Bifunctional PEG/NH2 silica-coated magnetic nanocomposite: An efficient and recoverable core-shell-structured catalyst for one pot multicomponent synthesis of 3-alkylated indoles via Yonemitsu-type condensation

摘要

In the present work, a new, green and recyclable bifunctional PEG/NH2 silica-coated Fe3O4 nanoparticle was prepared and successfully characterized by FT-IR spectroscopy, scanning electron microscopy (SEM), X-ray powder Diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM) and Brunauer-Emmett-Teller (BET) analysis. The catalytic activity of this dual function silica-iron oxide hybrid nanocomposite, Fe3O4@SiO2-PEG/NH2, was successfully tested in the straightforward one-pot synthesis of groups of biologically active 3-alkylated indoles via three-component reaction between indole, aromatic aldehydes, and C-H activated acids. The results exhibited that a synergistic effect existed between the PEG and base groups. PEG units not only increase the reactivity of carbonyl groups by hydrogen bonding but also these hydrophilic groups accelerate the reaction by absorption of producing water as by-product. The significant features of the present protocol that enhance its effectiveness from an economic as well as environmental benefits are high yields, easy work-up procedure, short reaction times, high atom-economy, and recyclability of the catalyst. (C) 2018 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.