Regioselectivity of Electrophilic Attack on 4-Methyl-1-thioxo- 1,2,4,5-tetrahydro[1,2,4]triazolo[4,3-a]quinazolin-5-one. Part 1: Reactions at the Sulfur Atom

The regioselectivity of the model compound 4-methyl-1-thioxo- 1,2,4,5-tetrahydro[1,2,4]triazolo[4,3-a]quinazolin-5-one (3) towards different electrophiles was studied. Compound 3 reacts with alkyl and aryl halides to give the corresponding S-substituted derivatives. The reaction of the model thioamide with acyl halides proceeds by the formation of kinetically controlled S-acyl derivatives followed by a transacylation reaction to give the N(2)-acyl derivatives as thermodynamically controlled products. Theoretical DFT computational studies supported the explanation of these results. The synthesized compounds were characterized by FTIR, (1)H-NMR, (13)C-NMR, and mass spectroscopy.