Synthesis and properties of iso viagra . A 2‐methyl‐2 H ‐pyrazolo[4,3‐ d ]pyrirnidin‐7‐one isomer of viagra ®

The synthesis and spectral properties (ir, ms, nmr) of a substituted 2‐methyl‐2 H ‐pyrazolo[4,3‐ d ]‐pyrimidin‐7‐one ( 3 ), an isomer of Viagra ® , are described. The key synthon, 4‐amino‐1‐methyl‐5‐propyl‐3‐pyrazolecarboxamide ( 7 ), is prepared via the reaction of ethyl 2,4‐dioxoheptanoate with methylhydrazine, followed by cyclization, nitration, amidation, and nitro group reduction. Interaction of 7 with 2‐ethoxyben‐zoyl chloride yielded the respective bis‐amide ( 8 ) which was cyclized in polyphosphoric acid to the corresponding pyrazolo[4,3‐ d ]pyrimidin‐7‐one derivative 9 . Chlorosulfonylation of 9 , and subsequent treatment with 1‐methylpiperazine furnished iso Viagra ( 3 ).