(matrix presented) from (S,aS) 2,3-cis:trans = 79:21-89:11 (76-93% yield) from (S,aR) 2,3-cis:trans = 91:9-99:1 (50-99% yield) Novel stereoselective synthesis of 2,3-cis-2-ethynylaziridines from amino allenes is presented. While sodium hydride mediated intramolecular amination of (4S,aS)-4-alkyl-4-[N-(arylsulfonyl)amino]-1-bromobuta-1,2-dienes yields a mixture of 2,3-cis- and 2,3-trans-2-ethynylaziridines in which the cis-isomer predominates (79:21-89:11), the amination of (4S,aR)-isomers affords 2,3-cis-aziridines in excellent selectivities (91:9-100:0). Conversion of 2,3-trans-2-ethynylaziridines into the corresponding cis-isomers via a sequence of reactions (methanesulfonic acid mediated ring-opening reaction, bromination, and aziridination) is also described.