Carbocyclic rings fused to an α-methylene-γ-lactone unit were synthesized from ω-formylated β-ethoxycarbonylallyl halides (4a-g) through intramolecular cyclization by the use of a low-valent chromium reagent, prepared from CrCl₃ and LiAlH₄, in N, N-dimethylformamide. α-Methylene-γ-lactones fused to medium (eight-membered) or large (twelve-and fourteen-membered) ring system (5a, c and d) were synthesized by this method in good to fairly good yields. However, the formylated allyl halide (4b), expected to afford a ten-membered carbocyclic ring system, gave dilactones fused to a twenty-membered ring unit even under a high dilution reaction condition.