The indirect electroteduction with (PhSe)(2) as a recyclable mediator is applied to complete dehalogenation of alpha,alpha -dibromolactams, giving useful intermediates in the synthesis of beta -lactamase inhibitors. The electrolysis can be carried out with 2 mol% of (PhSe), in a MeOH/0.2 M NaClO4/(Pt) system using a Nafion (R) -separated divided cell. The reaction is considered to proceed stepwise by forming mono-debromination products, i.e. alpha bromo-beta -lactams as intermediates, and then further debromination products.