1-Ethoxy-3-trifluoromethyl-1,3-butadiene and its 2-bromo- and 2-phenyl-substituted derivs. have been prepd. by Wittig methylenation of the corresponding 4-ethoxy-1,1,1-trifluoro-3-buten-2-ones, which in turn are readily accessible from trifluoroacetic acid. The electron-rich/electron-poor dienes combine smoothly with di-Me acetylenedicarboxylate and Me propiolate to provide trifluoromethyl-substituted phthalates or benzoates. Satisfactory yields of 4-(trifluoromethyl)pyridinecarboxylic acids can even be achieved with Me cyanoformate, a less reactive dienophile, if a large excess of the dienophile is employed. [on SciFinder (R)]