Abstract: A process for preparing a compound of the formula ##STR1## in which both Rs and H or OH; comprising the steps a. of treating the ethyl ester of caffeic acid with trialkylsilyl chloride at ambient conditions in equimolar proportions in the presence of a base;b. the reduction of the ester to the corresponding allylic alcohol with aluminum hydride reagent;c. of oxidizing the resulting product with manganese dioxide at ambient temperature and in excess molar proportion to yield the corresponding allylic aldehyde;d. of coupling the latter with the silyl ether of the relative phenyl acetylide; ande. of hydrolysis of this coupled product with alkylammonium fluoride at ambient conditions in equimolar proportions.