Synthetic method of caffeic acid phenethyl ester by heck reaction

Many caffeic acid ester compounds are known because of their various pharmacological activities, with great commercial values such as medicine, health-care products and functional foods, especially caffeic acid phenethyl esters. Existing synthetic methods for caffeic acid esters, such as “acyl halide”, the alkylation, catalytic esterification, condensation agent method, Wittig reaction and Knoevenagel condensation, present certain limitation for their wide use. This research aims to explore a synthetic method with versatile conditions for caffeic acid esters by Heck reaction using commercially available materials. A total of three steps were operated to synthesize caffeic acid phenethyl ester (CAPE) protecting reaction, Heck reaction and de-protecting reaction, with 4-bromocatechol and acrylic acid phenethyl alcohol ester as starting materials. CAPE was obtained in a moderate yield of 40% under the optimized conditions of Heck reaction, which were V(Toluene):V(DMF)=4:1, Pd(OAc)₂ (0.05 mmol), Ph₃P (0.15 mmol), NEt₃ (2 mmol), reaction temperature of 90 ℃ and reaction time of 24 h. Compared with the exising synthestic methods, the new method of constructing caffeic acid ester by Heck reaction developed in this work had advantages of versatile conditions, commercially available materials and simple synthetic steps.