“…Four different possibilities exist for the relative orientation of both rings, so four different isomeric families of compounds are defined: 1,2,4-triazolo [1,5- Among these isomeric families of compounds, 1,2,4-triazolo[1,5-a]-pyrimidine derivatives are thermodynamically more stable and, thus, the most studied ones [15], a few of them being commercially available. Revisions surveying the synthesis, reactivity, spectroscopic characterization and crystallographic studies of 1,2,4-triazolo [1,5-c]-pyrimidines [16], 1,2,4-triazolo [4,3-a]pyrimidines [17] and 1,2,4-triazolo [4,3-c]pyrimidines [18] have also been published.…”