An assessment of the technique of simultaneous cooling in conjunction with microwave heating for organic synthesis

Leadbeater, Nicholas E.; Pillsbury, Sharon J.; Shanahan, Erik; Williams, Victoria

doi:10.1016/j.tet.2005.01.105

Cited by 81 publications

(55 citation statements)

References 44 publications

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“…These equipments have new tools, such as simultaneous external cooling of the reaction mixture (maintaining below room temperature), in this case, the reaction vessel is cooled from the outside by compressed air or with the aid of a cooling fluid while being irradiated by microwaves. 11,12 This allows a higher level of microwave power to be directly administered to the reaction mixture but will prevent overheating by continuously removing heat. 11,12 According to some studies, transformations of this type involving polar intermediates or transition states are likely to be accelerated by microwave irradiation due to a specific interaction of the electric field with the polar reaction species, which is not connected to the reaction temperature.…”

Section: Introductionmentioning

confidence: 99%

“…11,12 This allows a higher level of microwave power to be directly administered to the reaction mixture but will prevent overheating by continuously removing heat. 11,12 According to some studies, transformations of this type involving polar intermediates or transition states are likely to be accelerated by microwave irradiation due to a specific interaction of the electric field with the polar reaction species, which is not connected to the reaction temperature. 9 Reactions performed in microwave ovens must be considered in relation to the reaction medium.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Pyrazole synthesis under microwave irradiation and solvent-free conditions

Buriol¹,

Frizzo²,

Marzari³

et al. 2010

J. Braz. Chem. Soc.

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Este trabalho descreve a síntese de 4,5-diidro-1H-pirazóis pela reação de ciclocondensação de hidrazinas [NH 2 NH-R 2 , onde R 2 = CO 2 Me, Ph, CH 2 CH 2 OH] com 4-alcóxi-1,1,1-trifluor-3-alquen-2-onas [CF 3 C(O)CH=C(R 1 )OR, onde R/R 1 = Et/H, Me/Me and Me/Ph] sob irradiação de microondas utilizando um equipamento de micro-ondas para síntese e em condição livre de solvente. Algumas reações foram realizadas na presença de metanol. Os resultados obtidos utilizando micro-ondas para síntese foram comparados com aqueles obtidos quando a reação foi feita pelo método convencional e no forno de micro-ondas doméstico. Os produtos foram obtidos com bons rendimentos em um intervalo de tempo pequeno. Além disso, foi demonstrado que a temperatura da reação alterou a formação dos produtos para cada hidrazina mostrando que o equipamento de micro-ondas para síntese é eficiente para as reações de hidrazinas com 4-alcóxi-1,1,1-trifluor-3-alquen-2-onas levando à formação dos produtos 4,5-diidro-1H-pirazóis e pirazóis. This paper presents a study of solvent-free reaction conditions using microwave irradiation (MW) to obtain 4,5-dihydro-1H-pyrazoles and dehydrated pyrazoles by the cyclocondensation reaction of 4-alkoxy-1,1,1-trifluoro-3-alken-2-ones [CF 3 C(O)CH=C(R . Some reactions were performed under the same reaction conditions using methanol as solvent. The results obtained using MW equipment for synthesis under solvent-free conditions were also compared with those described in literature for conventional thermal heating and heating with a domestic MW oven. In general, the products furnished by reaction in MW equipment for synthesis presented better yields and shorter reaction times. In addition, it was demonstrated that the reaction temperature altered the formation of products for each hydrazine showing that MW equipment for synthesis is efficient for reacting hydrazines and 4-alkoxy-1,1,1-trifluoro-3-alken-2-ones to procedure the products 4,5-dihydro-1H-pyrazoles and dehydrated pyrazoles.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Pyrazole synthesis under microwave irradiation and solvent-free conditions

Buriol¹,

Frizzo²,

Marzari³

et al. 2010

J. Braz. Chem. Soc.

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“…13 The best conditions gave conversions of 65% and these were obtained at 170 C without external cooling. Higher temperatures produced a clear reduction in yield and a charred reaction mixture was obtained at 200 C. A series of N-aminides 2e-g, 2i-k, 2o-q, 2s, 2u-v, 2x-z, and 2aa (see Table 1, method C) were synthesized according to this green methodology (Scheme 2), which reduces reaction times from hours (4-39 h) to 10 min without appreciable changes in yield.…”

Section: Resultsmentioning

confidence: 96%

“…1 H NMR spectra were recorded on Varian Unity 300 (300 MHz) and Varian Mercury-VX (500 MHz) spectrometers at ambient temperature. 13 C NMR spectra were recorded on Varian Unity 300 (75 MHz) and Varian Mercury-VX (125 MHz) spectrometers at ambient temperature. Chemical shifts are given in parts per million (d) downfield from TMS.…”

Section: General Remarksmentioning

confidence: 99%

New approaches to the synthesis of pyridinium N-heteroarylaminides

2008

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a b s t r a c tDifferent substituted pyridinium N-heteroarylaminides have been prepared in one step from N-aminopyridinium iodide and the corresponding heteroaryl halide by two alternative routes. The use of Pd catalysis allowed the easy preparation of products from the less reactive haloheterocycles. The use of water as a solvent in conjunction with microwave heating dramatically diminishes the reaction time without having an adverse effect on reaction yields.

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“…It enables a greater MW power level to be applied directly to the reaction mixture and prevents overheating. Some results have appeared [111,112] but are limited to savings in reaction time, but promising results could also be expected for selectivity, particularly in asymmetric induction, which usually needs low temperatures.…”

Section: Effects On Selectivitymentioning

confidence: 99%