A New Family of Fused Azolo[1,5-a]pteridines and Azolo[5,1-b]purines

[Image: see text] The nitration of azolo[1,5-a]pyrimidin-7-amines with several nitration agents (such as acetic nitric anhydride, nitronium tetrafluoroborate, and a mixture of concentrated nitric acid and sulfuric acid) has been investigated. It has been shown that, depending on the conditions, the nitration of pyrazolopyrimidin-7-amines bearing electron-withdrawing groups in the pyrazole ring leads to nitration products in the pyrimidine and/or pyrazole ring. The nitration of triazolo[1,5-a]pyrimidin-7-amines with “nitrating mixture” has been optimized, thus allowing us to obtain a series of 6-nitro[1,2,4]triazolo[1,5-a]pyrimidin-7-amines, followed by their reduction into the corresponding [1,2,4]triazolo[1,5-a]pyrimidin-6,7-diamines (yields 86–89%). The latter have been subjected to heterocyclization by a variety of electrophilic compounds (such as CS(2), glyoxal, triethyl orthoformate) with the formation of five- or six-membered annulated cycles.