Synthesis and antibacterial activity of new oxadiazolo[1,3,5]-triazine, 1,2,4 triazolo and thiadiazolo 1,3,4 oxadiazole derivatives

Abstract

3-Formyl-4-hydroxycoumarin has been treated with semicarbazide to give 4-hydroxy-2-oxo-2<i>H</i>[1]-benzopyran-3-aldehyde semicarbazone <b>1a-d</b>, which on oxidative cyclization with bromine in glacial acetic acid in the presence of anhydrous sodium acetate gives 3-(5-amino-1,3,4-oxadiazol-2-yl)-4-hydroxy-2<i>H</i>[1]-benzopyran-2-one <b>2a-d</b>.<b> </b>3-(5-amino-1,3,4-oxadiazol-2-yl)-4-hydroxy-2<i>H</i>[1]-benzopyran-2-one on reaction with benzaldehyde gives 4-hydroxy-3-(5-benzylidine imino 1,3,4-oxadiazol-2-yl)-2<i>H</i>[1]-benzopyran-2-one <b>3a-d</b>.<b> 3a-d </b>on (4+2) cycloaddition with phenyl isothiocynate gives 3-(6,7-diphenyl-5-thioxo-6,7-dihydro-5<i>H</i>-[1,3,4]oxadiazolo[3,2-<i><img src='/image/spc_char/alpha.gif' border=0></i>][1,3,5]triazin-2-yl)-4-hydroxy-2<i>H</i>[1]-benzopyran-2-one <b>4a-d</b>.<b> 2a-d</b> undergoes regioselective condensation with KSCN in methanol to give N-[5-(4-hydroxy-2-oxo-2<i>H</i>[1]-benzopyran-3-yl)-1,3,4,-oxadiazol-2-yl]thiourea<b> 5a-d</b> whereas with phenyl isothiocynate it gives N-[5-(-4-hydroxy-2-oxo-2<i>H</i>[1]benzopyran-3-yl)-1,3,4-oxadiazole-2-yl]-N'-phenylthiourea <b>7a-d</b>. <b>5a-d</b> reacts with thionyl chloride in pyridine to give 4-hydroxy-3-(6-thioxo-5,6-dihydro[1,2,4]triazolo[5,1-<i>b</i>][1,3,4]oxadiazol-2-yl)-2<i>H</i>[1]-benzopyran-2-one <b>6a-d</b>.<b> 7a-d</b> on treatment with ethanol and iodine yields 4-hydroxy-3-[6-phenylimino-6<i>H</i>-[1,2,4]-thiadiazolo[3,2-<i>b</i>][1,3,4]-oxadiazol-2-yl]-2<i>H</i>[1]benzopyran-2-one<b> 8a-d</b>.