3-Amino-2-thioxo-1,2,3,4-tetrahydroquinazolin-4-one (1) contains two reactive centers -thioxo and amino groups -and can be used for the synthesis of condensed heterocycles [1][2]
[3][4][5], including some with antihypertonic, antibacterial, and fungicidal properties [4,5]. Hence it is a timely synthetic problem to prepare new heterocycles containing the quinazolin-4-one unit.
The aim of the present study was the synthesis of 2-aryl-5H-[1,3,4]thiadiazolo[2,3-b]quinazolin-5-ones, which, using the general methods for the synthesis of condensed systems containing 1,3,4-thiadiazole [6], may be obtained by the condensation of compound 1 with carboxylic acids in the presence of dehydrating agents, and also by the oxidative cyclization of 3-arylmethylidenamino-2-thioxo-1,2,3,4-tetrahydroquinazolin-4-ones.
We have established that 2-aryl-5H-[1,3,4]thiadiazolo[2,3-b]quinazolin-5-ones 3a-e are formed when compound 1 was heated with aromatic carboxylic acids 2a-e in POCl 3 for 2 h. The yields of 3a-e were 66-73%.
In the 1 H NMR spectra of compounds 3a-e there are characteristic signals of the protons of the quinazoline and aromatic rings (7.11-8.41 ppm), while absorption bands for the C=O and C=N groups (1690-1710 and 1580-1610 cm -1 respectively) were observed in their IR spectra.
3-Arylmethylidenamino-2-thioxo-1,2,3,4-tetrahydroquinazolin-4-ones 5a-d were obtained in 67-79% yields by the reaction of compound 1 with the aromatic aldehydes 4a-d in acetic acid.