Publications 2007

2007

Microwave-assisted synthesis of bipyrazolyls and pyrazolyl-substituted pyrimidines

Antonio de la Hoz, Angel Diaz, Jose Elguero, Agustin Jimenez, Andres Moreno, Amparo Ruiz, Ana Sanchez-Migallon. The prepn. of 1,4′-bipyrazolyls and 4-pyrazolylpyrimidines, e.g., I and II (X = O or S), by the reaction of 2-pyrazolyl-3-dimethylamino acrylate and acrylonitrile with double nucleophilic reagents such as hydrazines, urea and guanidine was described.  Reactions were performed under microwave irradn. in 5-60 min.  This could be a useful procedure for the prepn. of valuable compds. with applications in medicinal and coordination chem. – Tetrahedron (2007) vol. 63 (3) pp. 748-753

Diels-Alder Reaction of Triazoles with DMAD Catalyzed by Silica-Bound AlCl3

A Díaz-Ortiz, A De Cózar, P Prieto, A De La Hoz, A Moreno. Synfacts (2007) vol. 2007 (02) pp. 218

Reversible Microwave-Assisted Cycloaddition of Aziridines to Carbon Nanotubes

Fulvio Brunetti, M Herrero, Juan Muñoz, Silvia Giordani, Angel Díaz-Ortiz, Salvatore Filippone, Giorgio Ruaro, Moreno Meneghetti, Maurizio Prato, Ester Vázquez. We report a new approach that uses microwaves to rapidly functionalize carbon nanotubes by using 1,3-dipolar cycloaddition of aziridines, well-known precursors to azomethine ylides, in solvent-free conditions. The efficiency of our microwave-mediated protocol is confirmed by comparison to a similar protocol in classical conditions for the azomethine ylides in DMF. Under these latter conditions, the reaction proceeds in 5 days (against 1 h under microwave irradiation), and the functionalization degree is much lower, as confirmed by thermogravimetric analysis and Raman spectroscopy. With our procedure, we easily scale-up the reaction up to 250 mg of functionalized MWNT in 1 h. We also provide an indirect proof of the covalent sidewall functionalization of the tubes. – Journal of the American Chemical Society (2007) vol. 129 (47) pp. 14580-14581

M. V. Gomez, D. N. Reinhoudt, A. H. Velders, in Proceedings of Micro Total Analysis Systems, Vol. 1(Eds.: J.-L. Viovy, P. Tabeling, S. Descroix, L. Malaquin), Paris, 2007, pp. 506

Primary product distribution from the Cl-atom initiated atmospheric degradation of furan: Environmental implications

Florentina Villanueva, Ian Barnes, Esperanza Monedero, Sagrario Salgado, Mª Gómez, Pilar Martin. Furan is an aromatic hydrocarbon present in both urban and rural atmospheres, which is emitted mainly by biomass burning and the combustion of fossil fuel. Reaction of furan and Cl atoms may be important in areas where chlorine atom concentrations are potentially high such as marine and coastal regions or continental atmospheres where industrial activity emits molecular chlorine or photo-labile Cl-containing compounds. To assess the importance of this reaction and to investigate whether any unique chlorine-containing product is formed the products of the reaction of Cl atoms with furan have been determined under atmospheric conditions. For the study two different sampling/detection methods have been used: (1) Solid-Phase MicroExtraction, with subsequent analysis by thermal desorption, and gas chromatography with mass spectrometry or flame ionization detection (SPME/GC-MS/FID), and 2-“in situ” with long path fourier transform infrared spectroscopy (FTIR). The yields of primary reaction products in the absence of NO were: 5-chloro-2(5H)-furanone (64.5±10.7)%, E-butenedial (11±3)%, 5-hydroxy-2(5H)-furanone (2.4%) and Z-butenedial (1.6±0.5)%. Other products generated by secondary reactions were 2(3H)-furanone (2.8±1.9)%, HCl (21.1±3%) and CO. Maleic anhydride was detected with a yield of about 2%, however, this yield may be a combination of both primary and secondary reactions. All errors are ±2σ. The observed products confirm that addition of Cl atoms to the double bond of furan is the dominant reaction pathway. – Atmospheric Environment (2007) vol. 41 (38) pp. 8796-8810

Solvent-Free Thermal and Microwave-Assisted [3 + 2] Cycloadditions between Stabilized Azomethine Ylides and Nitrostyrenes. An Experimental and Theoretical Study

Ana Arrieta, Dorleta Otaegui, Aizpea Zubia, Fernando Cossio, Angel Diaz-Ortiz, Antonio de la Hoz, M Herrero, Pilar Prieto, Concepcion Foces-Foces, Jose Pizarro, Maria Arriortua. The stereochem. outcomes obsd. in the thermal and microwave-assisted [3 + 2] cycloaddn. between stabilized azomethine ylides and nitrostyrenes have been analyzed using exptl. and computational approaches.  It has been obsd. that, in the absence of solvent, three stereoisomers are formed, both under classical heating conditions and under microwave irradn.  This result contrasts with that obsd. in soln. under classical thermal conditions.  The 4-nitropyrrolidines obtained in this way can be aromatized under further microwave irradn. to yield mixts. of pyrroles and 4-nitropyrroles.  It is found that ground state cycloaddns. between imines and nitrostyrenes take place by three-step mechanisms.  The first step involves enolization of the starting imine, and this is followed by a pseudopericyclic 10-electron [1.4]-hydrogen shift.  Finally, the cycloaddn. takes place by a relatively asynchronous arom. six-electron supra-supra thermal mechanism. – J. Org. Chem. (2007) vol. 72 (12) pp. 4313-4322

Microwave-assisted reactions in heterocyclic compounds with applications in medicinal and supramolecular chemistry

Antonio de la Hoz, Angel Diaz-Ortiz, Andres Moreno, Ana Sanchez-Migallon, Pilar Prieto, Jose Carrillo, Ester Vazquez, Ma Gomez, Ma Herrero. A review.  Microwave irradn. was successfully applied in org. chem.  Spectacular accelerations, higher yields under milder reaction conditions and higher product purities were all reported.  Indeed, a no. of authors described success in reactions that do not occur under conventional heating and modifications in selectivity (chemo-, regio- and stereoselectivity) were even reported.  Recent advances in microwave-assisted combinatorial chem. include high-speed solid-phase and polymer-supported org. synthesis, rapid parallel synthesis of compd. libraries, and library generation by automated sequential microwave irradn.  In addn., new instrumentation for high-throughput microwave-assisted synthesis continues to be developed at a steady pace.  The impressive speed combined with the unmatched control over reaction parameters justifies the growing interest in this application of microwave heating.  In this review the authors highlighted their recent advances in this area, with a particular emphasis on cycloaddn. reactions of heterocyclic compds. both with and without supports, applications in supramol. chem. and the reproducibility and scalability of org. reactions involving the use of microwave irradn techniques. – Comb. Chem. High Throughput Screening (2007) vol. 10 (10) pp. 877-902

Editorial

Angel Diaz-Ortiz, Antonio de la Hoz. Comb. Chem. High Throughput Screening (2007) vol. 10 (9) pp. 733-734

Meet the guest editors

Angel Diaz-Ortiz, Antonio de la Hoz. Comb. Chem. High Throughput Screening (2007) vol. 10 (10) pp. 933

Review on non-thermal effects of microwave irradiation in organic synthesis Antonio de la Hoz, Angel Diaz-Ortiz, Andres Moreno. The aim of this review is to show the occurrence of non-thermal effects in organic synthesis.  The effect of microwave irradiation is a consequence of the interaction of radiation with matter and a combination of thermal and non-thermal effects.  Thermal effects are well-described and arise from the heating rate, sometimes non accessible by conventional heating, superheating, “hot spots” and the selective absorption of radiation by polar substances.  The existence of non-thermal effects of the highly polarized radiation is still a controversial topic, and one usually masked by thermal effects.  Separation and identification of thermal and non-thermal effects is a complex matter, but essential to the study of non-thermal effects.  Some predictive models have also been described. – J Microw Power Electromagn Energy (2007) vol. 41 (1) pp. 44-64

Green and chemoselective oxidation of sulfides with sodium perborate and sodium percarbonate: nucleophilic and electrophilic character of the oxidation system

M Gomez, Ruben Caballero, Ester Vazquez, Andres Moreno, Antonio de la Hoz, Angel Diaz-Ortiz. An efficient, chemoselective and environmentally friendly procedure for the oxidn. of sulfides is described.  Reactions are carried out using sodium perborate or sodium percarbonate as the oxidant, solvent-free conditions or water as the reaction medium and microwave irradn. or conventional heating as the energy source.  A comparative study concerning the effect of the oxidant and reaction conditions on yield and chemoselectivity (sulfoxide vs. sulfone) has been carried out.  In the solid phase, the nature of the solid support or catalyst has a more marked influence than the oxidant on the electrophilic and nucleophilic character of the oxidn. – Green Chem. (2007) vol. 9 (4) pp. 331-336

Reproducibility and scalability of solvent-free microwave-assisted reactions: from domestic ovens to controllable parallel applications

Angel Diaz-Ortiz, Antonio de la Hoz, Jesus Alcazar, Jose Carrillo, Maria Herrero, Alberto Fontana, Juan de Mata. The heating of different parallel arrays in domestic ovens offers the possibility to perform multiple reactions in one irradn. expt., blending the advantages of microwave heating technol. and parallel chem.  However, they are usually performed without an appropriate temp. control; thus, reproducibility becomes a major issue limiting the application of such reactions.  This is exemplified when working at a different scales or using different instruments.  For the first time a typical solvent-free reaction described in a domestic oven has been reproduced in a monomode reactor, scaled up in a controlled multimode oven and reproduced in parallel; 24 reactions were carried out in a well plate.  Parallel reactions were performed in a Weflon multiwell plate to assure identical conditions for each individual reaction.  As many reactions under microwave irradn. have been performed in solvent-free conditions, this result opens new possibilities in reproducibility, scalability and combinatorial chem. and permits to take advantage of many synthetic procedures described in domestic ovens. – Comb. Chem. High Throughput Screening (2007) vol. 10 (3) pp. 163-169

Microwave in High Throughput Synthesis (Part 1)

Antonio de la Hoz, Angel Diaz-Ortiz, Editors. Comb. Chem. High Throughput Screening, 10(9) (2007) pp. 68 pp.

 

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