Chemoselective Access to π‐Conjugated Heterocycles by Stille and Sonogashira Reactions on 2‐Substituted 4H‐Pyrido[e][1,3]oxazin‐4‐ones

Site‐selective PdII‐catalyzed cross‐coupling reactions of 2‐substituted‐4H‐pyrido[e][1,3]oxazin‐4‐ones were developed. C4‐ and C5‐alkynylated pyridooxazinones were thus obtained through Sonogashira coupling, whereas the efficient incorporation of (hetero)aryl and ethenyl substituents at the C5 position was achieved by Stille coupling. Finally, an example of one‐pot sequential multiple Sonogashira reactions with different alkynes was realized. The strategy developed herein provides rapid access to polyfunctionalized precursors with extended π‐conjugation for further application as fluorescent materials.