Synthesis of aminouracil-tethered tri-substituted methanes in water by iodine-catalyzed multicomponent reactions

Molecular Diversity - An efficient, mild and environmentally benign protocol has been developed for the synthesis of aminouracil-tethered tri-substituted methane derivatives. The three-component...     

Base catalyzed multicomponent synthesis of spiroheterocycles with fused heterosystems

Structurally diverse spiroheterocycles incorporating medicinally privileged heterosystems have been synthesized by a simple and convenient synthesis involving triethylamine catalyzed multicomponent domino reaction of 2-aminobenzothiazoles with isatin and cyclic 1,3-diketones.     

A novel protocol for catalyst-free synthesis of fused six-member rings to triazole and pyrazole

Molecular Diversity - Herein, an effectual, quick and novel method is described for the synthesis of new triazolo[1,5-a]pyrimidine, triazolo[5,1-b][1,3] thiazine and pyrazolo[1,5-a]pyrimidine...     

Synthesis of isoindolin-1-one derivatives via multicomponent reactions of methyl 2-formylbenzoate and intramolecular amidation

Four series of heterocyclic compounds were obtained using Ugi-type multicomponent reactions (MCRs) with methyl 2-formylbenzoate as one of the starting materials. A facile and efficient one-pot procedure was suitable for all the MCRs under acidic conditions. This process provided access to four series of complex and potentially biologically active scaffolds.     

Recent progress of isocyanide-based multicomponent reactions in Iran

The aim of this review is to provide an overview of the contributions and recent advances made by Iranian scientists in the field of isocyanide-based reactions between 1999 and 2009. With over 100 publications during this period, Iranians are responsible for approximately 10% of all publications in the world involving isocyanide-based multicomponent reactions (IMCRs). Some important aspects of these IMCRs include the execution of reactions in green reaction mediums like water or ethanol, high atom economies, mild reaction conditions, high yields, and catalyst-free processes. On the other hand, in most of these reactions, new classes of heterocyclic compounds with potential biological and medicinal activities have been reported.     

Synthesis of tetracyclic pyrido-fused dibenzodiazepines via a catalyst-free cascade reaction

Molecular Diversity - An efficient, eco-friendly protocol has been described for the chemoselective synthesis of tetracyclic pyrido-fused dibenzodiazepines derivatives via catalyst-free,...     

Catalysis by basic carbons: Preparation of dihydropyridines

The condensation of benzaldehyde and different substituted benzaldehydes, such as 2-nitrobenzaldehyde, 3-nitrobenzaldehyde, and 2,4-dichlorobenzaldehyde, with ethyl cyanoacetate was carried out using two alkaline carbons (Na-Norit and Cs-Norit) as catalysts in the absence of solvent. The reaction products are precursors in the production of 1,4-dihydropyridine derivatives, which have expanding practical applications as pharmaceuticals in the line of calcium channel blockers. High values of activity and selectivity were obtained. The most active carbon (Cs-Norit), which contains basic sites with pK_b = 11.2, is more active than pyridine, and less than piperidine. The selectivity to the desired condensation product when using these activated carbons is, at least, as high as in the case of the homogeneous catalyst. This “green” and “clean” method (alkaline doped carbon catalyst in the absence of solvent) can be extended to the preparation of other intermediates with medical applications.     

High pressure: A promising tool for multicomponent reactions

In this paper the application of high pressure in multicomponent reactions is discussed. Using high pressure the scope of certain multicomponent reactions can be increased. Reactions are described that can only be performed in a multicomponent fashion when high pressure catalysis is applied. An overview of high pressure catalysed multicomponent reactions is presented with special attention to the domino [4 + 2]/[3 + 2] cycloaddition reaction.     

Macrocycles rapidly produced by multiple multicomponent reactions including bifunctional building blocks (MiBs)

Naturally occurring macrocycles often exhibit remarkable biological activities and, therefore, constitute an attractive starting point for diversity-oriented synthesis for lead discovery in drug development. Multicomponent reactions have been used for the introduction of chemical diversity in strategies towards macrocycle libraries, mostly by combinational synthesis of a linear precursor combined with a subsequent macrocyclization reaction. The Ugi reaction in particular may be used for the macrocyclization itself as well, and a library of natural product-like macrocycles can be constructed in a single step from simple precursors. The efficiency and versatility of both strategies is immense and is exemplarily illustrated by the construction of small libraries of cyclopeptide alkaloid derivatives and biaryl ether macrocycles. The syntheses of the latter compound group are examples of multiple multicomponent macrocyclizations including bifunctional building blocks (M³iB³ or MiB), of which the Ugi-MiBs and their variations are discussed in more detail.     

4-Hydroxy-2-quinolones: syntheses,reactions and fused heterocycles

Molecular Diversity - The interesting pharmaceutical and biological activities of 4-hydroxy-2-quinolones make them valuable in drug research and development. Hence, many publications have recently...     

Greener organic synthetic methods: Sonochemistry and heterogeneous catalysis promoted multicomponent reactions

Ultrasound is an essential technique to improve organic synthesis from the point of view of green chemistry, as it can promote better yields and selectivities, in addition to shorter reaction times when compared to the conventional methods. Heterogeneous catalysis is another pillar of sustainable chemistry being the recycling and reuse of the catalysts one of its great advantage. In the other hand, multicomponent reactions provide the synthesis of structurally diverse compounds, in a one-pot fashion, without isolation and purification of intermediates. Thus, the combination of these protocols has proved to be a powerful tool to obtain biologically active organic compounds with lower costs, time and energy consumption. Herein, we provide a comprehensive overview of advances on methods of organic synthesis that have been reported over the past ten years with focus on ultrasound-assisted multicomponent reactions under heterogeneous catalysis. In particular, we present pharmacologically important N- and O-heterocyclic compounds, considering their synthetic methods using green solvents, and catalyst recycling.     

Synthesis of photocatalytic active fibrous titania by the solvothermal reactions

Abstract

Fibrous titania was synthesized by the solvothermal reactions of H₁Ti₄O₉ nH₂in different media. H₂Ti₄O₉·nH₂O transformed in steps to H₂Ti₈O₁₇, monoclinic TiO_z, anatase and rutile. The phase transformation temperature and microstructure of the products changed significantly depending on the heating environment. The critical temperature at which anatase appeared in liquid media was much lower than that in air. The titania fibers consisted of nanocrystals of TiO₂. The crystallite size and crystallinity of titania decreased with decreasing the dielectric constant of the reaction medium. Consequently, the photocatalytic activity of titania changed with heat treatment media in the following sequence: ethanol, methanol > water > air, i.e., fibrous titania possessing excellent photocatalytic activity could be obtained by the solvothermal reactions using alcohol such as methanol and ethanol. Titania powders crystallized by the solvothermal reaction in methanol also possessed excellent thermal stability.     

Facile and efficient synthesis of functionalized iminothiopyran and isothiochromen via one-pot multicomponent reactions

An efficient synthesis of 6H-6-iminothiopyran-2,3-dicarboxylate and 1H-isothiochromene-3,4-dicarboxylate derivatives via one-pot reactions between acetylenic esters, aryl isothiocyanates and enaminones in dichloromethane at room temperature is described. The mild reaction condition, high yields and the new products are advantages of our method.     

Synthesis of heavy and superheavy elements by reactions of massive nuclei

By comparing theoretical and experimental excitation functions of evaporation residues resulting from the same compound nucleus or heavy and superheavy nuclei, it is possible to understand the effect of the entrance channel and the shell structure of reacting nuclei on the fusion mechanism. The competition of complete fusion with the quasifission process is strongly related to the intrinsic fusion barrier B _fus ^* and the quasifission barrier B _qf as well as the size of the well in the nucleus-nucleus potential. In our calculations of the excitation functions for capture, fusion, and evaporation residues, we use the relevant variables such as mass asymmetry of nuclei in the entrance channel, potential energy surface, driving potential, spin distribution, and surviving probability of compound nucleus that are responsible for the mechanism of the fusion-fission process. As a result, we obtain a beam energy window for the capture of the nuclei before the system fuses and the Γ_n/Γ_f ratio at each step along the deexcitation cascade of the compound nucleus. Calculations performed in the framework of the model taking into account the nuclear shell effect and shape of colliding nuclei allow us to reach useful conclusions about the mechanism of the fusion-fission process and the production of the evaporation residues. We analyze the ⁴⁰Ar + ¹⁷⁶Hf, ⁸⁶Kr + ¹³⁰Xe, and ¹²⁴Sn + ⁹²Zr reactions leading to ²¹⁶Th*; the ³²S + ¹⁸²W and ⁶⁰Ni + ¹⁵⁴Sm reactions leading to ²¹⁴Th*; the ⁴⁸Ca + ²⁴⁸Cm reaction leading to the ²⁹⁶116 compound nucleus; and the ⁴⁸Ca + ²⁴⁹Cf reaction leading to the ²⁹⁷118 compound nucleus.     

Optical emission from disordered multi-branched ZnO nanorods formed by catalyst-free growth

We have demonstrated catalyst-free fabrication of multi-branched ZnO nanorods and their interesting optical properties. Under Xe lamp excitation (325 nm), it is found that the ethanol rinsing leads to an obviously enhanced ultraviolet emission at room temperature. Moreover, temperature-dependent emission spectra exhibit an anomalous temperature dependence of the ultraviolet emission intensity. This has been analyzed in terms of the competition between the radiative and nonradiative hopping processes using a model developed for disordered porous semiconductors. With femtosecond pulse excitation (640 nm), two-photon-induced photoluminescence is observed, which is confirmed by the quadratic dependence of the emission intensity on the excitation pulse energy.     

Position-controlled and catalyst-free growth of ZnO nanocrystals by nanoparticle-assisted pulsed laser deposition

We have synthesized ZnO nanocrystals, such as nanowires, nanorods, and nanosheets, using a nanoparticle-assisted pulsed laser deposition (NAPLD) method. Recently, we achieved position-controlled growth of the ZnO nanocrystals by means of a ZnO buffer layer and laser irradiation without any catalyst. The periodic structure was formed on the ZnO buffer layer by multi-beam interference patterning, and then vertically aligned ZnO nanowalls, corresponding to the patterning, were grown on the buffer layer. It was found that the periodic ZnO nanowalls grew along the c-axis direction by X-ray diffraction measurement. The well-aligned ZnO nanowalls are expected to be utilized as building blocks for field emitters and UV LEDs. The proposed technique can be used as one of the effective methods to control the growth position of the ZnO nanocrystals because various structures can be easily fabricated by a laser writing and a spatial light modulator.     

Influence of heterogeneous chemical reactions on the slip velocity of an inhomogeneous multicomponent gaseous mixture

In constructing a theory of thermal diffusiophoresis of volatile aerosol particles it is necessary to have boundary conditions for the tangential velocity component which allow for the presence of heterogeneous chemical reactions. Conditions of this sort have been obtained by a number of authors [R. N. Gupta et al., Technical Papers, AIAA 22nd Aerospace Science Meeting, AIAA 19th Thermophysics Conference, New York (1985), pp. 465–490; D. V. Kul’ginov, Tech. Phys. 63, 940 (1993); A. V. Bogdanov et al., Preprint No. 1051, Fiz-Tekh. Inst. Akad. Nauk. SSSR, Leningrad (1986)]. The results of Gupta et al. are in the form of analytical expressions, but their computations actually used Maxwell’s method, which is of low accuracy. Kul’ginov et al. and Bogdanov et al. used the method of matched asymptotic expansions, which did not permit them to get simple analytical expressions. In the present paper the slip velocity is calculated by the Loyalka method. Analytical expressions are obtained for the slip coefficients, and the results of numerical calculations are presented. It is shown that in the presence of concentration gradients of the components of the gaseous mixture along the surface of an aerosol particle, the slip velocity can acquire new terms due to the change in the sticking coefficient along the catalytic surface. Expressions in final form are given for these terms. Zh. Tekh. Fiz. 67, 29–33 (May 1997)