A computational approach to the synthesis of 1,3,5-thiadiazinane-2-thiones in aqueous medium: theoretical evidence for water-promoted heterocyclization.

Based on experimental evidence and DFT studies, a probable cyclization route to 1,3,5-thiadiazinanes-2-thiones in aqueous medium is proposed. Experimental facts suggest the formation of a {[hydroxymethyl (substituted) carbamothioyl] sulfanyl}methanol intermediate via reaction of dithiocarbamate (DTC) and formaldehyde. Nucleophilic addition of glycine to this intermediate generates an adduct that undergoes intramolecular heterocyclization via an S(N)2 reaction. Computational calculations predict an active role of water in the reaction mechanism that promotes intramolecular cyclization.