Microwave assisted IMDAF# reaction: Microwave irradiation applied with success to cycloaddition reaction of N-propargyl-N-p-tolyl-N-2-furfurylamines

The new tertiary furfurylamine with triple bond as a dienophylic part i. e. N-(5-methyl-2-furfuryl)-N-prop-2-ynyl-p-toluidine (1) was prepared and the intramolecular Diels-Alder reaction of the amine (1) was performed under microwave irradiation conditions and by heating a benzene solution of the amine under nitrogen. Comparing the results of the usual thermal and the MAOS reaction, we confirmed our expectations that MAOS could promote the outcome of IMDA reaction of the suitably N-substituted tertiary 2-furfuryl-amines. In the present example, N-p-tolyl-5-methyl-5,7a-dihydro-5,7a-epoxyisoindoline was obtained in much better yield and of higher purity.The acronym for: Intramolecular Diels-Alder Reaction of Furan.The acronym for: Microwave-Assisted Organic Synthesis.     

Modification of Poly(4-Methyl-2-Pentyne) in Supercritical Fluid Medium for Production of CO<Subscript>2</Subscript>-Selective Gas-Separation Membranes

The work is devoted to exploring the possibility of using supercritical fluids as media for modification of polymers offering promise for production of gas-separation membranes with the goal to improve selectivity towards CO₂. The possibility is demonstrated for introduction of fragments of quaternary ammonium salts into the structure of poly(4-methyl-2-pentyne) with the help of a two-stage process: bromination of the initial polymer with N-bromosuccinimide followed by the addition of the tertiary amine—N-butylimidazol— conducted in supercritical fluids as a medium. The use of trifluoromethane as the reaction medium provides the highest degree of modification of the brominated polymer with the amine. The polymer produced under the optimized conditions demonstrates a threefold increase of the calculated selectivity of separation of CO₂ and N₂ in comparison with the initial poly(4-methyl-2-pentyne).     

Synthesis and Characterization of 8-hydroxyquinoline Complexes of Tin(IV) and Their Application in Organic Light Emitting Diode

A series of 8-hydroxyquinoline complexes of tin, Q(2)SnCl(2) (Q?=?2-methyl-8-hydroxyquinoline, 8-hydroxyquinoline, 5,7-dibromo-8-hydroxyquinoline, 5-chloro-8-hydroxyquinoline, 5,7-dichloro-8-hydroxyquinoline and 5-nitro-8-hydroxyquinoline) were prepared by reacting stannous dichloride with 8-hydroxyquinoline and its derivatives. All complexes were characterized by elemental analysis, mass spectrometry and infrared, UV-vis and (1)H NMR spectroscopes. Furthermore, the molecular structure of a representative complex, dichlorido-bis(5-nitro-quinolin-8-olato-2N,O)tin(IV), was determined by single-crystal X-ray diffraction. The photoluminescence (PL) properties of all prepared compounds and electroluminescence (EL) property of a selected complex (Q?=?5-chloro-8-hydroxyquinoline) were investigated. The results showed that the emission wavelength can be tuned by electron donating or withdrawing group substituent on 8-hydroxyquinoline. Application of prepared complexes in fabrication of an OLED has been demonstrated.     

A novel and convenient synthesis of 4-hydroxy-6-methyl-3-(1-(phenylimino) ethyl)-2H-pyran-2-one derivatives under ultrasound irradiation

A facile, efficient and environment-friendly protocol for the synthesis of 4-hydroxy-6-methyl-3-(1-(phenylimino)ethyl)-2H-pyran-2-one derivatives has been developed by the convenient ultrasound-mediated condensation of amine with dehydroacetic acid. This method provides several advantages over current reaction methodologies including a simple work-up procedure, shorter reaction times and higher yields.     

Base‐dependent selectivity of an SNAr reaction

A detailed kinetic analysis and computational study of an S_NAr reaction between 2,5,6‐trifluoronicotinonitrile, 2 , and the ambident 3‐isopropoxy‐1H‐pyrazol‐5‐amine, 3 , is presented. The selectivity with respect to the reaction at the primary amino group of 2 , to give the desired product, 2,5‐difluoro‐6‐[(3‐isopropoxy‐1H‐pyrazol‐5‐yl)amino]nicotinonitrile, 1 , is strongly dependent upon reaction conditions. Reaction is found to proceed via both uncatalysed and base catalysed routes, and selectivity towards 1 is strongly enhanced in the presence of the base diazabicyclo[2,2,2]octane (DABCO). Computational studies in tetrahydrofuran solution at the B3LYP/6‐31G* level of theory have provided valuable insight into alternative kinetically indistinguishable reaction pathways. The results suggest that for reaction at the primary amino group, proton removal by DABCO accompanying amine addition allows avoidance of a high‐energy, zwitterionic Meisenheimer intermediate. Reactions at the alternative pyrazole nitrogen atoms are less sensitive to the presence of base because of stabilisation of the Meisenheimer zwitterions by intramolecular hydrogen bonding. Copyright © 2010 John Wiley & Sons, Ltd.     

Kinetic and mechanistic study of the atmospheric reaction of MBO331 with Cl atoms

The present work deals with the reaction of 3-methyl-3-buten-1-ol (MBO331) with Cl atoms, which has been investigated by gas chromatography with flame ionization detection (GC-FID) at atmospheric pressure in N₂ or air, using the relative rate technique. The rate constant reaction at 298?±?1?K was found to be (5.01?±?0.70)?×?10^?10?cm³ molecule^?1?s^?1, using cyclohexane, octane and 1-butene as a reference compounds. The temperature dependence for the reaction was studied within the 298?333?K range. Additionally, a product identification under atmospheric conditions has been performed for the first time by GC-MS, with 3-methyl-3-butenal, methacrolein and chloroacetone being observed as degradation products. A theoretical study on the reaction at the QCISD(T)/6-311G**//MP2/6-311G** level was also carried out to obtain more information on the mechanism. From the theoretical study it can be predicted that Cl addition to the double bond proceeds through lower energy barriers than H-abstraction pathways and therefore is energetically favoured. Finally, atmospheric implications of the results obtained are discussed.     

Role of hydrogen migration in the mechanism of acetic acid elimination from MH(+) ions of acetates on chemical ionization and collision-induced dissociation

The elimination of acetic acid from the MH(+) ions of acetates of stereoisomeric 2-methyl-1-cyclohexanols and 1-hydroxy-trans-decalins exhibits a significant degree of stereospecificity under isobutane chemical ionization and collision-induced dissociation (CID) conditions, resulting in more abundant [MH - AcOH](+) ions in the cis-isomers 4c and 5tc than in their trans-counterparts 4t and 5tt. These findings suggest the involvement of a 1,2-hydride shift from the beta- to the alpha-position in the course of the acetic acid elimination from the MH(+) ions of the above cis-acetates, resulting in tertiary carbocation structures. The proposed mechanism of the elimination is supported by a considerable deuterium isotope effect detected in beta-deuterium-labeled cis-2-methyl-1-acetoxycyclohexane and by a CID study of the structures of the [MH - AcOH](+) ions obtained from cis- and trans-1,2-diacetoxycyclohexanes. Copyright 1999 John Wiley & Sons, Ltd.     

Nucleophile‐electrophile interactions in the reaction of oxiranes with carboxylic acids in the presence of tertiary amines

The nucleophile‐electrophile interactions in the reaction system “N,N‐dimethylaniline – acetic acid – epichlorohydrin” have been investigated using kinetic methods and computer modeling. The observed orders of reactions have been determined for the overall reaction as well as for individual stages. The kinetic equations have been proposed; the activation parameters of the reactions have been evaluated. The behavior of the initial (amine) and intermediate (carboxylate) nucleophiles has been detailed in reaction pathway. Amine reacts with oxirane activated by acidic reagent while carboxylate‐anion—with both activated and nonactivated epichlorohydrin. The mechanism of oxirane ring opening by acid reagent in the presence of tertiary amine has been proposed, which comprise parallel‐consecutive compensation stages of reaction product formation. It has been demonstrated that the observed reaction order with respect to acid reactant depends upon the nature of electrophilic reagent (activated/nonactivated oxirane) and the ratio of the rates of compensation stages.     

A convenient ultrasound-promoted regioselective synthesis of fused polycyclic 4-aryl-3-methyl-4,7-dihydro-1H-pyrazolo[3,4-b]pyridines

Fused polycyclic 4-aryl-3-methyl-4,7-dihydro-1H-pyrazolo[3,4-b]pyridines were obtained in a three-component regioselective reaction of 5-amino-3-methyl-1H-pyrazole, 2H-indene-1,3-dione and arylaldehydes in ethanol under ultrasound irradiation. This rapid method produced the products in short reaction times (4–5 min) and excellent yields (88–97%).     

硫醚与2-甲基-1,5-己二烯反应的机理研究

采用密度泛函理论对硫醚与2-甲基-1,5-己二烯的反应机理进行了详细的理论探究.计算结果表明,该反应历程主要包含活性物种的生成、2-甲基-1,5-己二烯的插入、另一分子的硫醚的碳氢键活化三部分.在2-甲基-1,5-己二烯插入步骤中,发现其采用6-5-re-插入时需要克服的活化能垒最低,反应时更为占优,在进行烯烃分子内碳碳双键插入完成闭环反应时相对比较容易.通过能量对比探明硫醚的C-H键活化需要克服的能垒最高,为该反应的速控步.     

Parallel synthesis of 1,2,4-triazole derivatives using microwave and continuous-flow techniques

Abstract  

An efficient and convenient solution-phase synthesis of a 1H-1,2,4-triazole library with potential agrochemical activity is reported employing microwave-assisted organic synthesis (MAOS) and continuous-flow microfluidic synthetic methods starting from commercially available 3,5-dibromo-1H-1,2,4-triazole (1). MAOS was used for the synthesis of 5-amino-3-bromo-1,2,4-triazole analogs 3 and for their 3-aryl derivatives 4 via Suzuki–Miyaura coupling with polymer-supported catalyst. A microfluidic hydrogenation reactor integrated into an automated parallel synthesis platform was built and utilized for the reductive dehalogenation reactions providing 5-aminotriazoles (5).     

Identification and structural characterization of a transient radical species in the uricase reaction mechanism

Uricase catalyzes the oxidation of urate to form allantoin, carbon dioxide and hydrogen peroxide. In this article, we demonstrate for the first time the presence of a radical intermediate involved in the reaction mechanism. Such radical species was entrapped using 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide as spin trap and the relative adduct was detected by electron paramagnetic resonance (EPR) technique. A structure of such radical (5-hydroperoxy isourate) is proposed, through chemical results and density functional theory calculations of the EPR coupling constants.     

Homogeneous catalysis on the gas-phase dehydration reaction of tertiary alcohols by hydrogen bromide. Density functional theory calculation

The gas-phase thermal dehydration mechanism of tert-butanol, 2-methyl-2-butanol, 2-methyl-2-pentanol and 2,3-dimethyl-2-butanol by homogeneous catalysis of hydrogen bromide was examined by density functional theory calculations with the hybrid functionals: M062X, CAMB3LYP and WB97XD. Reasonable agreements were found between theoretical and experimental enthalpy values at the WB97XD/6-311++G(d,p) level. The dehydration mechanism of tert-butanol with and without catalysis was evaluated in order to examine the catalyst effect on the mechanism. The elimination reaction without catalysis involves a four-membered transition state (TS), while the reaction with catalysis involves a six-membered TS. The mechanism without catalysis has enthalpy activation over 150 kJ mol^–1 greater than the catalysed reaction. In all these reactions, the elongation of the C–O bond is significant in the TS. The un-catalysed reaction is controlled by breaking of C–O bond, and it was found to be more synchronous (Sy ≈ 0.91) than the hydrogen bromide catalysed reactions (Sy ≈ 0.75–0.78); the latter reactions are dominated by the three reaction coordinates associated with water formation. No significant effect on the enthalpies of activation was observed when the size of the alkyl chain was increased.     

Ultrasonic-assisted synthesis of chrysin derivatives linked with 1,2,3-triazoles by 1,3-dipolar cycloaddition reaction

The 1,3-dipolar cycloaddition reaction between 7-(3-azidopropoxy)-5-hydroxyflavone and phenylacetylene was carried out to investigate the synthesis of 7-(3-(4-phenyl-1,2,3-triazol-1-yl)propoxy)- 5-hydroxyflavone in presence of ultrasound (sono-synthesis) and absence of ultrasound (conventional method) under relatively optimized solvent and catalyst conditions. The reaction rate was notably accelerated with the help of ultrasound irradiation. An experiment was especially carried out for investigating the acceleration mechanism of ultrasound on the cycloaddition. A novel series of chrysin derivatives linked with 1,2,3-triazoles were obtained by the copper(I)-catalyzed 1,3-dipolar Huisgen cycloaddition reaction using t-BuOH/H(2)O (1:1 v/v) as reaction solvents and CuSO(4)·5H(2)O/sodium ascorbate as the catalyst at room temperature in the presence of ultrasound irradiation. Their structures are elucidated by NMR, ESI MS, IR and Elemental analysis.     

Ultrasound assisted synthesis of some new 1,3,4-thiadiazole and bi(1,3,4-thiadiazole) derivatives incorporating pyrazolone moiety

Novel substituted 1,3,4-thiadiazole and bi(1,3,4-thiadiazole) were synthesized from reaction of 1-methyl-5-oxo-3-phenyl-2-pyrazolin-4-thiocarbox-anilide with a series of different hydrazonyl halides or N,N'-diphenyl-oxalodihydrazonoyl dichloride. The reactions were carried out under both conventional and ultrasonic irradiation conditions. In general, improvement in rates and yields were observed when reactions were carried out under sonication compared with classical condition. Structures of the products were established on analytical and spectral data.     

手性薄荷酮腙与一氧化氮反应产物的NMR谱研究

在温和条件下手性薄荷酮腙(1)与NO在痕量O₂存在下发生偶氮-硝化反应,高选择性的生成α-硝基偶氮化合物. 通过DEPT谱、1D NOE差谱和¹H- ¹H COSY,HSQC等2D NMR技术对目标化合物2（2,4-二硝基苯基-1-硝基-(2-异丙基-5-甲基)环己基-二氮烯）的¹H,¹³C NMR 谱的信号进行了全归属和较详细的解析,确定了目标化合物2的结构.     

Efficient library synthesis of imidazoles using a multicomponent reaction and microwave irradiation

Optimization of Radziszewski's four-component reaction employing a microwave-assisted protocol, led to a small library of 48 imidazoles with a success rate of 65% (conversion > 45%). All three diversity points of the four-component reaction were varied. Aromatic and aliphatic inputs were successfully implemented and mono-, di-, tri- and tetrasubstituted imidazoles with various substitution patterns were synthesized. Furthermore, unsymmetrical diketones could successfully be used which improved the intrinsic diversity of the method significantly. If the unsymmetrical diketone 1,2-phenylpropanedione (R¹ and R²) was used two regioisomers were formed. Depending on the type of amine (R⁴) and aldehyde (R³) applied, regioselectivity was modest to good. Based on these results, a reaction mechanism is proposed.     

Steric effects on the mechanism of reaction of nucleophilic substitution of β‐substituted alkoxyvinyl trifluoromethyl ketones with four secondary amines

The kinetics of the reaction of β‐substituted β‐alkoxyvinyl trifluoromethyl ketones R¹O‐CR²?CH‐COCF₃ ( 1a – e ) [( 1a ), R¹?C₂H₅, R²?H; ( 1b ), R¹?R²?CH₃; ( 1c ), R¹?C₂H₅, R²?C₆H₅; ( 1d ), R¹?C₂H₅, R²?V^?pNO₂C₆H₄; ( 1e ), R¹?C₂H₅, R²?C(CH₃)₃] with four aliphatic amines ( 2a – d ) [( 2a ), (C₂H₅)₂NH; ( 2b ), (i‐C₃H₇)₂NH; ( 2c ), (CH₂)₅NH; ( 2d ), O(CH₂CH₂)₂NH] was studied in two aprotic solvents, hexane and acetonitrile. The least reactive stereoisomeric form of ( 1a – d ) was the most populated ( E‐s‐Z‐o‐Z ) form, whereas in ( 1e ), the more reactive form ( Z‐s‐Z‐o‐Z ) dominated. The reactions studied proceeded via common transition state formation whose decomposition occurred by ‘uncatalyzed’ and/or ‘catalyzed’ route. Shielding of the reaction centre by bulky β‐substituents lowered abruptly both k′ (‘uncatalyzed’ rate constant) and k″ (‘catalyzed’ rate constant) of this reaction. Bulky amines reduced k″ to a greater extent than k′ as a result of an additional steric retardation to the approach of the bulky amine to its ammonium ion in the transition state. An increase in the electron‐withdrawing ability of the β‐substituent increased ‘uncatalyzed’ k′ due to the acceleration of the initial nucleophile attack (k₁) and ‘uncatalyzed’ decomposition of transition state (k₂) via promoting electrophilic assistance (through transition state 8 ). The amine basicity determined the route of the reaction: the higher amine basicity, the higher k₃/k₂ ratio (a measure of the ‘catalyzed’ route contribution as compared to the ‘uncatalyzed’ process) was. ‘Uncatalyzed’ route predominated for all reactions; however in polar acetonitrile the contribution of the ‘catalyzed’ route was significant for amines with high pK_a and small bulk. Copyright © 2007 John Wiley & Sons, Ltd.     

Design and Synthesis of Highly Photostable Yellow–Green Emitting 1,8-Naphthalimides as Fluorescent Sensors for Metal Cations and Protons

Two highly photostable yellow–green emitting 1,8-naphthalimides 5 and 6, containing both N-linked hindered amine moiety and a secondary or tertiary cation receptor, were synthesized for the first time. Novel compounds were configured as “fluorophore–spacer–receptor” systems based on photoinduced electron transfer. Photophysical characteristics of the dyes were investigated in DMF and water/DMF (4:1, v/v) solution. The ability of the new compounds to detect cations was evaluated by the changes in their fluorescence intensity in the presence of metal ions (Cu²⁺, Pb²⁺, Zn²⁺, Ni²⁺, Co²⁺) and protons. The presence of metal ions and protons was found to disallow a photoinduced electron transfer leading to an enhancement in the dye fluorescence intensity. Compound 5, containing secondary amine receptor, displayed a good sensor activity towards metal ions and protons. However the sensor activity of dye 6, containing a tertiary amine receptor and a shorter hydrocarbon spacer, was substantially higher. The results obtained indicate the potential of the novel compounds as highly photostable and efficient “off–on” pH switchers and fluorescent detectors for metal ions with pronounced selectivity towards Cu²⁺ ions.     

噻吩甲酰基吡唑啉酮缩β-丙氨酸配合物的合成、表征及极谱行为

在非水溶剂中 ,β 丙氨酸与 1 苯基 3 甲基 4 (2 噻吩甲酰基 )吡唑啉酮 5反应合成新型酰基吡唑啉酮席夫碱化合物 1 苯基 3 甲基 4 (2 噻吩甲酰基 )吡唑啉酮 5缩 β 丙氨酸 (HL) .通过回流席夫碱和金属硝酸盐合成了UO2 (Ⅱ )、Cu(Ⅱ )、Co(Ⅱ )和Fe(Ⅱ )金属配合物 .在乙酸 乙酸钠 (pH =4 .6 )缓冲溶液 饱和甘汞电极体系中 ,测量电位 - 1.2 4V处 ,测得铜配合物的极谱波 .元素分析及摩尔电导值表明 ,新配合物的组成为 [UO2 L2 ]·H2 O ,[CuL2 ]·2H2 O ,[CoL2 ]·2H2 O和 [FeL2 ]·2H2 O .运用红外光谱、紫外光谱、核磁共振谱、热谱和磁矩对配合物进行了表征 .结果表明 ,配合物的中心离子 (除UO2 2 + 以外 )均为 6配位 .铜配合物的Cu2 + 还原产生峰电流 ,其电极反应转移 1个电子 .