C(sp<sup>3</sup>)–H Carbonylative Cyclization\nof Hydrazones with CO<sub>2</sub>: Synthesis of Pyrazolone Derivatives

A novel method is reported to synthesize various pyrazolones\nthrough\ntransition-metal-free and redox-neutral 1°, 2°, or 3°\nC(sp<sup>3</sup>)–H carbonylative cyclization using 1 atm of\nCO<sub>2</sub> as a green carbonyl source, featuring good functional\ngroup tolerance, a broad substrate scope, facile scalability, and\neasy product transformation. The utility of this method could be demonstrated\nby the applications in preparing useful synthetic intermediates and\nbioactive compounds.