Pyrazole synthesis under microwave irradiation and solvent-free conditions

Abstract

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.

Synergic Effects of Ionic Liquid and Microwave Irradiation in Promoting Trifluoromethylpyrazole Synthesis

“…For the data of compound 3a-e, 1 H NMR spectra were found to be identical with the one described in Ref. [12,25,26].…”

“…Recently, we have published a number of works related to the minimization of environmental impacts through the use of ionic liquids [9][10][11] or solvent-free reactions [12,13] Electronic supplementary material The online version of this article (doi:10.1007/s10562-011-0571-9) contains supplementary material, which is available to authorized users. and by using ultrasound [14,15] or MW [12,13] to promote the reactions. Our current review about heterocyclic synthesis in ionic liquid [16] has demonstrated that there is a lack of reports dealing with pyrazole synthesis in this media.…”

The effect of pressurized carbon dioxide on the cyclocondensation reaction between 4-alkoxy-1,1,1-trifluoro-3-alken-2-ones and hydrazines

“…In previous works, using other methodologies as microwave irradiation and/or ionic liquids, this product was obtained as a mixture of 1-phenylpyrazole and the 4,5-dihydropyrazole derivative. 26,27 Analyzing enone 1b,…”

Ionic Liquids as Doping Agents in Microwave Assisted Reactions

“…Several examples have shown that the application of MW irradiation reduces the reaction time, increases the product yield and sometimes results in a different product distribution compared to conventional thermal heating method [1][2][3][4][5][6][9][10][11][12][13][14][15][16][17][18][19][20]. The rate acceleration observed in organic reactions using MW irradiation is due to material-wave interactions leading to thermal and nonthermal effects.…”