Differentiation between [1,2,4]triazolo[1,5-a]pyrimidine and [1,2,4]triazolo[4,3-a]pyrimidine regioisomers by 1H-15N HMBC experiments

precursor was studied. In agreement with previous reports, two different bicycles, namely, bearing the regioisomeric [1,2,4]triazolo[1,5-a]pyrimidine (1) or(1,2,4) triazolo [4,3-a]pyrimidine (2) structural surrogates, could be obtained. We found that, depending on the triazole precursor, only one regioisomer resulted, either of the 1 or 2 series. We also observed that these two structural surrogates could be unambiguously differentiated by indirectly measuring their N-15 chemical shifts by H-1-N-15 HMBC experiments. The occasional conversion of [1,2,4]triazolo[4,3-a]pyrimidines to the [1,2,4]triazolo[1,5-a]pyrimidine counterparts could be unequivocally determined by N-15 NMR data. Copyright (C) 2010 John Wiley & Sons, Ltd.