Rapid Construction of Indolo[1,2-a]quinoline Pyrazino[1,2-a]quinoline Scaffolds via Instant Condensation and Copper-Catalyzed C–H Activation

We report a modular and efficient two-step strategy for the construction of novel tetracyclic indolo[1,2-a]quinoline–pyrazino[1,2-a]quinoline frameworks. In the first step, 2-formylbenzoates condense instantly with 2-aminopyridine to furnish tricyclic dihydropyridopyrazino intermediates under mild, catalyst-free conditions. In the second step, these intermediates undergo copper(I)-catalyzed annulation with 2-pyridinecarboxaldehydes via C–H activation, affording structurally complex tetracyclic products. This protocol features a broad substrate scope, functional group tolerance, and mild conditions, highlighting its potential for medicinal chemistry applications.