The synthesis of 1, 1, 1-trihalo-4-methoxy-4-[2-thienyl]-3-buten-2-ones, 1, 1, 1-trihalo-4- methoxy-4-[2-furyl]-3-buten-2-ones and the respective trihalomethyl 1, 3-butanone derivatives by trihaloacylation of dimethoxy acetals derived from 2-acetylthiophene and 2- acetylfuran are reported. This is a convenient method to obtain fluorinated and chlorinated 1, 3-dielectrophiles from 2-acetylthiophene and 2-acetylfuran. The fluorinated 1, 3- ...