Difluorodienes result from the double dehydrobromination of 4-aryl-1,3-dibromo-1,1-difluorobutanes with DBU. Attempted syntheses of analogous 4-alkyl or 4-alkoxy dienes yield monoelimination products under mild conditions and unexpected trifluoro compounds under more vigorous conditions. 4-Aryl-1,1-difluoro-1,3-butadienes react rapidly with 4-phenyl-1,2,4-triazoline-3,5-dione in Diels-Alder reactions, but these dienes are unreactive toward several other electron-deficient and electron-rich dienophiles.