## 3 Applications of Magnetically Recyclable Nanocatalysis (MRNCs) in Water  
Pyrrole and their derivatives are one of the most imperative modules of nitrogen-containing heterocyclic compounds as they constitute the core unit of various natural products, active pharmaceutical ingredients and medicinal chemistry [33]. [PERSON] and coworkers have reported the magnetic nanoparticle (\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\))-supported antimony (Sb) catalyst prepared by Sb containing ionic liquid via multistep synthesis procedure as depicted below (Scheme 1) [34]. The as-synthesized and well characterized MRNCs (size 30 nm, by SEM) were further employed for the synthesis of \(N\)-substituted pyrroles in moderate to excellent yield (Scheme 2; 55%-96%). This simple and facile methodology using magnetic-supported antimony ionic liquid nanocatalysts (\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)@SiO\({}_{2}\)-Sb-IL), for Clauson-Cass reaction of amines to 2,5-dimethoxy-tetrahydrofuran's worked in excellent fashion. It is interesting to note that its individual component forms such as \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\), and \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)@SiO\({}_{2}\) worked for this reaction, but better catalytic activity was found with \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)@SiO\({}_{2}\)-Sb-IL under optimized reaction conditions. Superparamagnetic nanoparticle-supported (\(S\))-diphenylprolinol trimethylsilyl ether has been employed for the asymmetric Michael-addition in aqueous media [35]. Jorgensen-Hayashi catalyst((\(S\))-diphenylproinol trimethylsilyl ether) on silica superparamagnetic nanoparticle support (MNP-JHC) was prepared by multistep synthetic procedure [35] (Figure 2). The as-synthesized and well characterized MNP-supported Jorgensen-Hayashi catalyst was employed for the asymmetric Michael addition of enolisable aldehydes to nitroalkenes in aqueous media, which gives corresponding products in moderate to good yields (up to 96%), and good enantioselectivity (up to 90% ee) (Scheme 3). **Scheme 3. ** Asymmetric Michael addition of aldehydes to nitroalkenes in aqueous media using MNP-JHC. It is important to note that the reactions successfully worked in water to deliver 85% yield of the product for the model reaction between propanal and _trans_\(\beta\)-nitrostyrene. A variety of nitroalkanes and aldehydes were investigated under the optimized reactions conditions and the corresponding products were obtained in good to excellent yields in water. Magnetite-supported Pd nanocatalysts was employed for the \(O\)-allylation of phenols with allylic acetates in aqueous media by [PERSON] _et al_. [36]; allylic ethers are important precursors for various pharmaceutical products and drug intermediates, especially as protecting group [37]. Generally, allyl ethers are obtained by Williamson-type ether synthesis, which requires strong basic metal oxides anions and active allyl halides [38]. Magnetite-supported Pd nanocatalyst was prepared by anchoring dopamine ligand under sonication, following by the addition of Pd salts under basic medium as depicted in Scheme 4. Figure 2: MNP-supported Jørgensen–Hayashi Catalyst (MNP-JHC). The spherical morphology and the size of the nano catalyst (13-38 nm) were confirmed by transmission electron microscopy (TEM) (Figure 3). The weight percentage of palladium metal was determined to be 10.23% by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analysis. The Fe\({}_{3}\)O\({}_{4}\)-Dopa-Pd nanocatalysts used for the \(O\)-allylation of phenols with allylic acetates in water under mild reaction conditions (Scheme 5). Figure 3: TEM image of [Fe\({}_{3}\)O\({}_{4}\)–dopa–Pd] catalyst. Reprinted with permission from [36]. Copyright 2012 Royal Society of Chemistry. A variety of cinnamyl acetate reacted with phenols under optimized reaction conditions to deliver the desired products in the good to excellent yield (73%-90%). The Pd metal content, determined by ICP-AES, did not leach during the reaction, which clearly indicates that the catalyst is truly in a heterogeneous form.