CO₂-Driven C(sp²)-H Lactamization to 2-Quinolinones

2-Quinolinones are key scaffolds in pharmaceuticals, yet their synthesis under mild and sustainable conditions remains challenging. We report a transition-metal-free C(sp²)-H lactamization of azido-alkenes using CO₂ as a one-carbon source. The reaction proceeds under mild conditions with dimethyl phenylphosphonite, affording 2-quinolinones with excellent functional-group tolerance. The method enables ¹³C-labeling with 99% incorporation, gram-scale synthesis, and downstream functionalizations, providing access to biologically relevant molecules. This strategy provides a versatile alternative to conventional and metal-catalyzed quinolinone syntheses.