A series of octahydro-2H-pyrazino[1,2-a]pyrazines (1,4,8-triazabicyclo[4.4.0]decanes), 7 have been prepared by a new and efficient method starting from 1,4-dibenzyl-2-ethoxycarbonylpiperazine (1). The target compounds are precursors of a new series of antibacterial quinolones.