Reaction of triethyl orthopropionate (I) with malononitrile (II) at reflux temperature provided (1-ethoxypropylidene)malononitrile (III). Cyclopentanone (IV) was condensed with tert-butyl carbazate (V) to afford the corresponding hydrazone (VI). Subsequent reduction with sodium cyanoborohydride, followed by acid deprotection furnished cyclopentylhydrazine (VII). Then, condensation of (VII) with malononitrile derivative (III) produced pyrazole (VIII). Partial hydrolysis of the cyano group of (VIII) using concentrated sulfuric acid gave carboxamide (IX).

Treatment of 4-cyanopyridine N-oxide (X) with phosphorus oxychloride and phosphorus pentachloride under reflux produced a mixture of 2-chloro (XI) and 3-chloropyridines (XII), which were separated by column chromatography. The 3-chloro isomer (XII) was further treated with sodium ethoxide in DMF to produce the ethoxypyridine (XIII). The pyrazolopyrimidine nucleus (XIV) was then obtained by condensation of cyanopyridine (XIII) with aminopyrazole (IX) in the presence of NaH. Finally, diazotization of (XIV) in 50% sulfuric acid converted the aminopyrimidine group into the required pyrimidinone.