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 regio-isomers of the successfully gained 3,6-substituted-4,6-dihydro-3H-pyrazolo[3,4-d][1,2,3]-3H-triazines, were not successful under similar conditions due to the higher stability of the triazene functionality in the regio-isomeric precursors and thus the failure of the removal of the protective group.
Keywords: Triazenes; Triazines; Pyrazoles; Diazonium chemistry; Cyclization
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Wippert, N.; Nieger, M.; Herlan, C.; Jung, N.; Bräse, S. Beilstein Arch. 2021, 202151. doi:10.3762/bxiv.2021.51.v1
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