Abstract
In this work, biologically significant 3,3-di(indolyl)indolin-2-ones have been synthesized using a silica-coated magnetic-nanoparticle-supported 1,4-diazabicyclo[2.2.2]octane (DABCO)-derived and acid-functionalized ionic liquid as the catalytic entity. The fabricated nanocomposite catalyzes the pseudo-three-component reaction of isatins and indoles explicitly via hydrogen-bonding interactions between substrates and the catalyst. The nanocatalytic system utilizes water as the green reaction medium to obtain a library of indolinones in good to excellent yields under mild reaction conditions. Besides, the catalyst could be easily recovered from the reaction mixture through simple external magnetic forces, which enables excellent recyclability of the catalyst for successive runs without appreciable loss in catalytic activity. Hence, the outcomes of the present methodology make the nanocatalyst a potential candidate for the development of green and sustainable chemical processes.
Highlights
3,3-Di(indolyl)indolin-2-ones are one of the privileged heterocyclic molecules that possess potential biological efficacies, including spermicidal (Figure 1a),[1] anticancer,[2,3] and α-glucosidase inhibitory properties (Figure 1b).[4]
To enhance the catalytic efficiency and to make the catalytic recovery more facile, immobilization of ionic liquids has emerged as an ideal solution, which would combine the advantages of ILs and heterogeneous solid support materials.[32−34] For this, silica-coated magnetite nanoparticles (SMNPs) would be the ultimate choice for catalytic support due to their remarkable nanoscale dimensions leading to high surface area to volume ratio, magnetic recoverability, ease of functionalization, high thermal stability, and augmented dispersibility in polar reaction media
For the fabrication of the catalyst, SMNPs were chosen as the support material for immobilizing the required task-specific IL
Summary
3,3-Di(indolyl)indolin-2-ones are one of the privileged heterocyclic molecules that possess potential biological efficacies, including spermicidal (Figure 1a),[1] anticancer,[2,3] and α-glucosidase inhibitory properties (Figure 1b).[4]. As part of our continuing efforts to develop green and sustainable nanocatalysts for various organic transformations,[35,39−47] we report the design, fabrication, and characterization of a silica-coated magnetite-nanoparticlesupported DABCO-derived and acid-functionalized ionic liquid for the synthesis of bioactive 3,3-di(indolyl)indolin-2ones. The catalytic efficiency of the synthesized catalyst, DABCO-3@FSMNPs, was investigated in the formation of 3,3-di(indolyl)indolin-2-one derivatives via the pseudo-three-component one-pot reaction of indoles with isatins. No significant product yield was observed in any of the cases, justifying the utility of the DABCO-based acidic ionic liquid for the efficient synthesis of 3,3-di(indolyl)indolin-2-one derivatives. With the optimized conditions in hand, we expanded our attention toward a variety of indoles and isatins to synthesize a library of 3,3-di(indolyl)indolin-2-ones with 50 mg of the DABCO-3@FSMNP catalyst under aqueous conditions at 90 °C in 2 h (Table 2). The present catalyst utilizes comparable reaction conditions and proves its supremacy in terms of effortless magnetic recoverability and reusability up to eight cycles
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