A new nitrogen source combination was found for the regio- and stereoselective diamination of α,β-unsaturated ketones. This combination employs the readily available and inexpensive combination of NCS and 2-NsNH 2 as the electrophilic nitrogen source, and acetonitrile as the nucleophilic nitrogen source, respectively. The reaction is easily performed by mixing olefin, 2-NsNH 2, NCS and 4 Å molecular sieves in freshly distilled acetonitrile at room temperature. The reaction is chemoselective without the formation of any haloamine side products. A new aziridinium ion formed from enones and 2-NsNHCl is suggested to exist and to react with nitrile via a [2+3] cycloaddition mechanism, which is responsible for the excellent regio-, stereoselectivity of the resulting diamination products. The regio-, stereo- and chemoselective imidazolination of enones has been established by using the new combination of 2-NsNH 2/NCS as the electrophilic nitrogen source and MeCN as the nucleophile. The reaction is very convenient to carry out simply by mixing olefin, 2-NsNH 2, NCS and 4 Å molecular sieves in freshly distilled acetonitrile at room temperature. The aziridinium ion formed from the reaction of 2-NsNCl with olefins and the corresponding [2+3] cycloaddition are proposed during the reaction process to control regio- and stereoselectivity.