An efficient and practical synthesis of N-p-tosyl-aziridine-2-ketones and carboxylates through the use of α,β-unsaturated esters and ketones has been reported. The synthesis was conducted via a one-pot procedure consisting of aminohalogenation and in situ intramolecular SN2 substitution. Triethylamine was found to be an effective base for the in situ cyclization for most substrates. Interestingly, for several enone cases, a slightly modified procedure in which 1.0 equivalent of p-TsNCl2 was slowly added into 2.0 equivalents of enone for aminohalogenation followed by quenching with aqueous Na2SO3 resulted in crude aziridines which were proven to be nearly pure by the crude 1H NMR analysis. Moderate to good yields and excellent anti stereoselectivity were achieved for 21 examples.