Tricyclic heteroaromatic systems containing a bridgehead nitrogen atom. Part 3. [1,2,4]Triazolo[3′,4′ : 3,2]pyrazolo[3,4-d]pyrimidines, tetrazolo[1′,5′ : 1,5]pyrazolo[3,4-d]pyrimidines and pyrimido-[5′,4′ : 4,5]pyrazolo[3,2-c][1,2,4]triazines

Abstract

6-Phenyl-1H-pyrazolo[3,4-d]pyrimidin-3(2H)-one 16 has been prepared and converted into its 3-chloro 6, 3-thioxo 17 and 3-methylthio derivatives 9. Each of these could be converted into the 3-hydrazino derivative 3, cyclisation of which with carbon disulfide or triethyl orthoformate generated the fused 1,2,4-triazoles 23 and 20, respectively. Alternatively, the hydrazino derivative 3 gave a substituted hydrazide 26 or thiosemicarbazide 25, from which the 1,2,4-triazoles 21 and 22 respectively were obtained. The equilibrium between 3-azido-6-phenyl-1H-pyrazolo[3,4-d]-pyrimidine 5 and 2-phenyl-9H-tetrazolo[1′5′ : 1,5]pyrazolo[3,4-d]pyrimidine 27 was studied.

3-Diazo-4-methyl-6-phenyl-1H-pyrazolo[3,4-d]pyrimidine 29 was prepared by diazotisation of the corresponding amine 1 and converted into the 3-azido compound 4, which could not be cyclised to form a tetrazole. Finally, the diazo compound 29 readily formed the pyrimido[5′4′ : 4,5]pyrazolo-[3,2-c][1,2,4]triazine derivatives 32 and 33, when treated with pentane-2,4-dione and ethyl acetoacetate respectively.