In an alternative method, chlorination of pyrazole-3,4-dicarboxylic acid (I) with SOCl2 produces acid chloride (II), which is further converted into diamide (III) upon treatment with ammonia. Subsequent Hofmann rearrangement of amide (III) in the presence of sodium hypochlorite leads to the target pyrazolopyrimidine compound (3, 4).

1) The esterification of 1-(4-chlorobenzoyl)-3-(4-phenyl-1-piperazinyl)propanol (I) with phosgene by means of triethylamine in CHCl3 gives the corresponding chloroformate ester (II), which is then cyclized by heating.

2) By direct cyclization of (I) with N,N'- carbonyldiimidazole (III) in refluxing benzene.

3) By direct cyclization of (I) with phosgene in refluxing CHCl3.

Cyanoacetic acid (I) is condensed with urethane (II) in hot Ac2O to afford N ethoxycarbonyl-cyanoacetamide (III). Subsequent reaction of (III) with triethyl orthoformate yields alpha-cyano-beta-ethoxy-N-ethoxycarbonyl-acrylamide (IV). The ethoxy group of (IV) is then displaced with hydrazine hydrate in EtOH to produce the hydrazino acrylamide (V). Finally, thermal cyclization of (V) gives rise to the title pyrazolopyrimidine (1, 2).

In an alternative method, chlorination of pyrazole-3,4-dicarboxylic acid (I) with SOCl2 produces acid chloride (II), which is further converted into diamide (III) upon treatment with ammonia. Subsequent Hofmann rearrangement of amide (III) in the presence of sodium hypochlorite leads to the target pyrazolopyrimidine compound (3, 4).

Cyanoacetic acid (I) is condensed with urethane (II) in hot Ac2O to afford N ethoxycarbonyl-cyanoacetamide (III). Subsequent reaction of (III) with triethyl orthoformate yields alpha-cyano-beta-ethoxy-N-ethoxycarbonyl-acrylamide (IV). The ethoxy group of (IV) is then displaced with hydrazine hydrate in EtOH to produce the hydrazino acrylamide (V). Finally, thermal cyclization of (V) gives rise to the title pyrazolopyrimidine (1, 2).