Pd-Catalyzed Ag(I)-Promoted C3-Arylation of Pyrido[1,2-a]pyrimidin-4-ones with Bromo/Iodo-Arenes.

A regioselective Ag(I)-promoted Pd-catalyzed C3-H activation-arylation of pyrido[1,2-a]pyrimidin-4-ones with bromo/iodo-(hetero)arenes under aqueous conditions has been developed. It affords an efficient access to pharmaceutically important versatile 3-aryl-pyrido[1,2-a]pyrimidin-4-ones. Interestingly, the arylation undergoes via a pathway with an unusual feature involving the formation of cationic arylpalladium species promoted by halo-sequestering Ag salts enabling concerted C3-palladation-deprotonation, as explored by relevant experiments and spectroscopic studies. The present approach is step economical, good yielding, and compatible with various functionalities and applicable to a wide range of starting materials.