Synthesis of Unsymmetric Diaryl All-Carbon Quaternary Pyrazolones from Hydroxyphenyl Indolinones and Hydrazones.

The synthesis of unsymmetrical C4-diaryl all-carbon quaternary pyrazolones remains a significant challenge. Existing methods typically afford symmetric derivatives, which severely limit structural diversity. We report here the first construction of pyrazolones bearing an unsymmetric C4-diaryl all-carbon quaternary center through a one-pot cascade Michael addition/intramolecular ring-opening reaction of hydroxyphenyl indolinones with hydrazones. This approach features a broad substrate scope, excellent functional group tolerance, and mild reaction conditions. Density functional theory (DFT) calculations were performed to clarify the plausible reaction pathways governing the formation of unsymmetric C4-diaryl all-carbon quaternary pyrazolones, providing novel mechanistic insights into this transformation.