α-Methylene γ -lactone fused to seven-membered carbocycle was synthesized by intramolecularcyclization of (2-ethoxycarbonylallyl)trimethylsilane or (2-acetoxymethylallyl)trimethylsilane with acidchloride. The former was found to be a better way for seven-membered carbocyclization, while the latter method was applicable to the synthesis of α- methylene γ -lactones fused to eight- and fourteen-membered carbocycles