Abstract A series of pyrazolo[1,5‐ a ]pyrimidin‐3‐ones 3 was prepared from Meldrum's acid and 5‐amino‐3‐arylpyrazoles 1 by cyclization in nitrobenzene of the corresponding 5‐pyrazolylaminomethylene Meldrum's acid derivatives 2 . The structure of pyrazolo[1,5‐ a ]pyrimidin‐3‐ones and their precursors were determined by nmr measurements.