PURPOSE: To obtain the titled compound useful as a synthetic intermediate, etc. for an ameliorant of sequelae due to the cerebral thrombosis easily in high yield, by the intramolecular alkylation of a specific acetoacetic ester derivative.

CONSTITUTION: An acetoacetic ester derivative of formulaI[X is halogen or RSO2O (R is alkyl or aryl); n is an integer 1W4]is subjected to the intramolecular alkylation to give an α-acetyllactone of formula II. The intramolecular alkylation is carried out in the presence of an alkali metal, e.g. Li, or a basic substance, e.g. NaH, in a solvent, e.g. benzene or THF. Preferably, a metallic iodide, e.g. NaI, or crown ether is used for increasing the reaction yield.