The bromination of 4,5-dimethyl-1,3-dioxolen-2-one (I) with N-bromo-succinimide (NBS) and azobisisobutyronitrile (AIBN) in CCl4 gives 4-methyl-5-bromomethyl-1,3-diioxolen-2-one (II), which is then condensed with ampicillin (III) by means of KHCO3 and benzaldehyde in DMF.