Abstract
3-Ethoxycabonyl-1,2,4-triazolo[4,3-c]quinazoline (2) has been synthesized in excellent yield by the condensation of 4-hydrazinoquinazoline (1) with diethyl oxalate and was converted into 3-carbohydrazide 3. The later product was treated with potassium thiocyanate, phenylisothiocyanate or carbon disulfide followed by reaction with hydrazine hydrate to give the respective new 1,2,4-triazolo[4,3-c]quinazoline derivatives 4, 8 or 12. Dehydrative cyclization of the later compounds with concentrated sulphuric acid, sodium hydroxide, m-bromobenzoic acid, carbon disulfide, oxalic acid, phenacyl bromide or benzoin yielded the target heterocycles namely, 1,3,4-thiadiazole, 1,2,4-triazole, 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazole or 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazine incorporating 1,2,4-triazolo[4,3-c]quinazoline ring. The structure of the above compounds was confirmed from their spectral characteristics.