Sequential Knoevenagel [4+1] Cycloaddition–Condensation–Aza-Friedel–Crafts Intramolecular Cyclization: A 4‑Center-3-Component Reaction Toward Tunable Fluorescent Indolizine Tetracycles

A two-step multicomponent reaction oxidation protocol is reported herein, which affords novel tunable fluorescent tetracyclic indolizines. The procedure involves a novel 4-center-3-component reaction, which proceeds via a sequential Knoevenagel condensation, [4+1] cycloaddition, and imine condensation to afford imino-indolizines. Products then undergo cyclization and are oxidized in situ to afford fluorescent tetracycles, which are readily tunable through modification of diversity elements.