Process for preparing beta lactam compound

A process for preparing an exo-methylenepenam compound of formula (5)

• wherein R1 is selected from the group consisting of hydrogen, amino and protected amino;
• R2 is selected from the group consisting of hydrogen, halogen, C1-4 alkoxy, formyl, acetyl, propionyl, butyryl, isobutyryl and C1-4 alkyl which is substituted by hydroxyl or protected hydroxyl;
• and R3 is hydrogen or a carboxylic acid protecting group, the process comprising:
• subjecting a β-lactam halide compound of formula (2)
• wherein R1, R2 and R3 are as defined above, R4 is aryl or substituted aryl;
• X is halogen;
• Y is selected from the group consisting of a halogen atom, a substituted or unsubstituted lower alkylsulfonyloxy group, a substituted or unsubstituted aromatic sulfonyloxy group, a substituted or unsubstituted halogenated lower alkyl sulfonyloxy group, a substituted or unsubstituted lower alkylphosphoryloxy group and a substituted or unsubstituted aromatic phosphoryloxy group;
• and n is 0 to 2,
• to an electroreduction reaction in a reaction system comprising a positive electrode and a negative electrode, to obtain the exo-methylenepenam compound of formula (5).