Cobalt-catalyzed reductive carboxylation of pyridines with CO2via pyridylphosphonium salts

Abstract

Reports on late-stage C–H bond carboxylation reactions using CO₂ are very limited. In this work, a cobalt-catalyzed carboxylation reaction of pyridylphosphonium salts with CO₂ has been developed. The catalyst system consisting of Co(acac)₂ and Mn is convenient and practical. When combined with triphenylphosphonation of the C4–H bond of pyridines, the formal C4–H carboxylation of pyridines with CO₂ can be achieved via a one-pot, two-step procedure. This method has been further applied to the late-stage C–H bond carboxylation modifications of pyridine-containing drug molecules, such as loratadine.