Regiospecific synthesis of 6-aryl-3-cyano-5-alkylamino/arylamino-1-p-tolyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-ones via iminophosphorane-mediated annulation

An efficient and straightforward approach to the synthesis of 6-aryl-3-cyano-5-alkylamino-1-p-tolyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-ones 8 has been developed from the readily commercially available starting materials 4-methylaniline and malononitrile in five steps. The key to the pyrazolo[4, 3-d]pyrimidin-7(6H)-ones relies on an iminophosphorane-mediated annulation, followed by a nucleophilic addition with amines. The structures of the title compounds are clearly characterized by IR, 1H NMR, MS, elemental analysis or X-ray diffraction crystallography.