Highly efficient synthesis of linear pyrrole oligomers by twofold Heck reactions

The twofold Heck reaction of the vinylpyrroles 3a and 3b with the iodobenzenes 4a-c led to the linear pyrrole oligomers 5, 6, and 7. The synthesis of both symmetrical and unsymmetrical oligomers, such as 10a and 10b, was also accomplished by a Heck reaction of 8 and 9 and by a Heck reaction of 3a and 11 followed by a Wittig reaction and a second Heck reaction with 8. The pentacyclic oligomers 14 and 19 were prepared by a twofold Heck reaction of 13 with 4 and by a twofold Heck reaction of 15 with 16 followed by a Wittig reaction and a twofold Heck reaction with 8.     

Chemically amplified current response of vitamin C based on the cyclic reaction between l-ascorbic acid and dehydroascorbic acid, using dithiothreithol and ascorbate oxidase

A cyclic reaction between the reduced and the oxidized forms of vitamin C takes place by combining the ascorbate oxidase reaction and the reduction of l-ascorbic acid to dehydroascorbic acid by dithiothreithol. l-Ascorbic acid is oxidized by the dissolved oxygen and its consumption is not compensated by the chemical regeneration of l-ascorbic acid from dehydroascorbic acid. The dissolved oxygen then continues to decrease during the cyclic reaction, consequently, the decrease of the reduction current of oxygen is amplified. The amplification factor of 5 x 10(-5)Ml-ascorbic acid at 5 x 10(-3)M dithiothreithol and pH 7.5 was found to be 10.6 when enzyme activity is 0.64 units/ml and the reaction time is 10 min.     

Highly stereoselective and modular syntheses of 10-hydroxytrilobacin and three diastereomers via stereodivergent [3 + 2]-annulation reactions

A convergent synthesis of the annonaceous acetogenin, 10-hydroxytrilobacin ( 4a), was accomplished by using the [3 + 2]-annulation reaction of tetrahydrofuranyl carboxaldehyde 2a and allylsilane 3. The stereodivergency of the [3 + 2]-annulation reaction made it possible to achieve modular, highly stereoselective syntheses of three 10-hydroxytrilobacin diastereomers from the same precursors by using simple modifications of reaction conditions.     

Reaction of ethyl 9-thioacridonyl-10-acetate with hydrazine

The reaction of ethyl 9-thioacridonyl-10-acetate with hydrazine hydrate gives the corresponding ethyl hydrazonoacridonyl-10-acetate, which readily undergoes a reaction with aldehydes and on heating in DMF reacts with hydrazine hydrate to form 9-ylidenehydrazonoacridonyl-10-acetic acid hydrazide. The latter undergoes a condensation reaction with aldehydes to form ylidenehydrazides of acridonyl-10-acetic acid 9-ylidenehydrazones. The structures of these compounds have been confirmed by UV, IR, PMR, and mass spectrometry.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 525–527, April, 1989.     

SnO2/CeO2表面反应速率方程和分子反应几率

The principle and experimental law of testing sets to test reaction temperature change were introduced. Using “powder sputtering plane thin-film SnO2/CeO2 alcohol sensor”, the reaction temperature change was tested and the law of versus gas concentration was given by the inserting method. The rate equation of surface reaction was deduced and reaction probability of surface molecule was calculated. The general reaction rate equation includes two kinds of experiential formula—hyperbolic and power function formula and the concept of molecule reaction probability is minor, which in general is 10-3-10-5.     

In situ formation of dispersed palladium nanoparticles in microemulsion: efficient reaction system for ligand-free Heck reaction

The ligand-free Heck reaction catalyzed by Pd(OAc)2 performed well in a TX10 oil-in-water microemulsion. TEM proved in situ formation distributed palladium nanoparticles in the microemulsion. The role of TX10 in the reaction system is the palladium nanoparticles reducing agent and stabilizer. The effect of reaction parameters on the Heck reaction conversion were discussed. The results indicated that the aqueous phase concentration, the base concentration, and the temperature played key roles in the conversion of the reaction. Iodobenzene was converted to the corresponding trans-stilbene quantitatively within 90-150 min. Therefore, the heptane/TX 10/butanol/water/propylene glycol microemulsion containing in situ formed palladium nanoparticles was a very efficient catalyst system for the ligand-free Heck reaction.     

An efficient carbapenem synthesis via an intramolecular Wittig reaction of new trialkoxyphosphorane-thiolesters

New trialkoxyphosphorane-thiolesters 10, obtained by reaction of oxalimides 9 with trialkyl phosphite, were efficiently cyclized by an intramolecular Wittig reaction to give carbapenems 11.     

Temperature dependence of the rate coefficients for the reactions of Br atoms with dimethyl ether and diethyl ether

The rate constants for the reactions of atomic bromine with dimethyl ether and diethyl ether were measured from approximately 300 to 350 K using the relative rate method. Both isooctane and isobutane were used as the reference reactants, and the rate constants for the reactions of these hydrocarbons were measured relative to each other over the same temperature range. The kinetic measurements were made by photolysis of dilute mixtures of bromine, the reference reactant, and the test reactant in mixtures of argon and oxygen at a total pressure of 1 atm. The resulting ratios of rate constants were combined with the absolute rate constant as a function of temperature for the reference reaction of Br with isobutane to calculate absolute rate constants for the reactions of Br with isooctane, dimethyl ether, and diethyl ether. The absolute rate constant, in the units cm3 molecule(-1) s(-1), for the reaction of Br with dimethyl ether was given by k = (3.8 +/- 2.4) x 10(-10) exp(-(3.54 +/- 0.21) x 10(3)/T) while for the reaction of Br with diethyl ether the rate constant is given by k = (2.8 +/- 2.7) x 10(-10) exp(-(2.44 +/- 0.32) x 10(3)/T). On the same basis, the rate constant for the reaction of Br with isooctane is given by k = (3.34 +/- 0.59) x 10(-12) exp(-(1.80 +/- 0.11) x 10(3)/T). In each case, the activation energy of the reaction is significantly smaller than the endothermicity of the reaction. This is discussed in terms of a complex mechanism for these reactions.     

4-(4-β-D-吡喃阿洛糖苷-苯基)-2-芳基-5-氰基-6-甲氧基吡啶的合成及镇静活性研究

以豆腐果苷为原料,与4-取代苯乙酮发生Schmidt-Claisen反应,得到一系列查儿酮结构的E-4-β-D-吡喃阿洛糖苷-苯乙烯基-4-取代苯乙酮衍生物3a-3h,其中3c、3e、3f为新化合物。 3a-3h在甲醇钠存在下,与1,3－丙二氰发生1,4-Michael加成,经关环、重排、氧化,得到4-(4-β-D-吡喃阿洛糖苷-苯基)-2-芳基-5-氰基-6-甲氧基吡啶系列豆腐果苷衍生物10a-10h,联氨催化还原10e而得到10i。共获得十二个未见文献报道的新化合物,其结构经1H NMR、IR和HRMS确证,并进行了药理活性筛选,结果表明,部分化合物具有比母体化合物更好的镇静催眠活性。同时,本文对Schmidt-Claisen反应存在的主要副反应进行了分析;对查儿酮与1,3－丙二氰在甲醇钠存在下反应生成吡啶衍生物反应机理进行了推导,提出了氧化脱氢形成吡啶的新机理。     

Dienone Tautomers of 4-Alkoxy-2,6-di-tert-butylphenols

Generation and isolation of 4-alkoxycyclohexa-2,5-dienones 9, the tautomeric forms of the title phenols (10), is described. They are generated efficiently by the Ag ion mediated reaction of 4-bromocyclohexa-2,5-dienone 3b with simple alcohols, although they can be irreversibly isomerized into 10 under the reaction conditions. Crude materials with high amounts of 9 can be obtained by conducting the reaction with AgClO(4) in the presence of Na(2)CO(3) or with AgOCOCF(3) and by interrupting the reaction shortly after the formation of 9 is complete. The AgOCOCF(3) reaction produces labile 4-(trifluoroacetoxy)cyclohexa-2,5-dienone 11 also, the formation of which becomes significant as the alcohol becomes bulky. All of 9 prove to be very much susceptible to the prototropic rearrangement into 10 by catalysis with base, acid, or SiO(2). Crude dienones 9 can be conveniently prepared directly from phenol 6 by treatment for a short time with Br(2) in alcohols containing AgClO(4) and Na(2)CO(3). A one-pot synthesis from 6 of 4-oxyfunctionalized 2,6-di-tert-butylphenols, including 10, is also described.     

Furopyridines. XV . Synthesis and properties of ethyl 2-(3-furo[2,3-b]-, -[3,2-b]-, -[2,3-c]- and -[3,2-c]pyridyl)acetate

Ethyl 2-(3-furopyridyl)acetates 10a-d were synthesized from furopyridin-3(2H)-ones 4a-d by the Wittig-Horner reaction with diethyl cyanomethylphosphonate, hydrolysis and the subsequent esterification. Reaction of compounds 10a-d with lithium diisopropylamide (IDA) gave the corresponding methylene-lithiated intermediate, and the subsequent reaction with benzaldehyde, acetone and iodomethane afforded the methylene-alkylated product respectively, while N,N-dimethylacetamide did not give any reaction product. The 2-position of 10a, b and d is alkylated by the lithiation with excess of LDA and the successive reaction with an electrophile.     

Anti-addition mechanism in the intramolecular hydroalkoxylation of alkenes catalyzed by PVP-stabilized nanogold

(1R*,4S*,4aR*,9aS*,10S*)-10-Hydroxy-10-phenyl-1,4a,9a,10-tetrahydro-1,4-methanoanthracen-9(4H)-one (1c) was prepared for the elucidation of the reaction mechanism of intramolecular hydroalkoxylation of alkenes catalyzed by gold nanoclusters stabilized by a hydrophilic polymer, poly(N-vinyl-2-pyrrolidone) (Au:PVP). It was found that the reaction proceeded via anti-addition of alcohol to the alkene assisted by p-activation of the gold clusters, which is the same mechanism as the hydroamination by toluenesulfonamides.     

Isotope exchange in disulfur monoxide-water charged complexes: A mass spectrometric and computational study

A hitherto unknown, isotope-exchange reaction is studied in ionized gaseous mixtures containing disulfur monoxide and water. The kinetics, mechanism, and intermediate of the reaction are investigated by experimental and theoretical methods. The reactivity of the S(2)O(*+) cation with water is investigated under a wide range of pressures ranging from 10(-7) to 10(-4) Torr, by FT-ICR, TQ, and high-resolution CAD mass spectrometry. In the high-pressure limit the reaction proves to be a route to strongly bound sulfur-containing species.     

The effects of ultrasound frequency and power on the activation energy in Si-KOH reaction system

The activation energy is the minimum amount of energy required to initiate a reaction. It is one of the important indexes for appraising a reaction. The chemical reaction rate is closely related to the value of activation energy, and reducing activation energy is propitious to promoting a chemical reaction. In the present paper, the relationship between the activation energy in Si-KOH reaction system and the ultrasound frequency and power has been discussed for the first time. The range of ultrasound frequency and power is 40-100kHz （interval by 20kHz） and 10-50W （interval by 10W）, respectively. The experimental clata indicate that the activation energy decreases with the increasing ultrasound power. Comparing with the activation energy without ultrasound irradiation, the results in our paper indicate that ultrasound irradiation could reduce the activation energy in Si-KOH reaction system and increase the reaction rate.     

Stereoselective 4-benzyloxybut-2-enylation of aldehydes via an allyl-transfer reaction using a chiral allyl donor

[reaction: see text] A direct and highly stereoselective (E)-4-benzyloxybut-2-enylation of aldehydes was successfully carried out to give 5-benzyloxyhomoallylic alcohol (11) via an allyl-transfer reaction using a chiral allyl donor (10). The chiral allyl donor (10) was prepared by catalytic Sharpless asymmetric epoxidation of 3-methylbut-2-en-1-ol, followed by a stereospecific vinyl Grignard reaction of the epoxide in the presence of CuBr and selective benzylation of the primary alcohol of diol.     

新型1,4-二苯并二氮杂酮类衍生物的合成及其抗癌活性

以取代邻硝基苯甲酸为起始原料,与二氯亚砜反应制得邻硝基苯甲酰氯,再与苯胺在碱性条件下反应制得酰胺衍生物(6a~6d);以醋酸钯为催化剂,6a~6d经NBS溴代制得溴代衍生物(7a~7d); 7a~7d依次经N-烷基化反应,还原反应和分子内C-N键环合反应合成了10个新型的1,4-二苯并二氮杂酮类化合物(10a~10j),产率61%~78%,其结构经¹H NMR, ¹³C NMR和HR-MS(ESI)表征。初步体外活性测试结果表明:10a~10j对非小细胞肺癌细胞（A549）,人乳腺癌细胞（MDA-MB-231）和宫颈癌细胞(HeLa)均有抑制作用。其中,10g和10i对A549, 10g对MDA-MB-231, 10h和10i对HeLa的抑制率大于50%。     

Ion radicals. 40. Formation of 10-phenylphenothiazine 5-oxide and Nitro-10-phenylphenolhiazirie 5-oxides by reaction of 10-phenylphcnolhiazine cation radical perchlorate with nitrite ion

The reaction of 10-phenylphenolhiazine cation radical ( 1 ) with nitrite ion leads not only to 10-phenylphenothiazine 5-oxide ( 2 ) but also to 3-nitro-10-phenylphenothiazinc 5,5-dioxide ( 4 ), and two dinitro-10-phenylphenolhia/.ine 5-oxidcs ( 5 and 6 ). The products ( 3-6 ) appear to he formed from the nitration of 2 by nitrogen dioxide, the nitrogen dioxide arising from the reaction of nitric oxide (formed along with 2 when 1 reacts with nitrite anion) and oxygen.     

Recombination of the hydrated electron at high temperature and pressure in hydrogenated alkaline water

Pulse radiolysis experiments were performed on hydrogenated, alkaline water at high temperatures and pressures to obtain rate constants for the reaction of hydrated electrons with hydrogen atoms (H* + e-(aq) --> H(2) + OH-, reaction 1) and the bimolecular reaction of two hydrated electrons (e-(aq) + e-(aq) --> H(2) + 2 OH-, reaction 2). Values for the reaction 1 rate constant, k(1), were obtained from 100 - 325 degrees C, and those for the reaction 2 rate constant, k(2), were obtained from 100 - 250 degrees C, both in increments of 25 degrees C. Both k(1) and k(2) show non-Arrhenius behavior over the entire temperature range studied. k(1) shows a rapid increase with increasing temperature, where k(1) = 9.3 x 10(10) M(-1) s(-1) at 100 degrees C and 1.2 x 10(12) M(-1) s(-1) at 325 degrees C. This behavior is interpreted in terms of a long-range electron-transfer model, and we conclude that e-aq diffusion has a very high activation energy above 150 degrees C. The behavior of k(2) is similar to that previously reported, reaching a maximum value of 5.9 x 10(10) M(-1) s(-1) at 150 degrees C in the presence of 1.5 x 10(-3) m hydroxide. At higher temperatures, the value of k(2) decreases rapidly and above 250 degrees C is too small to measure reliably. We suggest that reaction 2 is a two-step reaction, where the first step is a proton transfer stimulated by the proximity of two hydrated electrons, followed immediately by reaction 1.     

MECHANISMS OF THE PHOTOSENSITIZED OXIDATION OF TYRAMINE

Abstract— …According to the criteria of enhancement in D₂O and inhibition by sodium azide, the oxidation of tyramine photosensitized by methylene blue is largely a singlet oxygen or Type II process. Its quantum yield approximates 0.3 in D₂O at pH 10. There is a less efficient reaction not quenched by azide, which is assigned to a dye-substrate or Type I process. It gives rise to products with distinct bands at 320 and 285nm. Products of the Type I reaction are further oxidized by singlet oxygen and thereby compete with tyramine for this reagent. Kinetic parameters were estimated by computer simulation of the dependence of quantum yield on extent of reaction. The rate constant for reaction of O₂ (¹Δ_g) with tyramine was estimated to be 2.8 × 10⁸ M ^-1 s ^-1± 20% at pH 10. The reaction was also sensitized by hypericin in what appears to be a Type II process.     

苯丙烯酸对松节油转化水合萜二醇的作用研究

本文对苯丙烯酸在松节油转化成水合萜二醇反应中的作用进行了对比研究。结果表明，在传统的２７％Ｈ２ＳＯ４催化，平平加，ＯＰ－１０，吐温－８０及吐温－８０￣吐温－２０混合剂分别作乳化剂的松节油水合反应中，加入苯丙烯酸可使水合萜二醇的收率提高８￣１０％，反应时间缩短４－７小时，本文还对产物及副产物作了质谱分析。