A Flexible Synthetic Approach to Fluorescent Chromeno[4,3-b]pyridines and Pyrano[3,2-c]chromenes from Electron-Deficient 3-Vinylchromones.

We report a flexible approach to the synthesis of phenanthrene‐like heterocycles through organocatalytic ANRORC (Addition of the Nucleophile, Ring Opening, and Ring Closure) reaction of electron‐deficient 3‐vinylchromones with cyanoacetamide. Addition of highly basic DBU (1,8‐diazabicyclo[5.4.0]undec‐7‐ene) or tetramethylguanidine (TMG) at 80 °C leads to chromeno[4,3‐b]pyridines in good yields, whereas Et₃N at 20 °C made it possible to obtain the less accessible pyrano[3,2‐c]chromenes and their 2‐imines. The synthesis proceeds in mild conditions (EtOH, 20–80 °C), is versatile and applicable for a wide scope of reactants. The obtained compounds show bright fluorescence in the range 460–595 nm with high quantum yields (up to 0.84) in various solvents (MeCN, DMSO, EtOH, H₂O).