Reaction of trialkylamines and diamines with 1,3,5-trichloro-1,2,4,6-cyclothiatriazine, (ClCN)(2)(ClSN), is found to result in the facile cleavage of a C-N bond of the tertiary amine and regiospecific substitution of the dialkylamino group on the carbon atoms of the heterocycle. Reaction of (ClCN)(2)(ClSN) with tetramethylmethylenediamine in diethyl ether at room temperature gives the thiatriazine with dimethylamino groups substituted on the ring carbon atoms, [(Me2N)CN](2)(ClSN) (1). The reaction of triethylamine with (ClCN)(2)(ClSN) gives the diethylamino-substituted heterocycle [(Et2N)CN](2)[S(O)NH] (2) which is partially saturated as a result of the hydrolysis of the S-CI bond. The crystal structure of this compound shows it to be a dimer with hydrogen bonding interactions between the N-H and S=O groups. Reaction of excess morpholine with (ClCN)(2)(ClSN) gives the trimorpholino-substituted compound [(OC4H8N)CN](2)[(OC4H8N)SN] (3). The S-Cl bond of 1 has also been substituted with morpholine to give [(Me2N)CN](2)[(OC4H8N)SN] (4). It is also observed that by using diethyl ether as a solvent, dealkylations can be brought about even at room temperature with these heterocycles.