GENERAL METHODS: Synthesis of 5-phenylpent-2,4-dienoic acid (Scheme 1) followed the Knoevenagel condensation reaction. Cinnamaldehyde (0.01 mol) was dissolved with malonic acid (0.01 mol) in 1.12 mL of a solvent mixture of pyridine and piperidine (0.01 mol). The reaction mixture was heated to reflux until carbon dioxide gas stopped escaping. Upon completion of the reaction, the reaction solution was poured into a mixture containing 2N HCl and ice, and the precipitate precipitated was collected by filtration and recrystallized from pure water or a 3:1 water/ethanol solvent mixture. If no precipitate is produced, the aqueous phase is extracted with 3 x 100 mL of chloroform or dichloromethane, the organic phases are combined, dried with anhydrous magnesium sulfate, concentrated to dryness under reduced pressure, and the resulting residue is purified by recrystallization from aqueous ethanol.
[1] Molecules, 2014, vol. 19, # 7, p. 9655 - 9674
[2] Chemistry - A European Journal, 2017, vol. 23, # 3, p. 554 - 557
[3] Organic Letters, 2017, vol. 19, # 23, p. 6412 - 6415
