Catalyst-free synthesis of chromeno-furo-pyridinones via intramolecular [4 + 2] cycloaddition.

A step-economical, catalyst-free intramolecular Diels-Alder strategy has been developed for the synthesis of previously unexplored polycyclic chromeno-furo-pyridinones. The transformation proceeds via in situ imine formation, followed by a thermally driven [4 + 2]-cycloaddition with the tethered alkyne and subsequent aromatization, in a single operational step. This cascade process constructs two heterocyclic rings and three new bonds (two C-C bonds and one C-N bond), with water as the sole stoichiometric byproduct. This protocol features a broad substrate scope, high functional group tolerance, and excellent step economy, furnishing diverse functionalized chromeno-furo-pyridinones in good to excellent yields. The resulting polycyclic scaffolds represent versatile synthetic intermediates for further derivatization, providing access to structurally complex and molecularly diverse heterocyclic architectures.