One-pot synthesis using azo coupling: metal- and protecting-group-free synthesis of 5-hydroxy 2<i>H</i>-indazoles and 6-hydroxy cinnolin-3(2<i>H</i>)-ones

Abstract Azo coupling is a well-known method for the synthesis of azobenzenes; however, a one-pot protocol that uses this reaction has rarely been investigated due to its unique reaction conditions and azobenzene stability. Herein, we report a one-pot azo coupling/SOCl2-mediated intramolecular cyclization protocol that uses 3-hydroxybenzyl alcohols and diazonium salts to afford 5-hydroxy 2H-indazoles in yields of up to 82%. This process does not require transition metal catalysts, harsh conditions, long reaction times, or hydroxy group protection. 6-Hydroxy cinnolin-3(2H)-ones were also prepared using this one-pot system.