3- -l,2,4-triazolo

The reaction of 2,3-diaminoquinazolin-4-one 404 with aryl aldehydes and thioglycolic acid gives 2-substituted 1,3-dihydro-thiazolo[3, 4 2,3][l,2,4]triazolo[5,l-A]quinazolin-5-ones 405 (Equation 79) <2004MI10>. 

Aryl-3-phenacylthio-l,2,4-triazoles 122 react with carbon disulfide and aryl isothiocyanates to give 5-aryl-3//-[l,2,4]triazolo[3,4-f][l,2,4]dithiazole-3-thiones and the 3-arylimino derivatives 123 (Equation 35) <1983ABC1017>. 

Heating l-amino-2-methylaminobenzimidazole (280) with formamide or triethyl orthoformate in acetic anhydride affords 3-methyl-3//-[l,2,4]triazolo[l,5-a]benzimidazole (281) (Equation (77)) <87KGS278, 88KGS1070, 89KGS209>. 

Aryl-2-(carboxymethyl)(or carboxyethyl)thiazolo[3, 4 2,3]-l,2,4-triazolo[5,4-3]-l,3,3-thiadiazines 234 are obtained from 2-aryl-3-thioureido-4-thiazolidinones 235, which are formed by the addition-condensation of aldehyde thiosemi-carbazones 237 and mercaptoacetic acid. Compounds 235 undergo chemoselective intramolecular heterocyclizations to 5-aryl-2-mercapto-l,5-dihydrothiazolo[3,4- ]-l,2,4-triazoles 236, which in turn undergo condensation with a-amino acids to yield 1,3,5-thiadiazines 234 (Scheme 44) <1994JFA811>. 

Some of these polycyclic compounds were found to have moderate activity against Gram-positive and Gram-negative bacteria as well as fungi (13ARK282). 1,2-Diaminopyridone underwent cyclocondensation reactions to provide a number of pyrido[T,2 2,3][l,2,4]triazolo[l,5-c]quinazolines and thiazolo[3 3 2,3][l,2,4]triazolo[l,5-fl]pyridines. 

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