Several Applications Of Ionic Liquids In Organic Synthesis

Ionic liquids are defined as pure compounds, consisting only of cations and anions (i.e., salts), which melt at or below 100℃. Many are liquid at 25℃and are sometimes called room temperature ionic liquids or RTILs. Recently, ionic liquids (ILs) have attracted considerable interest as environmentally benign reaction media because of their many fascinating and intriguing properties. Numerous chemical reactions, including some enzymatic reactions, can be carried out in ionic liquids. An attractive feature of ionic liquids is that their solubility can be tuned readily. Therefore, phase separation from organic solvent or aqueous phase is allowed depending on the choice of cations and anions. This suggests the possibility of using these small molecular functionalized ionic liquids with special tasks (Task Specific Ionic Liquid, TSIL) as soluble supports for organic synthesis for the advantage of high-loading capacity and performing homogeneous chemistry on a relatively large scale while avoiding large excesses of reagents. In recent year, a great deal of efforts has been focused on the research of ionic liquid immobilized catalyst, reagent and ionic liquid supported synthesis (ILSS) of small molecule. In this dissertation, ionic liquid supported organic synthesis and novel method for synthesis of 1,3-disubstituted imidazole-2-thiones have been investigated and the research was divided into three parts:1. An efficient and general ionic liquid supported synthesis of cis-β-lactam library via multistep reactions have been successfully carried out in a single ionic liquid batch. The method exhibited the advantages over soluble and insoluble polymeric support strategies, such as high loading capacity, avoiding of large excesses of reagents and easy purification. Also, the products were obtained in good yields (78～83%) and purities (87～98%).2. We have developed a practical ion-supported water-soluble scavenger. aminoethylpyridinium bromide, for the purification of products in solution-phase synthesis of amides and sulfonyl amides libraries. This scavenger is easily prepared in large-scale from pyridine and 2-bromoethylamine hydrobromide, and can efficiently remove the excess acid chlorides by generating water-soluble byproduct, in which the scavenging products and the excess scavenger were separated by extraction with water and the products were obtained in excellent yields (85～93%) and purities (95～99%) . Furthermore, the new small molecule scavenger is high-loading and cost-effective, and its applications will be extended to solution-phase combinatorial chemistry.3. We have developed a novel synthesis of 1,3-disubstituted imidazole-2-thiones via a microwave-promoted reaction of imidazolium salts with potassium thioacetate or potassium thiocyanate under solvent-free conditions. Compared with the traditional methods, the present protocol is rapid, facile and efficient. It is noteworthy that the reaction could be carried out in the presence of small amount of water and that the reaction did not work when the conventional heating was used.