A novel and efficient aziridination of α-halo ketones is reported. The reaction of α-halo ketones with diethyl N-arylphosphoramidates affords diethyl N-aryl-N-(2-oxoalkyl) phosphoramidates which undergo reductive (H−-induced) cyclization with sodium borohydride followed by sodium hydride to give 1, 2-disubstituted and 1, 2, 3-trisubstituted aziridines. The cyclization induced by NCS− or PhS− affords substituted aziridines ...