5-Oxo and 7-oxo derivatives of [1,2,4]triazolo-[1,5-a]pyrimidine: characterization and theoretical study

4,5-Dihydro-5-oxo-[ 1,2,4]triazolo-[1,5-a]pyrimidine (5HtpO) and 4,7-dihydr o-7-oxo-[1,2,4]triazolo-[1,5-a]pyrimidine (7HtpO) have been synthesized by the condensation of 3-amino-[1,2,4]triazole with a reagent bearing the thre e carbon atoms that close the six-membered ring in a strongly acidic (7HtpO ) or strongly basic (5HtpO) medium. The crystal structures of these compoun ds have been determined by X-ray diffraction, exhibiting the N4-H tautomer, as expected from the RHF/AM1 calculations. The different possibilities for binding metal ions are discussed from the MO results. (C) 2000 Elsevier Sc ience B.V. All rights reserved.