We have studied the electronic effect of substituents, steric factors, the medium, and the nature of the oxidizing agent on oxidative cyclocondensation of 2-thioxo-4-quinazolone and its substituted derivatives. We have found that electron-donor substituents promote the reaction while electronacceptor substituents inhibit the reaction.Keywords: 8H,15H-1,2,4-thiadiazolo[3,2-b:5,4-b']diquinazoline-8,15-dione, 2-thioxo-4-quinazolone, quinazoline-2,4-dione, oxidative cyclocondensation, electronic substituent effects.A rather large number of methods are known for obtaining 1,2,4-thia(seleno)diazoles from aliphatic thio(seleno)amides [2-5], thioureas [6-9], thiocyanates and their derivatives [10,11], amidines, amidoximes and amidinothioureas [12][13][14], isothioureas [15], thiobiurets and thioguanidines [2,16], thiatriazoles, dithiazoles, oxazarines and heterocumulenes [17][18][19][20][21]. The simplest and most accessible method has proven to be the one based on oxidation of thioamides and thioureas. Synthesis from amidino derivatives can be considered as an intermediate step in obtaining them from thioureas and thioamides. The mechanism for the formation of 1,2,4-thia(seleno)diazoles from thioamides and thioureas has not yet been studied in detail. The effect of various factors on the course of the reaction also has not been studied (electronic effects of substituents, steric factors, temperature, the nature of the solvent, the oxidizing agent, etc.). These reactions have not been generally studied for cyclic thioureas. As far as 1,2,4-selenodiazoles are concerned, only their synthesis from selenobenzamides [22,23] and amidines [11] has been described. Only a few derivatives in this class of compounds have been synthesized.Cyclic thio(seleno)ureas are a huge class of heterocyclic compounds. Pyrimidinones (the cyclic analogs of thio(seleno)ureas) condensed with benzene, thiophene, and pyridine rings are of considerable interest for theoretical organic chemistry, in connection with their existence in various tautomeric forms.A large number of derivatives of these compounds have been synthesized so far. They include substances having pesticidal and also other types of physiological activity. _______ * For Communication 3, see [1].
