Microwave‐assisted Domino Cyclization for the Synthesis of Novel Spiro‐benzo[a]phenazine Annulated Heterocycles Catalyzed by a Basic Ionic Liquid

An efficient and green strategy for the improved synthesis of a biologically and pharmaceutically interesting multi‐functionalized diverse novel spiro‐benzo[a]phenazine annulated heterocycles was developed with the assistance of microwave irradiation. A sequential one‐pot, two‐step domino reaction starting from 2‐hydroxynaphthalene‐1,4‐dione, benzene‐1,2‐diamines, a cyclic carbonyl compound, and 1,3‐indandione in the presence of a basic ionic liquid (1‐butyl‐3‐methylimidazolium hydroxide) as an expedient, ecofriendly and reusable catalyst afforded the corresponding novel spiro[benzo[a]indeno[2′,1′:5,6]pyrano[2,3‐c]phenazine] derivatives with high yield under solvent‐free conditions. This domino Knoevenagel–Michael annulation reaction provided five new bonds (two C–C, two CN, and one C–O) and two new rings through multiple operations in a single flask. We demonstrate a one‐pot, four‐component domino cyclization for the green synthesis of a biologically and pharmaceutically interesting kinds of multifunctionalized novel spiro[benzo[a]indeno[2′,1′:5,6]pyrano[2,3‐c]phenazine] derivatives in excellent yields and purities with very short reaction times, from readily available starting materials by using a basic ionic liquid [BMIM]OH as an environmentally benign catalyst, under microwave irradiation conditions.