Convergent synthesis of coumarin C3–C4-fused fluorogenic quinoline scaffolds via aldehyde activation using in situ generated hydrazoic acid

Herein, we report an efficient route for the construction of diversely substituted coumarin C3–C4-fused quinoline from pre-functionalized 4-azido-3-formylcoumarin using various aromatic/heterocyclic amines in excellent yield with a focus on application-oriented substrate scope. This protocol provides straightforward synthesis of fluorogenic coumarin-fused quinoline scaffolds through aldehyde activation using in situ generated HN₃ with excellent atom economy and without any secondary product formation.