Synthesis of Pyrazolo[1,2‐a]cinnolines via Rhodium(III)‐Catalyzed [4+2] Annulation Reactions of Pyrazolidinones with Sulfoxonium Ylides

Abstract A method to synthesize pyrazolo[1,2‐a]cinnolines via rhodium(III)‐catalyzed C−H activation of pyrazolidinones and subsequent [4+2] annulation of sulfoxonium ylides was developed. 5‐Substituted or 5,10‐disubstituted pyrazolo[1,2‐a]cinnolines could be obtained by slightly adjusting the reaction conditions. Gram‐scale synthesis and practical transformations proved the practicability of this method. The mechanism of this method was proposed in the article on the basis of preliminary mechanistic results and previous reports. This method features simplified operation, metal‐oxidant free, and readily available reactants. magnified image