Bi Metal-Organic Framework (Ce/Ni-BTC) as Heterogeneous Catalyst for the Green Synthesis of Substituted Chromeno[4, 3-b]quinolone under Solvent Free Condition

Abstract

Aims: Novel bi metal organic framework (b-MOF) is synthesized and used as a heterogeneous catalyst for the synthesis of chromeno[4, 3-b]quinolone derivatives via one-pot and solvent-free, four-component reaction of dimedone, aromatic aldehydes, 4-hydroxycoumarin and ammonium acetate at 110°C.

Background: b-MOFs can be used as a heterogeneous catalyst in the synthesis of many organic compounds. The active and multi-purpose sites in b-MOFs provide a varied function in their catalytic applications. In this paper, reductive CES method is applied for the synthesis of Ce_0.47/Ni_0.53-BTC b-MOF. The resulting b-MOF was used as a heterogeneous catalyst for the synthesis of chromeno[4, 3-b]quinolone via one-pot and solvent-free, fourcomponent reaction of dimedone, aromatic aldehyde, 4-hydroxycoumarin and ammonium acetate at 110 °C.

Method: Ce_0.47/Ni_0.53-BTC was synthesized in an electrochemical cell composed of a stainless steel foil with a size of 5cm×5cm centered between two 5cm×5cm sized graphite plates as the anodes by the cathodic current density of 0.2 A/dm² and placed in a solution of cerium nitrate (0.3 g), nickel nitrate (0.3 g), H₃BTC (0.2 g) and NaNO₃ (0.1 g) in ethanol (500 mL). Ce_0.47/Ni_0.53-BTC (10 mg) was added to a mixture of dimedone (1 mmol), aromatic aldehyde (1 mmol), hydroxycoumarin (1 mmol) and ammonium acetate (1.5 mmol) and stirred at 110 °C under solvent-free conditions for 45 min. The reaction evolution was controlled by the TLC (hexane:ethyl acetate, 4:1). Then, boiling ethanol was added to the reaction mixture and stirred at room temperature for 15 min. After the reaction completion, the catalyst was separated by centrifuge. Finally, the reaction mixture was placed in an ice bath, which resulted in a white solid product and recrystallized from ethanol to give the pure product.

Result: The b-MOF catalyst showed very good efficiency in the synthesis of the desired compounds and can be easily recovered by centrifuge and reused at least five times without a decrease in catalytic activity.

Conclusion: In this report, a novel bi metal-organic framework (Ce0.47/Ni0.53-BTC) is synthesized via the cathodic electrosynthesis method. The synthesized b-MOF is fully characterized by several characterization methods. The catalytic activity of Ce0.47/Ni0.53-BTC is investigated in the synthesis of chromeno[4, 3-b]quinolone derivatives via one-pot four-component reaction of dimedone, aromatic aldehyde, 4-hydroxycoumarin and ammonium acetate. The reaction optimization results showed that the highest isolated yield was obtained when the reaction was performed in solvent-free conditions at 110 °C. The catalyst showed to be highly efficient in the synthesis of the desired compounds and performing the reaction utilizing various starting materials gave the products in good isolated yields, which proves the generality and the scope of the method. The catalyst could easily be recovered by centrifuge and reused at least five times without a decrease in catalytic activity.

Keywords: Metal-organic framework; aromatic aldehydes.; cathodic electrosynthesis method; chromenoquinolone; heterogeneous catalyst; multicomponent reactions.