The reactions of 2-(trifluoromethyl)propenoic acid (I) with unsaturated Grignard reagentshave been examined. Vinylmagnesium bromide with I gave 2-difluoromethylene-4-pentenoicacid (II) and analogous acids were obtained from propenyl and butenyl magnesiumhalides. The iodolactonization of II gave 2-difluoromethylene-4-iodomethyl-γ-lactone (III).2-Monofluoromethylene-4-penten-1-ol (IV) was obtained by