Cobalt-catalyzed intramolecular [2 + 2 + 2] cocyclotrimerization of nitrilediynes: an efficient route to tetra- and pentacyclic pyridine derivatives

[reaction: see text] In this paper, we wish to report the intramolecular [2 + 2 + 2] cocyclotrimerization of nitrilediynes catalyzed by the CoI2(dppe)/Zn system at 80 degrees C in CH3CN. Under these reaction conditions, various highly substituted nitrilediynes having steric conjunction at the alpha and beta positions to a nitrile group and a bulkier substitution at the terminal carbon of alkyne undergo [2 + 2 + 2] cocylotrimerization to afford tetra- and pentacyclic pyridine derivatives in good to excellent yields.     

Rearrangements and Hydration of 2-Ethynylisoborneol and 2-Ethynylisocamphanol

The reaction of 2-ethynylisoborneol with acetic acid in the presence of boron trifluoride-diethyl ether complex gave 4-ethynylisobornyl acetate as a result of successive skeletal rearrangements. Under the Kucherov reaction conditions 2-ethynylisoborneol underwent Meyer—Schuster rearrangement leading to (2-bornylidene)acetaldehyde. The hydration product of 2-ethynylisoborneol, 2-acetylisoborneol, was obtained by the action of mercury(II) acetate in dioxane under mild conditions. The Nieuwland reaction of 2-ethynylisoborneol afforded 4-acetylisoborneol acetate. 2-Ethynylisocamphanol in the presence of formic acid gave rise to a mixture of Rupe and Meyer—Schuster rearrangement products, stereoisomeric 2-(isocamphylidene)acetaldehydes and 2-acetylisocamphene. Mixtures of acetyl-substituted acetates having a camphane, isocamphane, and bicyclo[3.2.1]octane skeleton were obtained in the reaction with acetic acid in the presence of BF₃-Et₂O. Under the Nieuwland reaction conditions 2-ethynylisocamphanol underwent hydration and rearrangement with ring expansion, yielding a mixture of endo-2-hydroxy-2,6,6,7-tetramethylbicyclo[3.2.1]octan-3-one and the corresponding acetate.     

An Exploratory Flow Reactor Study of H2S Oxidation at 30–100 Bar

Hydrogen sulfide oxidation experiments were conducted in O₂/N₂ at high pressure (30 and 100 bar) under oxidizing and stoichiometric conditions. Temperatures ranged from 450 to 925 K, with residence times of 3–20 s. Under stoichiometric conditions, the oxidation of H₂S was initiated at 600 K and almost completed at 900 K. Under oxidizing conditions, the onset temperature for reaction was 500–550 K, depending on pressure and residence time, with full oxidization to SO₂ at 550–600 K. Similar results were obtained in quartz and alumina tubes, indicating little influence of surface chemistry. The data were interpreted in terms of a detailed chemical kinetic model. The rate constants for selected reactions, including SH + O₂ ⇄ SO₂ + H, were determined from ab initio calculations. Modeling predictions generally overpredicted the temperature for onset of reaction. Calculations were sensitive to reactions of the comparatively unreactive SH radical. Under stoichiometric conditions, the oxidation rate was mostly controlled by the SH + SH branching ratio to form H₂S + S (promoting reaction) and HSSH (terminating). Further work is desirable on the SH + SH recombination and on subsequent reactions in the S₂ subset of the mechanism. Under oxidizing conditions, a high O₂ concentration (augmented by the high pressure) causes the termolecular reaction SH + O₂ + O₂ → HSO + O₃ to become the major consumption step for SH, according to the model. Consequently, calculations become very sensitive to the rate constant and product channels for the H₂S + O₃ reaction, which are currently not well established.     

2-C-branched glycosides from 2'-carbonylalkyl 2-O-Ms(Ts)-C-glycosides. A tandem SN2-SN2 reaction via 1,2-cyclopropanated sugars

[reaction: see text] Under basic conditions, 2'-aldehydo (acetonyl) 2-O-Ms(Ts)-alpha-C-glycosides undergo an intramolecular S(N)2 reaction to form 1,2-cyclopropanated sugars, which react with nucleophiles (alcohols, thiols, and azide) at the anomeric carbon to give 2-C-branched glycosides. By way of contrast, the 1,2-cyclopropanes derived from 2'-ketones only react with thiols to give 2-C-branched thioglycosides.     

Classical and quantum-mechanical plane switching in CO2

Classical plane switching takes place in systems with a pronounced 1:2 resonance, where the degree of freedom with the lowest frequency is doubly degenerate. Under appropriate conditions, one observes a periodic and abrupt precession of the plane in which the doubly degenerate motion takes place. In this article, we show that quantum plane switching exists in CO(2). Based on our analytical solutions of classical Hamilton's equations of motion, we describe the dependence on vibrational angular momentum and energy of the frequency of switches and the plane switching angle. Using these results, we find optimal initial wave-packet conditions for CO(2) and show, through quantum-mechanical propagation, that such a wave packet indeed displays plane switching at energies around 10 000 cm(-1) above the ground state on time scales of about 100 fs.     

Phosphodiester cleavage of guanylyl-(3',3')-(2'-amino-2'-deoxyuridine): rate acceleration by the 2'-amino function

Hydrolytic reactions of the structural analogue of guanylyl-(3',3')-uridine, guanylyl-(3',3')-(2'-amino-2'-deoxyuridine), having one of the 2'-hydroxyl groups replaced with an amino function, have been followed by RP HPLC in the pH range 0-13 at 90 degrees C. The results are compared to those obtained earlier with guanylyl-(3',3')-uridine, guanylyl-(3',3')-(2',5'-di-O-methyluridine), and uridylyl-(3',5')-uridine. Under basic conditions (pH > 8), the hydroxide ion-catalyzed cleavage of the P-O3' bond (first-order in [OH(-)]) yields a mixture of 2'-amino-2'-deoxyuridine and guanosine 2',3'-cyclic phosphate which is hydrolyzed to guanosine 2'- and 3'-phosphates. Under these conditions, guanylyl-(3',3')-(2'-amino-2'-deoxyuridine) is 10 times less reactive than guanylyl-(3',3')-uridine. Under acidic and neutral conditions (pH 3-8), where the pH-rate profile for the cleavage consists of two pH-independent regions (from pH 3 to pH 4 and from 6 to 8), guanylyl-(3',3')-(2'-amino-2'-deoxyuridine) is considerably reactive. For example, in the latter pH range, guanylyl-(3',3')-(2'-amino-2'-deoxyuridine) is more than 2 orders of magnitude more labile than guanylyl-(3',3')-(2',5'-di-O-methyluridine), while in the former pH range the reactivity difference is 1 order of magnitude. Under very acidic conditions (pH < 3), the isomerization giving guanylyl-(2',3')-(2'-amino-2'-deoxyuridine) and depurination yielding guanine (both first-order in [H(+)]) compete with the cleavage. The Zn(2+)-promoted cleavage ([Zn(2+)] = 5 mmol L(-)(1)) is 15 times faster than the uncatalyzed reaction at pH 5.6. The mechanisms of the reactions of guanylyl-(3',3')-(2'-amino-2'-deoxyuridine) are discussed, particularly focusing on the possible stabilization of phosphorane intermediate and/or transition state via an intramolecular hydrogen bonding by the 2'-amino group.     

Walther reaction in the benzazoles series and preparation of their 2-deutero derivatives

Reactions of 2-hydrazino-substituted 1-methylbenzimidazole, benzothiazole, and benzoxazole with azobenzene at 160–180°C resulted in hydrazino group elimination and formation of the corresponding 2-H-benzazoles. Under similar conditions the 2-deuterohydrazinobenzazoles prepared from 2-hydrazinobenzazoles and heavy water were converted into 2-deuterobenzazoles.     

High pressure [4+2] and [2+2+2] reactions between cycloheptatriene and methyl propiolate

Under high pressure conditions, cycloheptatriene reacts with methyl propiolate to afford mono-, bis- and trisadducts all retaining, the norcaradiene structure. The four new compounds are formed via [4+21] and [2+2+2] cycloadditions. The latter are examples for the high pressure extension of the scope of homo-Diels-Alder reactions.     

Synthesis of 2-(2-hydroxyaroylmethylene)hexahydropyrimidines from 2-trichloromethylchromones and trimethylenediamine

The reactions of 2-trichloromethylchromones with trimethylenediamine in ethanol at room temperature afford 2-(2-hydroxyaroylmethylene)hexahydropyrimidines. Under analogous conditions, 2-methylchromone gives a mixture ofN,N′-trimethylenebis[3-amino-1-(2′-hydroxyphenyl)-2-buten-1-one] andN,N′-trimethylenebis(imine) of 2-hydroxyacetophenone. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2140–2143, November, 1999.     

微分脉冲伏安法同时测定3,4-二氢-2-羟基喹(口恶)啉和2-羟基喹(口恶)啉及研究其电极反应性质

以玻碳电极为工作电极,在pH为6的甲醇-B.R.缓冲溶液的混合溶液中,3,4-二氢-2-羟基喹噁啉在+0.48V有一氧化峰,2-羟基喹噁啉在-0.98V有一还原峰,峰高与相应的电活性物质浓度分别在2.8+10~(-6)—8.0×10~(-5)mol/L和8.0×10~(-6)—6.4×10~(-4)mol/L范围内有良好的线性关系。在此条件下,对样品中二者含量进行了同时测定。     

Efficient copper-free PdCl2(PCy3)2-catalyzed Sonogashira coupling of aryl chlorides with terminal alkynes

Under copper-free conditions and with Cs2CO3 as a base, PdCl2(PCy3)2 showed high catalytic activity for cross-coupling of electron-rich, electron-neutral, and electron-deficient aryl chlorides with a variety of terminal alkynes in DMSO at 100-120 degrees C affording internal arylated alkynes in good to excellent yields.     

Liquid-phase oxidation of 2-methoxy-p-cresol to vanillin with oxygen catalyzed by a combination of CoCl2 and N-hydroxyphthalimide

Liquid-phase oxidation of 2-methoxy-p-cresol to vanillin (4-hydroxy-3-methoxybenzaldehyde), in methanol, with molecular oxygen at atmospheric pressure as oxidant and a combination of cobaltous chloride and N-hydroxyphthalimide (NHPI) as catalyst, has been investigated. The effect of reaction conditions on conversion and selectivity for vanillin was studied systematically. Selectivity for vanillin could be enhanced by optimizing the molar ratio of 2-methoxy-p-cresol to NHPI, the amount of sodium hydroxide, reaction time, reaction temperature, and the volume of methanol, which determined the concentration of the reactants. Under the optimized conditions the yield of vanillin was 90.1 %.     

HYDROGENATION OF CO_2 OVER A YBa_2Cu_3O_(6～7) CATALYST

研究了ＹＢａＣｕ３Ｏ６～７超导催化剂上ＣＯ２的加氢制醇反应。考察了温度、压力和空速等条件对催化剂反应性能的影响。反应的主要产物是甲醇、ＣＯ和少量甲醚。利用ＸＰＳ、ＸＲＤ和ＡＦＭ等技术对催化剂的结构、铜的存在状态和反应活性位进行表征发现，在反应过程中，ＹＢａ２Ｃｕ３Ｏ６～７由ｏｒｔｈｏｍｂｉｃ相转变为ｔｅｔｒａｇｏｎａｌ相。反应活性位可能是Ｃｕ（Ｉ）物种。反应后催化剂颗粒的分散程度明显提高     

WO3/SiO2催化剂上2-丁烯与乙烯歧化制丙烯

采用浸渍法制备了WO₃/SiO₂催化剂,对其进行了UV-Vis DRS和NH₃-TPD表征。将WO₃/SiO₂作为催化剂,以乙烯和2-丁烯为原料制备丙烯,考察了反应温度、质量空速等因素对歧化反应的影响。实验结果表明,催化剂的最佳WO₃担载量为8 %;以8%WO₃/SiO₂ 为催化剂,在反应温度473K~573K、压力3.0MPa、质量空速1.6h^-1下,2-丁烯的转化率可保持在80%以上,丙烯的选择性大于89.2%。经过140h的稳定性实验,2-丁烯的转化率和丙烯的选择性略有下降,适当的提高反应温度（由473K增加到513K）可以恢复催化剂的活性。新鲜催化剂表面存在四面体、八面体六价钨物种和体相WO₃,适当还原的W物种是歧化活性物种;W负载在催化剂表面引入了新的强酸中心,同时明显增加了总酸量。     

Synthesis of 2, 2, 5, 5-tetramethyltetrahydrothiophene

Under the conditions of the Grignard reaction, 2, 5-dimethyl-2, 5-hexanediol has been obtained from diethyl succinate. Under the action of sulfuric acid, the latter has been cyclized to 2, 2, 5, 5-tetramethyl-tetrahydrofuran which, in its turn, by treatment with phosphorus pentasulfide, has given 2, 2, 5, 5-tetramethyltetrahydrothiophene. Its reaction with methyl iodide has given 2, 2, 5, 5-tetramethyltetrahydrothiophene methiodide.     

Tautomerization of 2-acetylcyclohexanone. 1. Characterization of keto-enol/enolate equilibria and reaction rates in water

The keto-enol tautomerism of 2-acetylcyclohexanone (ACHE) was studied in water under different experimental conditions. By contrast with other previously studied beta-diketones, the keto-enol interconversion in the ACHE system is a slow process. Under equilibrium conditions, the analysis of the absorbance readings of ACHE aqueous solutions yielded more than 40% of enol content at 25 degrees C; nevertheless, in aprotic solvents such as dioxane, ACHE is almost completely enolized. In alkaline medium, the enolate ion is the only existing species; the study of the effect of pH on the UV-absorption spectrum of ACHE yielded a value of 9.85 for the overall pK(a) of ACHE. Under nonequilibrium conditions, the keto-enol tautomerization was studied in water. Several factors affecting the reaction have been investigated, which include H(+)-catalysis, ionic strength effect, buffer catalysis, deuterium isotope effects, temperature effect, or solvent effects.     

Direct and continuous synthesis of concentrated hydrogen peroxide by the gaseous reaction of H2/O2 non-equilibrium plasma

Under ambient conditions, H2O2 has been synthesized with 32.51% yield and 56.25% selectivity via the gas-phase reaction of H2/O2 non-equilibrium plasma.     

方铁锰矿Mn2O3粉体的水热合成与表征

方铁锰矿型 Mn2 O3是固相法合成锂离子二次电池正极材料 L i Mn2 O4 的最佳原料之一 [1] .以其为锰源 ,可以很容易地制备锂离子二次电池正极材料 L i Mn2 O4 尖晶石 .采用其它合成方法都难以得到方铁锰矿 Mn2 O3的纯相 ,而是得到含有 α,β和 γ型的混合相 ,这对合成性能优良的正极材料 L i Mn2 O4极为不利[2 ] .采用水热合成法不仅可以人工合成沸石 ,而且已广泛用于合成多种无机功能材料[3～ 5] .无机原位氧化还原沉淀水热合成法 [6 ]可使多步反应的分子在原位水平上进行接触和反应 ,分子的扩散自由程大大缩短 ,因而降低了扩散的时间…     

Palladium-catalyzed furylation and thienylation of activated alkenes with 2-furoyl chloride and 2-thenoyl chloride

2-Furoyl or 2-thenoyl chlorides readily react with activated alkenes in the presence of a tertiary amine and a catalytic amount of palladium(II) acetate to give 2-furylated or 2-thienylated alkenes. Under similar conditions, 2-benzofuroyl chloride undergoes facile alkenylation to produce 2-alkenylated benzofurans. The reaction involves a highly efficient decarbonylation of furoyl or thenoyl-palladium species.     

Versatile synthesis of quinoline-3-carboxylic esters and indol-2-acetic esters by palladium-catalyzed carbonylation of 1-(2-aminoaryl)-2-yn-1-ols

1-(2-Aminoaryl)-2-yn-1-ols, easily obtained by the Grignard reaction between 1-(2-aminoaryl)ketones and alkynylmagnesium bromides, were subjected to carbonylative conditions in the presence of the PdI2-KI catalytic system, in the presence and in the absence of an external oxidant. Under oxidative conditions (80 atm of a 4:1 mixture of CO-air, in MeOH as the solvent at 100 degrees C and in the presence of 2 mol % of PdI2 and 20 mol % of KI), 1-(2-aminoaryl)-2-yn-1-ols bearing a primary amino group were selectively converted into quinoline-3-carboxylic esters in fair to good yields [45-70%, based on starting 1-(2-aminoaryl)ketones], ensuing from 6-endo-dig cyclization followed by dehydration and oxidative methoxycarbonylation. On the other hand, indol-2-acetic esters, deriving from 5-exo-dig cyclization followed by dehydrating methoxycarbonylation, were selectively obtained in moderate to good yields [42-88%, based on starting 1-(2-aminoaryl)ketones] under nonoxidative conditions (90 atm of CO, in MeOH as the solvent at 100 degrees C and in the presence of 2 mol % of PdI2 and 20 mol % of KI), in the case of 1-(2-aminoaryl)-2-yn-1-ols bearing either a primary or secondary amino group and substituted with a bulky group on the triple bond.