2,5‐Disubstituted Pyrazolo[4,3‐ c ]cinnolin‐3‐ones

Complementary strategies to 2,5‐disubstituted pyrazolo[4,3‐ c ]cinnolin‐3‐ones are reported herein, providing late stage substituent introduction at either the 2‐ or the 5‐position. Treating a readily prepared 4‐thiocinnoline ester with substituted hydrazines afforded late stage access to the 2‐position, while late stage substituent introduction at the 5‐position was achieved via two different strategies: alkylation of 4‐hydrazonopyrazol‐3‐ones, followed by a ring‐closing intramolecular S N Ar tactic and direct reaction of 5‐(2‐fluorophenyl)‐2,4‐dihydro‐3 H ‐pyrazol‐3‐ones with aryl diazonium salts, followed by cyclization . The strategies described herein provide practical and general methods to prepare 2,5‐disubstituted pyrazolo[4,3‐ c ]cinnolin‐3‐ones.