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.
By condensation of 2,4-dichlorobenzoic acid (I) with anthranilic acid (II) by means of K2CO3, powdered Cu and a small amount of I2 in refluxing isoamyl alcohol.
Condensation of 2-acetylthiophene (I) with dimethylformamide dimethylacetal produced enaminone (II), which was subsequently cyclized to the isoxazole (III) upon treatment with hydroxylamine. Further condensation of (III) with dimethylformamide dimethylacetal, with concomitant isoxazole ring opening, gave rise to the enamino nitrile (IV). This was then cyclized with aminoguanidine nitrate (V) under basic conditions to furnish the intermediate aminopyrazole (VI).
Bromination of 5-aminopyrazole (XI) with Br2 in AcOH gives 4-bromo-5-aminopyrazole (XII), which is cyclized with N-[3-[3-(dimethylamino)-2-propenoyl]phen-yl]-N-methylacetamide (X) in AcOH to yield the 3-bromo-pyrazolo[1,5-a]pyrimidine derivative (XIII). Finally, this compound can be condensed with either 2-thienylcarbonyl chloride (XIV) by means of Zn or Mg or with 2-thienylboronic acid (XV) and CO by means of a Pd(0) catalyst.
Cyclization of 2-aminopyrazole (XI) with the acetamide (X) in AcOH gives the pyrazolo[1,5-a]pyrimidine derivative (XVI), which is finally acylated with 2-thienylcarbonyl chloride (XIV) by means of AlCl3.
Cyclization of ethoxymethylenemalonodinitrile (XVII) with hydrazine gives 5-aminopyrazole-4-carbonitrile (XVIII), which is further cyclized with acetamide (X) in refluxing AcOH to yield the 3-cyanopyrazolo[1,5-a]pyrimidine derivative (XIX). Finally, this compound is condensed with 2-bromothiophene (XX) by means of Mg.
Cyclization of 5-aminopyrazole-4-carboxylic acid ethyl ester (XXI) with either, 3,3-diethoxypropionic acid ethyl ester (XXII) or 3-oxopropionic acid ethyl ester (XXIII) in refluxing AcOH gives 7-hydroxypyrazolo[1,5-a]pyrimidine-3-carboxylic acid ethyl ester (XXIV), which is treated with POCl3 to yield the corresponding chloro derivative (XXV). Condensation of compound (XXV) with 3-(N-methylacetamido)phenylboronic acid (XXVI) by means of Pd(PPh3)4 and Na2CO3 in ethanol affords the pyrazolo-[1,5-a]pyrimidine-carboxylic acid ethyl ester (XXVII), which is finally condensed with 2-bromothiophene (XX) and Mg.
Reaction of 3-(acetamido)acetophenone (VIII) with iodomethane and NaH gives 3-(N-methylacetamido)acetophenone (XXVIII), which is mixed with 3-oxo-3-(2-thienyl)propionitrile (VII) and treated with dimethylformamide dimethylacetal to yield a mixture of the dimethylaminomethylene derivatives (IV) and (X). This mixture, without isolation, is cyclized with aminoguanidine (V) by treatment first with NaOH in ethanol and then with refluxing AcOH.