Study on Trifluoromethanesulfonic Acid-Promoted Synthesis of Daidzein: Process Optimization and Reaction Mechanism

Daidzein has been widely used in pharmaceuticals, nutraceuticals, cosmetics, feed additives, etc. Its preparation process and related reaction mechanism need to be further investigated. A cost-effective process for synthesizing daidzein was developed in this work. In this paper, a two-step synthesis of daidzein (Friedel-Craft acylation and [5+1] cyclization) was developed via the employment of trifluoromethanesulfonic acid (TfOH) as an effective promoting reagent. The effect of reaction conditions such as solvent, the amount of TfOH, reaction temperature, and reactant ratio on the conversion rate and the yield of the reaction, respectively, was systematically investigated, and daidzein was obtained in 74.0% isolated yield under optimal conditions. Due to the facilitating effect of TfOH, the Friedel-Craft acylation was completed within 10 min at 90 °C and the [5+1] cyclization was completed within 180 min at 25 °C. In addition, a possible reaction mechanism for this process was proposed. The results of the study may provide useful guidance for industrial production of daidzein on a large scale.