A new approach to the synthesis of ⊿^{α, β}-butenolides from γ-butanolides by means of the electrolytic oxidation of α-carboxy-α, γ-dimethyl-γ-butyrolactone (3b) and its α-carboxy-α-methyl analog (3d) resulted in predominant formation of the endocyclic ⊿^{α, β}-isomers, α-methyl-⊿^{α, β}-γ-valerolactone (5a) and α-methyl-⊿^{α, β}-γ-butenolide (5c), accompanied by the exocyclic ⊿^{α, β}-isomers, α-methylene-γ-valerolactone (5b) and α-methylene-γ-butanolide (5d), respectively, under various conditions. The conventional oxidation of α-phenylseleno- (4a) and α-phenylthio-α-methyl-γ-valerolactone (4b) was found to yield a mixture of 5a and 5b. The regiospecific preparation of the endo-isomer (5a) was ultimately achieved by the use of sequential reactions reported earlier, starting from α-methyl-γ-valerolactone (1a) via α-methoxycarbonyl- (3a), α-carboxy- (3b), and α-bromo-α-methyl-γ-valerolactone (3c).