A green, rapid, and efficient methodology is developed for the synthesis of 1‐phenyl‐3,5‐pyrazolidinedione (3) by the reaction of malonic acid with phenyl hydrazine in the presence of phosphorous oxychloride under solvent‐free conditions. The later compound 3 was used as a versatile precursor for green synthesis of chalcone derivatives (4a‐h) and spiroheterocyclic compounds (5a‐h) with good to excellent isolated yields. The chemical structures of the synthesized compounds were elucidated on the basis of elemental and spectral analyses.