Mercury chloride assisted cyclization toward benzimidazoles by focused microwave irradiation

An efficient, microwave-assisted method for the mercury chloride mediated synthesis of 1,2-disubstituted benzimidazoles has been developed. Biologically interesting benzimidazoles were readily assembled utilizing S_NAr reactions, reduction, and followed with mercury(II) mediated cyclization under microwave irradiation. The desired products were then liberated from the soluble matrix in excellent yield and purity after cleavage.     

无溶剂微波辅助合成醚类化合物的工艺探讨

与传统加热方法相比,通过体系内部分子运动摩擦产热的微波辐射方法可催化化学反应,缩短反应时间,提高转化率和收率.传统的加热方法需要数十小时,甚至几天的反应.     

微波辅助脱除煤中有机硫的机理研究

为阐明微波场联合过氧乙酸(PAA)脱除煤中有机硫的机理,选取山西临汾(LF)、宁夏宁东(ND)、山西灵石(LS)和河南洛阳(LY)脱矿物质煤及三种含硫模型化合物苄硫醇(Benzyl mercaptan, BM)、苯并(b)噻吩(Benzo (b) thiophene, BT)和二苯基亚砜(Diphenyl sulfoxide, DS)作为研究对象。微波功率为100 W,并联合PAA,辐照1-5 min,通过X射线光电子能谱仪(X-ray photoelectron spectroscopy, XPS)分析固相中硫形态的变化;通过离子色谱仪(Ion chromatography, IC)分析脱硫后液相中SO_4~(2-)的浓度;通过气相色谱-质谱联用仪(Gas chromatography/mass spectrometry, GC/MS)分析萃取物中硫形态的变化。结果表明,有机硫化物硫的含量高,脱硫率大,LY和LS最大脱硫率分别高达55.06%和45.78%,ND和LF最大脱硫率分别为31.24%和28.21%,煤中的硫醇比噻吩和亚砜更易脱除,且脱硫过程中硫形态逐渐向高价态转化,含硫键在微波场中断裂,最终可被PAA氧化为SO_4~(2-)。     

An efficient transformation of cellulose into cellulose carbamates assisted by microwave irradiation

Cellulose carbamates (CCs) were microwave-assisted synthesized from the native cellulose and urea under solvent-free and catalyst-free conditions. Types of raw materials, the effects of the reaction condition on the nitrogen content of CCs were investigated. CCs were characterized with infrared spectroscopy (FT-IR), ¹³C NMR spectrometry, X-ray diffraction, scanning electron microscopy and thermogravimetry. The results indicated that various source of native celluloses such as cotton linter, reed, bagasse and wood pulps with different degree of polymerization could be successfully converted to CCs by the efficient and environmentally friendly procedure. The nitrogen content of CCs increased with an increase of the urea content and the mass of the mixtures, as well as the pulsed times of microwave irradiation. CCs retained the cellulose I crystalline form of the native cellulose and the degree of crystallinity decreased with the incorporation of carbamates. This work provided a novel pathway for the preparation of cellulose carbamate, which is expected to be useful for the CarbaCell process.     

Unexpected synthesis of aziridines under Cu(I) catalyzed Kinugasa conditions assisted by microwave irradiation

Cu(I)-catalyzed 1,3-dipolar cycloaddition between chiral nitrone and terminal alkynes under microwave irradiation afforded a series of enantiopure aziridines with the creation of two contiguous stereogenic centers.     

A straightforward synthesis of pyrimido[4,5-b]quinoline derivatives assisted by microwave irradiation

Several pyrimido[4,5-b]quinolines, flavin analogues, have been prepared by assisted microwave intramolecular cyclization of N⁴-substituted-2,4-diamino-6-chloropyrimidine-5-carbaldehydes. The reaction takes place with hydrolysis of amino-group and chlorine. Particularly valuable features of this method included the broader substrate scope and operational simplicity as well as increased safety for small-scale high-speed synthesis.     

Exploring SmBr2-, SmI2-, and YbI2-mediated reactions assisted by microwave irradiation

The use of microwave heating in lanthanide(II) halide (LnX2 = SmBr2, SmI2, and YbI2) mediated reduction and coupling reactions has been investigated for a variety of functional groups including alpha,beta-unsaturated esters, aldehydes, ketones, imines, and alkyl halides. Good to quantitative transformations were obtained within a few minutes without the addition of any co-solvents, such as hexamethyl phosphoramide (HMPA). The redox potential of YbI2 in tetrahydrofuran (THF) has been determined as -1.02+/-0.05 V (versus Ag/AgNO3) by cyclic voltammetry. A large selectivity difference in various reactions was observed depending on the redox potential of the LnX2 reagent. The more powerful reductant, SmBr2, afforded mainly pinacol-coupling products of ketones whereas the weaker reductant YbI2 afforded mainly reduction products. The results indicate that the reducing power of LnX2 has a large impact on not only the pinacol coupling/reduction product ratio of ketones but also on other substrates in which there are competing coupling and reduction reactions. The use of in situ generated LnX2 has also been explored and proven useful in many of these reactions.     

Facile and efficient synthesis of acridinediones from primary amino alcohols via three-component condensation reactions assisted by microwave irradiation

Microwave irradiation of three component reaction of dimedone, appropriate aromatic aldehydes and amino alcohols in a stoichiometrical ratio 2:1:1 for few minutes afforded the formation of a stable fused three membered ring of the corresponding 3,6,6-tetramethyl-2,3,4,5,6,7,8,9,10-decahydroacridine-1,8-dione derivatives in an excellent yield (80–91%). The structure of all products has been characterized by X-ray crystal structural analyses, ¹³C NMR, ¹H NMR, IR and mass spectrum analyses.     

Determination of Pt from coke samples by ICP-MS after microwave assisted digestion and microwave assisted cloud point extraction

Platinum in coke samples was determined by inductively coupled plasma mass spectrometry (ICP-MS) after microwave-assisted sample digestion and temperature controlled microwave assisted cloud point extraction (MW-CPE). Interferences due to hafnium (¹⁷⁹Hf¹⁶O) were successfully eliminated using MW-CPE with 2-MBT prior to the determination of platinum by ICP-MS. The validity of the method was studied by spike recovery tests and by analyzing certified reference material (BCR-723 street dust). The results obtained for platinum in the BCR-723 were generally in good agreement with the certified values. Furthermore, the preliminary platinum results obtained for coke sample by ICP-MS after MW-CPE were compared to those obtained by a reference method (NiS-Fire Assay preconcentration/Te coprecipitation and ICP-MS determination).     

Traceless synthesis of hydantoin by focused microwave irradiation

An efficient, microwave-assisted method for the liquid-phase combinatorial synthesis of 1,3-disubstituted hydantoin has been developed. Chloroacetyl chloride was directly anchored to HO-PEG-OH and subsequently reacted with various primary amines in a microwave cavity. The PEG bound secondary amine coupled with isocyanates and concomitant cyclization-cleavage step occurred in mild basic conditions by microwave flash heating. The desired products were then liberated from the soluble matrix in modest yield and high purity.     

二茂铁基1,4-Dihydropyridine类似物的合成

1 ,4 二氢吡啶衍生物是一类有着多种生物活性的化合物 ,具有扩张血管、抗高血压、抗动脉粥状硬化、抗肿瘤、抗糖尿病、抗衰老等作用 ,是七十年代以来相继开发的一类新型高效的钙离子拮抗剂 ,临床上用于治疗高血压、心绞痛、充血性心衰和动脉粥状硬化等心脑血管疾病及肠胃疾病、雷诺氏病 ,还可以作为辅佐药物治疗肺动脉高压和癫痫病[1 ] 。近年来 ,二茂铁衍生物在生物学、医学等方面得到了广泛的研究和应用 ,主要是由于它们的结构和性质有自身的特殊性 :二茂铁有卓越的芳香性 ,易发生取代反应 ,易进行修饰 ,并且在许多介质中有较好的稳定性 ;…     

Combinatorial synthesis of biheterocyclic benzimidazoles by microwave irradiation

Liquid phasel synthesis of biheterocyclic benzimidazoles by controlled microwave irradiation was investigated. Polymer immobilized o-phenylenediamines was synthesized under microwave irradiation. The resulting PEG bound diamines was N-acylated with 4-fluoro-3-nitrobenzoic acid selectively in primary aromatic amino moiety. Nucleophilic aromatic substitution of amide was performed with various amines then cyclized to form the first benzimidazole scaffold in acidic condition. Successive reduction, cyclization with isothiocyanates yielded 5-(benzimidazol-2-yl)benzimidazoles. The desired products were released from the polymer support to afford the tri-substituted bis-benzimidazoles in good yields and purity.     

Liquid phase synthesis of chiral quinoxalinones by microwave irradiation

Single mode microwave-assisted combinatorial synthesis of biologically interesting quinoxalinones is described. Chiral libraries of quinoxalinone were readily assembled utilizing S_NAr reactions, reduction and followed with concomitant cyclization under microwave irradiation. Enantiomeric 1,2,3,4-tetrahydroquinoxalinones were isolated in excellent yield and purity after cleavage.     

Parallel synthesis of amino bis-benzimidazoles by multistep microwave irradiation

A multistep liquid phase synthesis of specifically functionalized bis-benzimidazoles is presented by the application of single-mode microwave irradiation technique. The sustained solubilizing power and stability of the PEG-ester derived from the commercially available 4-fluoro-3-nitrobenzoic acid has been successfully carried through 10 steps involving ipso-S_NAr reaction, neutral reduction and acid cyclization. All the steps in this synthetic sequence were assisted by microwave (MW) irradiation. The polymer support was cleaved to release the final head to tail bisbenzimidazoles in an efficient process.     

Traceless polymer-supported divergent synthesis of quinoxalinones by microwave irradiation

A novel protocol for rapid assemble of quinoxalinones framework has been demonstrated. This method incorporated with soluble polymer support provides a convenient approach for diversification of heterocyclic compounds and for easy purification via facile precipitation from reaction matrix. The key transformation of this study involves in situ reduction of aromatic nitro compound, tandem lactamization concomitant with traceless cleavage of the polymer support under microwave irradiation in a one-pot fashion. Moreover, forward synthetic routes were introduced to maximize complexity of the master intermediate on which further chemical elaboration was applied. The strategy is envisaged to apply for establishment of drug-like small-molecule libraries for high-throughput screening.     

Fast synthesis of temperature-sensitive PNIPAAm hydrogels by microwave irradiation

A novel method, microwave irradiation synthesis, is proposed for the preparation of thermo-sensitive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels. The PNIPAAm hydrogels were separately synthesized by using microwave irradiation method and water-bath heating method. Chemical groups, lower critical solution temperature (LCST) and surface morphology of these PNIPAAm hydrogels were characterized by FT-IR, DSC and SEM. Swelling ratios of the gels were measured gravimetrically in the temperature range from 10.0 to 60.0 °C. Results showed that (1) the use of microwave irradiation can greatly shorten the reaction time required for PNIPAAm hydrogel synthesis from several hours to several minutes in comparison with water-bath heating method, and obviously improve the yields of the PNIPAAm gels, which were up to 99% after a short reaction time; (2) SEM micrographs and textural measurement revealed that the gels synthesized using microwave irradiation had more porous structure, and their average pore sizes and specific surface areas were larger than those of the gels synthesized using water-bath heating method; and (3) the PNIPAAm hydrogels synthesized using microwave irradiation had much higher swelling ratios at 10.0 °C below the LCST, and had lower swelling ratio at 60.0 °C above the LCST compared to the hydrogels synthesized by water-bath method.     

Unique microstructure of glass-metal composites obtained by microwave assisted heat-treatments

The present study deals with the computer-aided simulation of the microwave heating of metal/glass composites in single mode applicator and the rapid densification of borosilicate glass matrix composites containing molybdenum particle inclusions. The selective and penetrating microwave heating led to a layered porous structure of the samples. They consisted of a highly porous core containing spherical pores and a relatively dense outer shell. Pores in the central region were formed in the molten glass phase due to gas evolution and entrapment. The outer region of the sample remained at lower temperature and it sintered by viscous flow with minimal distortion. This revised version was published online in July 2006 with corrections to the Cover Date.