An Efficient, Green, Microwave-assisted Synthesis of Benzo[a]furo[2, 3-c]phenazine Derivatives with TiO2-SO3H as Cost-effective and Recyclable Catalyst under Solventfree Conditions

Background: A rapid, efficient, and environmentally benign procedure for the synthesis of novel furo [2,3-c]phenazine derivatives has been developed via reactions of 2-hydroxynaphthalene-1,4-dione, arylglyoxals, and indole in the presence of TiO2-SO3H-catalyst (TSAC) as a recyclable heterogeneous catalyst under solventfree conditions using microwave irradiation. Introduction: This study describes a successful approach for the synthesis of 2-(4-bromophenyl)-1-(1H-indol-3- yl) benzo[a]furo[2,3-c] phenazine in the presence of TiO2-SO3H-catalyst using microwave irradiation. Objectives: In this paper, we report an efficient and convenient method for the synthesis of phenazine derivatives from benzo[a]phenazin-5-ol, arylglyoxal derivatives, and indoles in the presence of TiO2-SO3H-catalyst under microwave irradiation. Materials and Methods: All reagents and solvents were purchased from Merck and Aldrich and used without further purification. 1H NMR spectra (DMSO) were recorded on the Gemini-500 MHz spectrophotometer with TMS as an internal standard. Results and Discussion: To investigate the reaction conditions for the synthesis of 2-(4-bromophenyl)-1-(1Hindol- 3-yl) benzo[a]furo [2, 3-c] phenazine derivatives, we performed a reaction between 2-hydroxynaphthalene- 1,4-dione (1 mmol) and aromatic 1,2-diamines (1 mmol) as a model. Conclusion: We demonstrated a green and straightforward procedure for the efficient synthesis of novel benzo[ a]furo[2, 3-c] phenazine derivatives in high yields via a one-pot, four-component domino protocol by using TiO2-SO3H as a mild, effective, non-toxic, and inexpensive solid acid catalyst without the addition of an organic co-solvent.