Reaction of 4-acetylpyridine (I) with hot dimethylformamide dimethyl acetal (II) gives the enamino ketone (III), which is then condensed with (3-amino-1H-pyrazol-4-yl)(2-pyridyl)methanone (IV) in boiling acetic acid. Intermediate (IV), (3-amino-1H-pyrazol-4-yl)(2-pyrid-yl)methanone, is obtained by condensation of 3-oxo-3-(2-pyridyl)propionitrile (V) with dimethylformamide dimethyl acetal (II) to provide 2-(dimethylaminomethylene)-3-oxo-3-(2-pyridyl)propionitrile (VI), which is finally coupled with aminoguanidine nitrate (VII) by means of 10N NaOH in refluxing EtOH
The enamino nitrile (IV) can be obtained by condensation of 3-oxo-3-(2-thienyl)propionitrile (VII) with dimethylformamide dimethylacetal in chloroform.
3-(Acetamido)acetophenone (VII) was converted to enaminone (VIII) upon condensation with dimethylformamide dimethylacetal. The amide N of (VIII) was then alkylated by means of iodomethane and NaH or, alternatively, under phase-transfer conditions to give (IX). Finally, condensation between enaminone (IX) and aminopyrazole (VI) in refluxing AcOH provided the target pyrazolopyrimidine.