Microwave Promoted Rapid Dehydration of Aldoximes to Nitriles on a Solid Support †

Aldoximes undergo rapid dehydration with H₂SO₄/ SiO₂ solid support, under microwave irradiation in dry media to afford nitriles in high yields.

     

Mild,Efficient, and Rapid Dehydration of Aldoximes to Nitriles Mediated by Phthalic Anhydride Under Microwave Irradiation

Summary.  Aldoximes can be efficiently and rapidly dehydrated to nitriles by treatment with phthalic anhydride under microwave irradiation. Received April 18, 2001. Accepted (revised) June 7, 2001     

Micowave assisted synthesis of benzo‐substituted macrocyclic diamides and their corresponding macrocyclic dithiodiamides

A synthesis of a series of macrocyclic diamides 3 in good yields by reacting the corresponding bis phenols 4 with the appropriate dihalo alkanes 6 either in solvent or in dry media under microwave irradiation. Thiation of 3 with P₂S₅ or Lawesson's reagent in solvent free conditions under microwave irradiation is also described.     

Microwave Induced Bismuth Trichloride Catalysed Beckmann Rearrangement of Oximes

A new and efficient method for the rearrangement of oximes 1 has been achieved by a simple reaction of a ketoximes with bismuth trichloride under microwave irradiation in the solid state.     

MICROWAVE-ASSISTED RAPID DEHYDRATION OF ALDOXIMES TO NITRILES ON A SOLID SUPPORT

p-toluenesulfonyl chloride has been proved out to be an efficient reagent for conversion of aldoximes to the corresponding nitriles under microwave irradiation. Extending the procedure to ketoximes, a 20–40% yield of Beckmann rearranged product was obtained.     

Selective introduction of a fluorine atom into carbohydrates and a nucleoside by ring-opening fluorination reaction of epoxides

Ring-opening fluorination reactions of epoxides using tetrabutylammonium bifluoride (TBABF)-KHF₂, or Et₃N-3HF under microwave irradiation were applied for the introduction of a fluorine atom into the carbohydrate molecules. When TBABF-KHF₂ was used as the fluorination reagent, a fluorine atom was introduced regioselectively and various functional groups can tolerate the conditions. When Et₃N-3HF was used under microwave irradiation, the reaction time could be remarkably shortened compared with the conventional oil-bath heating.     

Selectivity under microwave irradiation. Benzylation of 2-pyridone: an experimental and theoretical study

The reaction of 2-pyridone with benzyl bromide in the absence of base and under solvent-free conditions has been studied experimentally and by computational methods. This reaction was one of the first reported examples in which modification of selectivity under microwave irradiation was observed. C- and/or N-alkylations were obtained depending on the benzyl halide and the heating system. N-Alkylation through mechanism A (S_N2 mechanism) is kinetically favoured while C-alkylation through an S_N1-type mechanism is thermodynamically favoured and is observed under microwave irradiation. Two S_N1-type mechanisms (mechanisms B and C) have been calculated, mechanism C being a kind of S_Ni. The influence of the pyridone/benzyl bromide ratio was studied. A second molecule of pyridone stabilizes the transition state and assists the leaving of the bromide ion. The occurrence of C-alkylation under microwave irradiation is explained by the predominance of the thermodynamic control in these conditions. Under microwave irradiation N-alkylation through an S_N1-type mechanism (mechanism C) can also occur. The dependence of the outcome of N-alkylation on the benzyl bromide ratio has been explained by a shift in the mechanism from S_N2 to S_N1 under microwave irradiation. Computational calculations have shown to be a useful tool for determination of the origin of the selectivity under microwave irradiation.     

Ring Opening of a Fatty Epoxide by Diethylacetamido Malonate in Basic Medium by Phase Transfer Catalysis or Under Microwave Irradiation

A fatty epoxide (tetradecyl-oxirane) is reacted with diethyl acetamidomalonate in basic medium, with or without solvent under solid-liquid phase transfer catalysis with LiCl, or under microwave irradiation on supported reagents (KF/Al₂O₃/LiCl). The main product is a lactone which is formed after epoxide ring opening and subsequent cyclisation. We put here into evidence, for the first time, the conjugated advantages of “dry media” reactions, lithium salt effects and microwave irradiation.     

An efficient catalytic method for the Beckmann rearrangement of ketoximes to amides and aldoximes to nitriles mediated by propylphosphonic anhydride (T3P®)

An efficient method for the Beckmann rearrangement of ketoximes to amides mediated by a catalytic amount (15 mol %) of propylphosphonic anhydride (T3P®) is described. Aldoximes underwent second order Beckmann rearrangement to provide the corresponding nitriles in excellent yields on reacting with T3P (15 mol %) at room temperature. The main advantages of this environmentally friendly protocol include procedural simplicity, and particularly ease of isolation of the products.     

微波作用下的多肽固相缩合反应及动力学研究

分别在微波作用以及传统加热两种方式下, 研究了Fmoc-Val-OH与NH₂-Tyr(t-Bu)-Wang树脂的固相缩合反应及其动力学. 测定了温度变化对反应速率的影响, 并获得了两种方式下的缩合反应的宏观动力学参数: 300 W微波作用下表观缩合反应级数为2.3, 活化能为104.7 kJ/mol; 传统方法中表观反应级数为2.9, 活化能为142.4 kJ/mol. 微波作用将常规条件下的连接率由68%提高到95%, 而所需时间降为常规条件的1/14.     

One‐pot Synthesis of Fused Dipyranocoumarins from Dihydroxycoumarins and Propargyl Chlorides under Microwave Irradiation

Dipetalolactone and 4‐methyldipetalolactone are prepared in excellent yield by a one‐pot tandem propargylation/Claisen rearrangement/cyclization reaction of the corresponding 5,7‐dihydroxycoumarins with 3‐chloro‐3‐methylbut‐1‐yne in the presence of Cs₂CO₃ under microwave irradiation. The analogous reactions of propargyl chloride with esculetins or 5,7‐dihydroxycoumarins led to dipropargyloxy derivatives. The later by treatment with gold nanoparticles supported on TiO₂ or BF₃.Et₂O in N,N‐dimethylformamide (DMF) under microwave irradiation resulted in very good to excellent yield to the corresponding fused dipyranocoumarins. The reactions of esculetins with 3‐chloro‐3‐methylbut‐1‐yne gave mainly exomethylene fused dioxino[g]coumarins.     

圆形片状纳米复合材料Ag/ZnO-ZrO2微波辅助合成与多模式光催化罗丹明B

采用微波辅助结合沉淀法制备了以Zn O为主体的纳米复合材料Ag/Zn O-Zr O_2。通过X射线粉末衍射(XRD)、紫外-可见漫反射吸收光谱(UV-Vis/DRS)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)和N2吸附-脱附等表征手段研究了微波辐射对Ag/Zn O-Zr O_2晶型结构、形貌及表面物理化学性质的影响。结果表明,在200 W微波辐射作用下,该样品晶型结构未发生明显变化,但Ag的衍射峰明显增强,同时,其晶粒尺寸、光吸收性质和表面物理化学性质等方面则发生改变,尤其是样品Ag/Zn O-Zr O_2的形貌呈现了圆形片状结构。分别在紫外和微波辅助条件下对纳米复合材料的光催化性能进行了一系列考察,同时为了进一步评价所合成样品在太阳光作用下的实用价值,又考察了Ag/Zn O-Zr O_2在模拟日光条件下的光催化性能。结果显示,紫外光作用下,纳米复合材料Ag/Zn O-Zr O_2的光催化活性高于市售P25以及未经微波处理的样品,且在微波辅助光催化条件下,其活性有较大程度提高。200 W微波功率下所合成样品Ag/Zn O-Zr O_2在模拟日光作用下显现出较高活性。另外,根据紫外光条件下对光催化活性物种的捕获实验提出了Ag/Zn O-Zr O_2可能的光催化机理。     

Reaction of Hydroquinones with Supported Oxidizing Reagents in Solvent-Free Conditions

Supported MnO₂ or HNO₃ on bentonitic clay cleanly oxidize some hydroquinones under infrared or microwave irradiation to the corresponding quinones with excellent conversion in short reaction times, using an easy and solvent-free approach.     

Pd(II)-catalyzed condensation reaction of ketoximes and dichloromethane using potassium superoxide

Methylene dioximes are formed from ketoximes and CH₂Cl₂ using either KO₂ with a catalytic amount of Pd(II) complex $\text{3}$ or K₂CO₃ with 18-crown-6 catalyst. The reactivity of ketoximes towards CH₂Cl₂ is reversed between these two methods.     

Quinoxalinium Fluorochromate (QxFC): A New and Efficient Reagent for the Oxidation of Alcohols in Solution,Under Solvent-Free Conditions and Microwave Irradiation

The new mild oxidizing agent, quinoxalinium fluorochromate (QxFC), has been easily prepared by reacting quinoxaline with an aqueous solution of CrO ₃ and HF. This reagent is suitable for oxidizing various primary and secondary alcohols to their corresponding carbonyl compounds and anthracene to antraquinone. The reactions were carried out in solution, under solvent-free conditions and microwave irradiation. The results show that the rates of the reactions and the yields are usually highest under microwave irradiation.     

圆形片状纳米复合材料Ag/ZnO-ZrO2微波辅助合成与多模式光催化罗丹明B

采用微波辅助结合沉淀法制备了以ZnO为主体的纳米复合材料Ag/ZnO-ZrO₂。通过X射线粉末衍射(XRD)、紫外-可见漫反射吸收光谱(UV-Vis/DRS)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)和N2吸附-脱附等表征手段研究了微波辐射对Ag/ZnO-ZrO₂晶型结构、形貌及表面物理化学性质的影响。结果表明, 在200 W微波辐射作用下, 该样品晶型结构未发生明显变化, 但Ag的衍射峰明显增强, 同时, 其晶粒尺寸、光吸收性质和表面物理化学性质等方面则发生改变, 尤其是样品Ag/ZnO-ZrO₂的形貌呈现了圆形片状结构。分别在紫外和微波辅助条件下对纳米复合材料的光催化性能进行了一系列考察, 同时为了进一步评价所合成样品在太阳光作用下的实用价值, 又考察了Ag/ZnO-ZrO₂在模拟日光条件下的光催化性能。结果显示, 紫外光作用下, 纳米复合材料Ag/ZnO-ZrO₂的光催化活性高于市售P25以及未经微波处理的样品, 且在微波辅助光催化条件下, 其活性有较大程度提高。200 W微波功率下所合成样品Ag/ZnO-ZrO₂在模拟日光作用下显现出较高活性。另外, 根据紫外光条件下对光催化活性物种的捕获实验提出了Ag/ZnO-ZrO₂可能的光催化机理。     

Application of a dimeric ortho‐palladated complex of tribenzylamine as an efficient catalyst in microwave‐assisted Hiyama coupling reactions

The activity of [Pd{C₆H₄(CH₂N(CH₂Ph)₂)}(μ‐Br)]₂ complex was investigated in cross‐coupling reactions of triethoxy(phenyl)silane with various aryl halides under microwave irradiation. This complex is an efficient and stable catalyst for the synthesis of substituted biphenyls that is non‐sensitive to air and moisture. The combination of dimeric complex as homogenous catalyst, microwave irradiation, DMF as microwave‐active polar solvent and TBAF as microwave‐active additive led to excellent yields in short reaction times. Copyright © 2012 John Wiley & Sons, Ltd.     

Copper-catalyzed cross-coupling of aryl iodides and aryl acetylenes using microwave heating

An efficient copper-catalyzed cross-coupling of aryl iodides with aryl acetylenes under microwave irradiation is described. The reaction proceeds under microwave heating with 10 mol % CuI and 2 equiv Cs₂CO₃ in 43-87% yields.     

Palladium-Catalyzed Synthesis of Symmetrical Biaryls Under Microwave Irradiation and Conventional Heating

The activity of the [Pd{C₆H₄(CH₂N(CH₂Ph)₂)}(µ-Br)]₂ complex was investigated in the synthesis of symmetrical biaryls under both conventional and microwave irradiation conditions, and their results were compared. This complex is efficient, stable, and not sensitive to air or moisture and is a catalyst for the homo-coupling reaction of aryl iodides, bromides, and even chlorides. The products were produced in excellent yields in short reaction times using a catalytic amount of [Pd{C₆H₄(CH₂N(CH₂Ph)₂)(µ-Br)]₂ complex in N-methylpyrolidine (NMP) at 130 °C. In comparison to conventional heating conditions, the reactions under microwave irradiation gave better yields in shorter reaction times.     

Silica-supported perchloric acid and potassium bisulfate as reusable green catalysts for nitration of aromatics under solvent-free microwave conditions

Silica-supported perchloric acid and bisulfate (SiO₂/HClO₄ and SiO₂/KHSO₄) have been developed as reusable green catalysts for nitration of aromatic compounds using NaNO₂ in acetonitrile medium under conventional and solvent-free microwave conditions. The reaction times under microwave irradiation are significantly shorter than conventional method even though the yields obtained in microwave-assisted reactions are comparable with those obtained under reflux conditions.