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 N²-acyl derivatives as thermodynamically controlled products. Theoretical DFT computational studies supported the explanation of these results. The synthesized compounds were characterized by FTIR, ¹H-NMR, ¹³C-NMR, and mass spectroscopy.

N-(2-Cyanophenyl)chloromethanimidoyl chloride (3) was prepared from 2-isothiocyanatobenzonitrile by the reaction with sulfuryl chloride or gaseous chlorine in an inert solvent. It was found that N-(2-cyanophenyl)chloromethanimidothioic chloride (2) and bis[N-(cyanophenyl)chloromethanimidoyl] sulfide (7) are intermediates of this reaction. The chloride 3 was obtained also by a three-component one-pot reaction of N-(2-cyanophenyl)-formamide in the present of thionyl chloride and sulfuryl chloride. (2-Cyanophenyl)-(1-{[(2-cyanophenyl)-imino]methoxy}methylidene)ammonium chloride (6) was detected as a by-product of this reaction. Identity of all reaction products was confirmed by GC-MS, FTIR, ¹H and ¹³C NMR spectroscopy.

The reaction of N-(2-cyanophenyl)benzimidoyl chloride with reagents containing a thioamide moiety, i.e. thioacetamide, benzylthiourea, symmetrical dialkyl- and diarylthioureas gave different cyclic products: 3,1-benzothiazine, 1,3,5-benzotriazocine and quinazoline. The reaction pathways of prepared compounds are discussed.

The regioselectivity on a cyclic thioamide group towards different electrophiles was studied on the model compound 4-methyl-1-thioxo-1,2,4,5-tetrahydro[1,2,4]triazolo [4,3-a]quinazolin-5-one 1. The examined compound 1 reacts with alkyl halides, amines in the presence of formaldehyde, acyl halides and compounds having activated double bonds to afford the N-substituted derivatives 2, 3 and 6. The regioselective reactions on nitrogen atom are due to strong Coulombic attraction. The reaction of 1 with amines in the presence of hydrogen peroxide afforded the aminolysis product 4. Compounds 1-6 were identified by FTIR, 1H NMR, 13C NMR, and mass spectroscopy.

1,1-Disubstituted-3-(2-phenyl-3H-quinazolin-4-ylidene)thioureas (8) were synthesized in a one pot reaction of N-(2-cyanophenyl)benzimidoyl isothicyanate (3) with secondary amines. The products underwent transamination reactions. Compounds 8a-8g were identified by FTIR, ¹H-NMR, ¹³C-NMR, mass spectroscopy and X-ray crystallography.

1-substituted-3-(2-phenylquinazolin-4-yl) thioureas (7) were produced by an intramolecular cycloaddition reaction of 1-substitued-3-[(2-cyanophenylimino) phenylmethyl] thioureas (3). These compounds in turn were prepared by the reaction of N-(2-cyanophenyl)benzimidoyl isothiocyanate (2) with primary amines. The structures of products 7 were confirmed by FTIR, ¹H-NMR, ¹³C-NMR, mass spectroscopy and X-ray crystallography.