A facile and efficient one-pot three-step approach to the synthesis of substituted 1H- pyrazolo(4,3-d)pyrimidin-7(6H)-ones 4 from ethyl 3-cyano-1-(p-tolyl)-4-((triphenylphosphoran- ylidene)amino)-1H-pyrazole-5-carboxylate 1 has been developed. In this method, treatment of phospazene 1 with arylisocyanates and followed by nucleophilic addition with phenols/alcohols in the presence of a catalytic amount of K2CO3/R 2 ONa in THF at room temperature gave the corresponding 6-aryl-7-oxo-5-aryoxy/alkoxy-1-(p-tolyl)-6,7-dihydro-1H-pyrazolo(4,3-d)- pyrimidine-3-carbonitrile 4 in satisfactory to good yields.