Abstract
A series of new quinazoline-4(3H)-one derivatives (2-16) have been synthesized using methyl α-[(4-oxoquinazolin-2-yl)thio]acetate (1) as precursor. The corresponding hydrazide (2) and thiosemicarbazide (4) were synthesized from this ester via the reaction of the ester (1) with hydrazine hydrate and with ammonium thiocyanate respectively. The thiosemicarbazide (4) was employed to synthesize 2-amino-1,3,4-thiadiazole (5) and 1,3,4-triazole-5-thiol (6) via its cyclization under acidic and basic conditions respectively. On the other side, the reaction of the organic thiocyanates with the hydrazide (2) would be afforded di-substituted thiosemicarbazide (13-15), while the reaction of carbon disulfide with the hydrazide (2) in existence of potassium hydroxide afforded the carbodithioate potassium salt (7). The carbodithioate potassium salt (7) was treated with hydrazine hydrate to give the 1-amino-1,3,4-triazol-2-thiole compound (8). The later compound (8) was used as a precursor to synthesize fused heterocyclic compounds {namely 1,2,4-triazolo[3,4,b][1,3,4]thiadiazolin-6-thiol (9), 1,2,4-triazolo[3,4,b][1,3,4]-6-methylthiadiazoline (10) and 1,2,4-triazolo[3,4,b][1,3,4]-6-arylthiadiazoline (11, 12)} via the reaction of compound (8) with CS2 / potassium hydroxide, acetyl chloride and aromatic aldehydes respectively. Elucidation of the structures of the compounds (4-16) was performed using FT-IR, 1H-NMR and 13C-NMR spectroscopic methods.