PURPOSE: To obtain the subject derivative, excellent in productivity and useful as an intermediate for agricultural chemicals, medicines, etc., by heating an oxazolidine-2-thione derivative, etc., expressed by a specific structure at a prescribed temperature or above.

CONSTITUTION: An oxazolidine-2-thione derivative expressed by formula I [X1 to X4 are H, (halogen-substituted)alkyl or (halogen-substituted)aryl] or its salt is heated in the presence of a basic substance such as sodium hydroxide in a solvent such as DMF at ≥50°C, preferably ≥70°C to afford the objective derivative expressed by formula II.