Selective dehalogenation of 6,6-dibromopenicillanates by indirect electroreduction with diphenyl diselenide as a recyclable mediator

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