[BPy]HSO4 was prepared and used as an efficient and recyclable catalyst for the one-pot three-component synthesis of α-aminophosphonates at room temperature under solvent-free conditions with good-to-excellent yields. The workup procedure is very simple, and the catalyst can be reused at least four times without any loss in catalytic activity. 1. Introduction α-Aminophosphonates are an important class of compounds because they are considered to be used as phosphorous analogs of the corresponding α-amino acids. Their diverse applications include as enzyme inhibitors [1], HIV protease [2], antibiotics [3], herbicides, fungicides, insecticides [4], as well as antithrombotic agents [5]. Various methods have been developed for the synthesis of α-aminophosphonates [6]. Recently, the synthesis of α-aminophosphonates by the one-pot three-component condensation of aldehydes, amines, and diethylphosphite or triethylphosphite has been explored in the presence of a variety of catalysts such as Cd(ClO4)2·xH2O [7], KH2PO4 [8], choline chloride·2ZnCl2 [9], H3PW12O40 [10], Zn(OAc)2·2H2O [11], [Cu(3,4-tmtppa)](MeSO4)4 [12], sulfamic acid [13], HClO4-SiO2 [14], NbCl5 [15], ytterbium perfluorooctanoate [16], nano-CeO2 [17], alum [18], Al(OTf)3 [19], thiamine hydrochloride (VB1) [20], CeCl3·7H2O [21], xanthan sulfuric acid [22], and silica sulfuric acid [23, 24]. However, some of these methods suffer from one or more drawbacks such as use of toxic catalysts which are usually nonrecoverable and organic solvents, tedious workup procedures, and the requirement of heating conditions. Thus, the development of simple, efficient, and environmentally friendly methods under mild conditions using recyclable catalysts for the synthesis of α-aminophosphonates is of current interest. Acidic ionic liquids have emerged as promising acid catalysts in replacement of conventional homogeneous and heterogeneous acidic catalysts because they are flexible, nonvolatile, noncorrosive, of low toxicity, immiscible with many organic solvents, and reusable [25]. Ionic liquids’ ([bnmim][HSO4] [26], [psmim][HSO4] [27]) catalyzed synthesis of α-aminophosphonates has also been reported. Solvent-free organic reactions make procedures simpler and prevent solvent wastes, hazards, and toxicity [28]. We report herein the acidic ionic liquid [BPy]HSO4 catalyzed one-pot synthesis of α-aminophosphonates at room temperature under solvent-free conditions. 2. Results and Discussion We herein report, a simplified and benign procedure for the preparation of the ionic liquid [BPy]HSO4 using sodium bisulphate (Scheme
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