Synthesis of new 1-(3,4-dimethylphenyl)-1,5-dihydropyrazolo[3,4-<Emphasis Type="Italic">d</Emphasis>]pyrimidin-4-one derivatives

New substituted pyrazolo3,4-d]pyrimidin-4-ones have been synthesized as a result of a series of transformations including hydrolysis of ethyl 5-amino-1H-pyrazole-4-carboxylates, cyclization of the carboxylic acids thus obtained to pyrazolo3,4-d]1,3]oxazin-4(1H)-ones, and treatment of the latter with substituted anilines. The final pyrazolo3,4-d]pyrimidin-4-one derivatives can also be synthesized from 5-(arylamido)-1H-pyrazole-4-carboxylic acids in the presence of a catalytic amount of anhydrous zinc(II) chloride.