Pyrazoles and their derivatives have attracted particular attention because they have a wide variety of biological activities, and recently, we found that 4,4´-(arylmethylene)-bis-(1-phenyl-3-methyl-1H-pyrazole-5-ols) have good leishmanicidal activity against promastigotes of Leishmania mexicana. 4-Arylidenepyrazolones derivatives also have antiparasitic activity and are the intermediated in the synthesis of these bispirazoles that are formed by the equimolar reaction of 5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one with aromatic aldehydes. In order to obtain new compounds with potential leishmanicidal activity, we want to synthesize several 4-arylallylidenepyrazolones derivatives through the reaction of pyrazol-3-one with different cinnamaldehydes. We report here the synthesis of some 4-arylallylidene derivatives from the reaction between 5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one and substituted cinnamaldehydes. Using the reaction of 4-nitrocinnamaldehyde as a model, we found that L-proline and FeCl₃ are the best catalysts, and also we observed a solvent effect in the reaction. Our preliminary results indicate that aprotic solvents favor the formation of the 2Z isomer instead the 2E isomer.