Catalytic Photoredox C-H Arylation of 4-Oxo-4 H -pyrido[1,2- a ]pyrimidine-3-diazonium Tetrafluoroborates and Related Heteroaryl Diazonium Salts.

Irradiation of mixtures of title diazonium salts and heteroarenes with green light (510 nm) in the presence of eosin Y disodium salt ( EY-Na 2 ) as a photocatalyst furnished the corresponding arylation products in 8-63% yields. The proposed photocatalytic cycle is analogous to that proposed previously for closely related photoredox C-H arylations with aryl diazonium salts as aryl radical sources. This method has a broad substrate scope and represents a metal-free alternative for the synthesis of 3-heteroaryl-substituted 4 H -quinolizin-4-ones and azino- and azolo-fused pyrimidones with a bridgehead nitrogen atom.