Eco-friendly construction of highly functionalized chromenopyridinones by an organocatalyzed solid-state melt reaction and their optical properties
The library construction of highly functionalized and diverse chromenopyridinones was achieved by three-component reactions of various 4-hydroxycoumarins with ammonium acetate and 3-formylchromones under L-proline catalyzed solid-state melt conditions. The advantages of this protocol include the use of an inexpensive organocatalyst, avoidance of toxic organic solvents, environmentally benign conditions, an easy work-up procedure and good to excellent product yields. The optical properties of these π-expanded varieties of the synthesized chromenopyridinone derivatives were also examined. A chromeno[4,3-b]pyridine nucleus bearing an electron donating group exhibited strong emission in the blue-green region of the visible spectrum.