3‐Diazopyrazolo[3,4‐b] pyridine, a versatile synthon for new heterocyclic systems

Abstract 3‐Diazopyrazolo[3,4‐b] pyridine was synthesized and its transformations were investigated. With reactive methylene compounds the corresponding hydrazones are formed and they can be cyclized into condensed 1,2,4‐triazine derivatives. With amines of thiols the diazo compound forms triazenes or diazosulfides. From hydrazines tetrazenes are formed first and they give upon fragmentation a mixture of N‐N or C‐N bond fission products. The diazo compound undergoes cycloaddition, reacting as a 1,2‐dipole. 3‐Azidopyrazolo [3,4‐b] pyridine was prepared and converted into the tetrazolo isomer, whereas the 3‐amino compound was used for the synthesis of some pyridopyrazolopyrimidines.