Used as a key intermediate in the synthesis of Sildenafil (Viagra) and related phosphodiesterase type 5 (PDE5) inhibitors. This sulfonyl chloride derivative enables the formation of the sulfonamide linkage essential for the drug's activity. Its structure facilitates targeted modifications in medicinal chemistry, making it valuable for developing therapies that promote vasodilation and improve blood flow in conditions such as erectile dysfunction and pulmonary arterial hypertension. Commonly utilized in pharmaceutical research laboratories to assemble complex pyrazolo[4,3-d]pyrimidine-based molecules with potent biological effects.