PURPOSE: To obtain new monofluoro-β-lactams, useful as an intermediate for physiologically active substances such as medicines or agochemicals, functional polymers, etc., according to a new method for directly fluorinating β-lactams.

CONSTITUTION: These monofluoro-β-lactams are expressed by formula I [R1 is H, alkyl, cycloalkyl, benzyl or (substituted)phenyl; R2 is alkyl or (substituted) phenyl], e.g. 1-n-butyl-3-fluoro-3-phenylsulfenyl-2-azetidinone. The compounds expressed by formula I are obtained by electrochemically reacting β-lactams expressed by formula II with fluoride ions. The compounds expressed by formula I can especially be expected as a raw material for antimicrobial agents.