4H‐pyrido[1,2‐a]pyrimidin‐4‐one and their derivatives are highly bioactive and multipurpose heterocyclic motifs, having application in drugs, natural products, agrochemical, material science, and organic synthesis. The C‐H functionalization of basic core structure of heterocycles have become indispensable tools that have continually increased the importance in the pharmaceutical industry for the synthesis of various useful heterocyclic molecules and their derivatives. In this review, we have provided a summary of various routes to synthesize 4H‐pyrido[1,2‐a]pyrimidin‐4‐one derivatives along with various derivatization methods such as via cross‐coupling, C‐H functionalization through arylation, alkenylation, sulfenylation, selenylation, phosphonation etc. taking into account the synthetic potentiality and significant influence of this scaffold in drug discovery.

A lenient approach for regioselective C3−H chalcogenation and thiocyanation of 4H‐pyrido[1,2‐a] pyrimidin‐4‐ones is developed using visible light photocatalysis. This operationally straightforward method furnishes a broad array of C‐3, Ar−S/Ar−Se and ‐SCN functionalized derivatives in moderate to high yields. This protocol employs visible light as an environmentally friendly energy source, cost effective inorganic persulfate‐based oxidant and easily procurable dichalcogenides for regioselective C−H chalcogenation of the substrate at room temperature. Further, regioselective thiocyanation of 4H‐pyrido[1,2‐a] pyrimidin‐4‐ones was also developed. Mechanistic path for these transformations has been proposed based on light on/off and Stern‐Volmer studies as well as quantum yield calculations.