3-Oxo-2-arylhydrazononitriles 1a-c react readily with chloroacetonitrile, ethyl chloroacetate, and with phenacyl chloride to give 4-aminopyrazoles 4a-e. The pyrazolo[4,3-d]pyrimidine derivatives 7 and 10 are synthesized via reaction of the aminopyrazole 4b with phenylisothiocyanate and DMFDMA/NH4OAc respectively.
Ghozlan, S. A. S., Badahdah, K. O., & Abdelhamid, I. A. (2007). An easy synthesis of 5-functionally substituted ethyl 4-amino-l-aryl- Pyrazolo-3-carboxylates: Interesting precursors to sildenafil analogues. Beilstein Journal of Organic Chemistry, 3. https://doi.org/10.1186/1860-5397-3-15