Abstract
We describe the synthesis of so far synthetically not accessible 3,6-substituted-4,6-dihydro-3H-pyrazolo[3,4-d][1,2,3]triazines as nitrogen-rich heterocycles. The target compounds were obtained in five steps, including an amidation and a cyclative cleavage reaction as key reaction steps. The introduction of two side chains allowed a variation of the pyrazolo[3,4-d][1,2,3]triazine core with commercially available building blocks, enabling the extension of the protocol to gain other derivatives straightforwardly. Attempts to synthesize 3,7-substituted-4,7-dihydro-3H-pyrazolo[3,4-d][1,2,3]triazines, the regioisomers of the successfully gained 3,6-substituted 4,6-dihydro-3H-pyrazolo[3,4-d][1,2,3]triazines, were not successful under similar conditions due to the higher stability of the triazene functionality in the regioisomeric precursors and thus, the failure of the removal of the protective group.
Highlights
The structural motif of pyrazolotriazines, the pyrazolotriazinones, has drawn attention regarding a possible application as therapeutic agents due to manifold biological activities
We describe the synthesis of so far synthetically not accessible 3,6-substituted-4,6-dihydro-3H-pyrazolo[3,4-d][1,2,3]triazines as nitrogen-rich heterocycles
Several possibilities have been reported to gain the scaffold of pyrazolo[3,4-d][1,2,3]triazines synthetically and successful syntheses of different manifold isomers. 3,6-Dihydro-4Hpyrazolo[3,4-d][1,2,3]triazin-4-ones 2, as one example of the diverse compound class, can be gained via diazotization of 3-amino-1H-pyrazole-4-carboxamides 1a or 3-amino-1H-pyrazole-4-carbonitriles 1b and subsequent cyclization of the intermediate diazo compounds under acidic conditions [22] (Scheme 1)
Summary
The structural motif of pyrazolotriazines, the pyrazolotriazinones, has drawn attention regarding a possible application as therapeutic agents due to manifold biological activities. Several possibilities have been reported to gain the scaffold of pyrazolo[3,4-d][1,2,3]triazines synthetically and successful syntheses of different manifold isomers. 3,6-Dihydro-4Hpyrazolo[3,4-d][1,2,3]triazin-4-ones 2, as one example of the diverse compound class, can be gained via diazotization of 3-amino-1H-pyrazole-4-carboxamides 1a or 3-amino-1H-pyrazole-4-carbonitriles 1b and subsequent cyclization of the intermediate diazo compounds under acidic conditions [22] (Scheme 1).
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