Copper‐Catalyzed C4‐selective Carboxylation of Pyridines with CO2 via Pyridylphosphonium Salts

Pyridine motifs are widespread pharmacophores in many drugs. Installing various substituents through pyridine C−H bond functionalization is significant for new drug design and discovery. Developments of late‐stage functionalization reactions enrich the strategies for selective functionalization of pyridines. However, late‐stage C−H carboxylation of pyridines is a long‐standing challenge, especially selectively carboxylation with CO2 on pyridine motifs. Herein, we describe a practical method for C4−H carboxylation of pyridines via one‐pot C−H phosphination and copper‐catalyzed carboxylation of the resulted phosphonium salts with CO2. The reaction is conducted under mild conditions and compatible with multiple active groups and several pyridine drugs, providing diverse valuable isonicotinic acid compounds, demonstrating the application potential of this strategy.