Synthesis of 3-tert-Butyl-4-hydroxy-1,4-dihydropyrazolo[5,1-c][1,2,4]triazines

Two new approaches have been proposed for the synthesis of 4-hydroxy-1,4-dihydropyrazolo[5,1-c]-[1,2,4]triazines via (1) borohydride reduction of 1-R-4-oxo-1,4-dihydro derivatives and (2) Vilsmeier formylation of 3-tert-butyl-8-methylpyrazolo[5,1-c][1,2,4]triazine. 3-tert-Butylpyrazolo[5,1-c][1,2,4]triazin-1(5)-ium cation has been generated for the first time by treatment of 7-amino-1-benzyl-3-tert-butyl-4-hydroxy-1,4-dihydropyrazolo[5,1-c][1,2,4]triazine-8-carbonitrile with trifluoroacetic acid in CDCl3. The hydrolysis of 4-alkoxy-1,4-dihydropyrazolo[5,1-c][1,2,4]triazines was monitored by H-1 and C-13 NMR spectroscopy. The structure of the synthesized compounds was confirmed by spectral and X-ray diffraction data.