N,N-Dichloro-o-nitrobenzenesulfonamide (2-NsNCl2) was found to be an effective electrophilic nitrogen source for the direct diamination of α,β-unsaturated ketones without the use of any metal catalysts. The reaction is very convenient to carry out without the protection of inert gases. Molecular sieves (4 Å) and temperature were found to play key roles in controlling the formations of 3-trichloromethyl and dichloromethyl imidazoline products (16 examples). The 2-Ns-protection group of the resulting diamine products can be easily cleaved under mild Fukuyama's conditions. A new mechanism hypothesis of [2+3] cyclization and N-chlorination has been proposed to explain the product structures, particularly their regio- and stereochemistry.