP2/aug-cc-pV(D+d)Z, MP2/aug-cc-pV(T+d)Z//MP2/aug-cc-pV(D+d)Z, and CCSD(T)/aug-cc-pV(D+d)Z//MP2/aug-cc-pV(D+d)Z levels. Five and twelve heterodimers are located on the potential energy surface of CF₂Cl₂–CO₂ and CF₂Cl₂–N₂O systems, respectively. Binding energies of heterodimers in the CF₂Cl₂–CO₂ and CF₂Cl₂–N₂O systems corrected with BSSE are in the ranges of 1.30–5.79 and 1.30–6.85 kJ/mol at the MP2/aug-cc-pV(T+d)Z//MP2/aug-cc-pV(D+d)Z level, respectively. The calculated results reveal that the five most stable heterodimers among all heterodimers obtained for the CF₂Cl₂–CO₂ and CF₂Cl₂–N₂O systems belong to CF₂Cl₂–N₂O system. Therefore, CF₂Cl₂–N₂O system has more key role than CF₂Cl₂–CO₂ one in the atmosphere.