New application of heterocyclic diazonium salts. Synthesis of pyrazolo[3,4-d][1,2,3]triazin-4-ones and imidazo[4,5-d][1,2,3]triazin-4-ones

Thermal Ring‐Opening of Pyrazolo[3,4‐d][1,2,3]triazin‐4‐ones: An Experimental and Theoretical Study

“…The structures of the 3 H ‐pyrazolotriazinone tautomers 4b – g were confirmed by NMR and IR spectroscopy, and the spectral data gave good agreement with those previously reported , , …”

“…The addition of triethylamine as base was required for the neutralization of the acid salts of the hydrazines. According to the results, in several cases, the application of microwaves improved the pyrazole yields in comparison with conventional synthesis; however, the main advantage was the significant reduction of the reaction times from hours to minutes (Table ) , . In particular, for the synthesis of 3b , the use of a mixture of water and ethanol as solvent led to an improved yield; it was found that the optimum ratio of water/ethanol was 1:3 (v/v).…”

“…Next, compounds 3a – g were subjected to diazotization conditions to prepare pyrazolo[3,4‐ d ][1,2,3]triazin‐4‐ones 4a – g using the protocol previously described (Scheme ) , . The yields of compounds 4 were good, with the exception of the pyridinyl derivative 4g and the 7‐unsubstituted pyrazolotriazinone 4a , the latter reaction proving totally unsuccessful (Table ).…”

“…The resulting solution was concentrated to dryness and the solid was recrystallized from ethanol, isolated by filtration, and washed with cold ethanol. The spectral data of compounds 3a – d , f correspond to literature data , , …”

“…In particular, azole‐annulated 1,2,3‐triazines possess activity as anti‐virals and anti‐tubercular agents, inhibitors of protoporphyrinogen oxidase, herbicides, and pesticides, among others . In view of the important biological activities of purine analogues, our research interests have been focused on the synthesis of pyrazolo[3,4‐ d ][1,2,3]triazin‐4‐ones and imidazo[4,5‐ d ][1,2,3]triazin‐4‐ones, establishing a convenient method to access a broad range of these derivatives through the one‐pot diazotization of 5‐aminoazole‐4‐carbonitrile precursors , . We found that the stability and transformations of the diazonium ion intermediate was strongly dependent on the type of azole ring and, to a lesser extent, the nature of the substituent at N‐1 …”