The chemistry of polyazaheterocyclic compounds. Part V. The synthesis and reactivity of the v-triazolo[3,4-a]pyrimidine ring system

Abstract

Heating the 4-substituted 5-amino-1H-1,2,3-triazoles (7a and b) and acetylacetone with piperidine in ethanol affords the v-triazolo[3,4-a]pyrimidine derivatives (9a and b) in high yield. Scission of the triazole ring in the triazolopyrimidine (9a) occurs in hot glacial acetic acid alone or in the presence of acetyl chloride, or in trifluoro-acetic acid, yielding the 2-substituted pyrimidine derivatives (13a), (13c), and (13e), respectively. Condensation of the aminotriazole (7a) with acetylacetone in glacial acetic acid is accompanied by scission of the triazole ring to give the acetoxybenzylpyrimidine (13a). In contrast, heating the amide (7b) with acetylacetone in glacial acetic acid yields the v-triazolopyrimidine derivative (9b), which is stable to prolonged treatment with acetic or trifluoroacetic acid. The synthesis and scission of other v-triazolo[3,4-a]pyrimidine derivatives are described.