CuO Nanopatricles as a Recyclable Heterogeneous Catalyst for the Synthesis of some Thiazolines and Imidazolines under Solvent Free Conditions

Recently, heterogeneous catalysts have become attractive from both economic and industrial points of view as compared to homogeneous catalysts. In general, nanoscale heterogeneous catalysts offer higher surface area and lower coordinating sites, which are responsible for the higher catalytic activity [1]. Furthermore, heterogeneous catalysis has the advantage of high atom-efficiency, easy product purification, and reusability of the catalyst. Copper oxide nanoparticels (NP-CuO), titanium oxide nanoparticels (NP-TiO2) and nickel oxide (NP-NiO) nanoparticels are useful example of reusable heterogeneous catalysts, which has been studied in few recent years. NP-CuO, NP-TiO2 and NP-NiO are easily prepared from several methods such as hydrothermal, solvothermal, sol-gel and sonochemsitry methods [2]. Copper oxide (CuO) has been received extensive investigations for its prospective applications in many fields. 2-thiazolines and 2-imidazolines are very important active molecules due to their extensive applications in chemistry, biochemistry and pharmacology [3]. These heterocycles are found in the structures of many biologically active natural products [4]. They also exhibit several pharmaceutical activities such as antialzheimer [5], antihypertensive [6], anticancer [7], antitumor [8], antidiabetic [9], antidepressive [10] and anti HIV-1 [11]. They are also known as important intermediates in organic transformations [12]. Many methodologies have been developed for the preparation of 2-substituted thiazolines and imidazolines from different precursors such as esters [16], carboxylic acids [13], amides [14], aziridines [15], aldehydes [16] and nitriles [17]. Various reaction conditions and a variety of homogeneous and heterogeneous catalysts have been applied for this purpose. Most of them involve one or more disadvantages including harsh reaction conditions, long reaction times, low yields of products, the use of stoichiometric amounts of catalysts, the use of excess amounts of reagents and relatively expensive reagents and/or toxic solvents. Furthermore, in the case of nitrile compounds, the use of highly toxic cyanide is necessary for their preparation. So, the development of an efficient, simple and environmentally benign catalytic procedure for the synthesis of these heterocycles is still in high demand. In the paper, we would like to report the use of copper oxide nanoparticels (NP-CuO) catalyst in the synthesis of 2-substituted thiazolines and imidazolines (Scheme 1