Highly efficient racemisation of a key intermediate of the antibiotic moxifloxacin

N-Chlorination by sodium dichloroisocyanurate and dehydrochlorination by TEA, followed by hydrogenation, allowed (1R,6S)-8-benzyl-7,9-dioxo-2,8- diazabicyclo[4.3.0]nonane to be quantitatively racemised and the resulting trans-free cis racemate to be recycled into the resolution process to yield (1S,6R)-8-benzyl-7,9-dioxo-2,8-diazabicyclo[4.3.0]nonane, a key intermediate of moxifloxacin.