Intramolecular oxidative C–N bond formation under metal-free conditions: One-pot global functionalization of pyrazole ring

Herein, we report an efficient DTBP promoted and NaI-catalyzed, greener protocol for the synthesis of highly substituted pyrazoles via C(sp2)–H bond functionalization. This protocol is general and the reaction efficacy improves significantly with the combined use of solvents t-BuOH and EtOH, producing a vast variety of substituted pyrazoles in good to excellent yields. The mechanistic investigations including the radical trapping experiment indicating the in-situ generation of intermediate free-radical species followed by intramolecular oxidative C–N bond formation afforded the desired pyrazole moiety. The synthetic versatility of this methodology is further highlighted by preparing a diverse range of substrates including di-/tri-/and tetra-substituted pyrazoles, and applying the methodology in the practical synthesis of bioactive scaffolds.