SYNTHESIS, REACTIONS AND THEORETICAL-STUDIES OF [1,2,4]TRIAZOLO[4,3-C]PYRIMIDINIUM-3-AMINIDE AND [1,2,4]TRIAZOLO[4,3-A]PYRAZINIUM-3-AMINIDE

[1,2,4]Triazolo[4,3-c]pyrimidinium-3-aminides 5a-h have been synthesis ed by treating pyrimidin-6-yl thiosemicarbazide derivatives 7f-n with dicyclohexylcarbodiimide (DCC), The above aminides 5a-h were slowly hy drolysed in water but very rapidly hydrolysed in 5 M aqueous hydrochlo ric acid to give substituted 1,2,4-triazole derivatives (e.g. 5a,d,g - -> 8e,a,f, respectively); related nucleophilic ring-opening reactions occurred when the aminides (cf. 5a-h) were treated with (separately) m ethanol and ethanol (e.g. 5d --> 8e and 8d, respectively), A series of analogous [1,2,4]triazolo[4,3-a]pyrazinium-3-aminides 6a-e was prepar ed following the procedures described above, The pyrazinium aminides 6 are stable in aq, 2 M HCl, and a stable hydrochloride salt 13 was for med from one such substrate 6a. The structure and electronic propertie s of condensed triazolium betaines 1, 5d, 6a and 15 have been studied using the semi-empirical PM3/COSMO method and with the ab initio 6-31 basis set; the implications of these results in respect of the potenti al of such betaines for molecular rearrangement are discussed.