A Regioselective Approach to Trisubstituted Pyrazoles via Palladium-Catalyzed Oxidative Sonogashira-Carbonylation of Arylhydrazines.

A palladium-catalyzed oxidative carbonylation of arylhydrazines and alkynes with balloon pressure CO/O to afford trisubstituted pyrazoles in a one-pot manner has been developed. The formation of trisubstituted pyrazoles involves a sequential C-N bond cleavage, carbonylation, Sonogashira coupling, Michael addition, and intramolecular condensation cyclization tandem process. An unprecedented oxidative Sonogashira-carbonylation reaction of arylhydrazine plays a key role for such a facile approach to pyrazoles.

Palladium-Catalyzed Oxidative Carbonylation of Aryl Hydrazines with CO and O at Atmospheric Pressure.

Palladium-catalyzed aerobic oxidative aminocarbonylation and alkoxycarbonylation reactions with aryl hydrazines as coupling partners have been developed. The oxidative carbonylation of aryl hydrazines proceeded smoothly at atmospheric pressure CO, employing molecular oxygen as the terminal oxidant. The only byproducts were nitrogen gas and water for both reactions.