L-proline/urea catalyzed,novel, and eco-friendly synthesis of coumarin substituted-3-indoloxanthenes

A green and eco-friendly synthesis of coumarin substituted-3-indoloxanthenes 4(a-l) has been developed using urea/L-proline as simple catalyst. Two efficient methods have been described for the synthesis of these 3-indoloxanthene derivatives. In the first method, Knoevenagel condensation, then Pinner cyclisation followed by 1,4 addition between 4-hydroxy-1-methyl-2-oxo-1,2-dihydrocoumarin-3-carbaldehyde 1(a-b) , with cyclohexane-1,3-dione (2) and indole 3(a-f) using of L-proline as catalyst was described. In the second method, urea/thiourea catalyzes the same reaction at 100°C for 10 minutes to afford the title compounds 4(a-l) . These two protocols involve eco-friendly and inexpensive catalysts, give excellent yields of the clean products without the need of column chromatography for their isolation or purification.