The synthesis of series of fused diaziridines, which are difficult to access by existing methods, was achieved by the reaction of cyclic secondary amines with p-toluenesulfonamide in the presence of N-bromosuccinimide (NBS) and a suitable base. This oxidation system enables the efficient in-situ formation of key intermediates which are N-bromoamines (a precursor of cyclic imines) and N-bromosulfonamides. In addition, an alternative method using N-bromo-N-sodio-p-toluenesulfonamide (bromamine-T) in the presence of a catalytic amount of CF3CO2H for the synthesis of fused diaziridines is also reported.