To obtain the subject compound for synthetic raw materials, etc., of β-lactamase inhibitors in high yield by reducing a specific cephem compound with a metal having a specific standard oxidation-reduction potential and a metal compound having a standard oxidation-reduction potential higher than that of the metal.
A cephem compound represented by formula I [R1 is H or a (protected)amino group; R2 is H, a halogen, a lower alkoxy, a lower acyl, a (substituted)lower alkyl or a (protected)hydroxyl group; R3 is H or a carboxylic acid protecting group; X is a halogen, a (substituted)lower alkylsulfonyloxy, an arylsulfonyloxy or a halogenated sulfonyloxy] is reduced with an at least equimolar metal having ≤-0.3(V/SCE) standard oxidation- reduction potential and 0.0001-10mol (based on 1mol cephem compound) metal compound having a standard oxidation-reduction potential higher than that of the metal to provide the objective exomethylenepenam represented by formula II useful as a synthetic intermediate, etc., of β-lactamase inhibitor in high yield and purity.
TANAKA HIDEO
KAMEYAMA YUTAKA
TOKUMARU YOSHIHISA
