The photoreactions of diketene with maleic anhydride (4) and dimethylmaleic anhydride (6) gave 2-oxo-1-oxaspiro [3.3] heptane-cis-5, 6-dicarboxylic anhydride (5a, b) and 5, 6-dimethyl-2-oxo-1-oxaspiro [3.3] heptane-cis-5, 6-dicarboxylic anhydride (7a, b), respectively. Treatment of compounds 5 and 7 with hydrogen chloride in ethanol and methanol afforded the corresponding dialkyl 5-alkoxycarbonyl-3-oxoheptanedioate derivatives (8 and 10) and (9 and 11), respectively.