Green Methodologies For Synthesis Of Oxazolidinones/Thiothiazolidines Using IonicLiquids As Catalysts

In recent years, ionic liquids attracted much attention due to their unique features, such as negligible vapor pressure, non-flammability, non-combustibility, high thermal stability, relatively low viscosity, wide temperature ranges for being liquids with melting point around room temperature, high ionic conductivity, strong solubility and catalytic activity. They have been widely used in synthetic organic chemistry as solvents and catalysts as well as electrochemistry and the polymer materials. Ionic liquids are well known as salts consisting of cations and anoins, the anion and cation of ionic liquid interact with each other to form three-dimensional supramolecular network structures through several non-covalent forces, such as hydrogen bonds,π-π stacking and π-anion. The electrostatic interaction between anions and cations of ionic liquids enhance their catalytic powerful to effectively catalyze variety of organic reactions. Recently, ionic liquids have been widely used as efficient greener catalysts for synthesis of oxazolidinones/thiothiazolidines which are considered as important bioactive heterocyclic compounds.The ionic liquid-catalyzed synthesis of oxazolidinones/thiothiazolidines was investigated in this thesis, in which diethyl carbonate, epoxides, carbon disulfide, aryl carbamates, aryl amines and 2-(arylamino) alcohols were used as reactants.In the first section, a green synthetic method for synthesis of oxazolidinones through direct condensation of 2-(arylamino) alcohols with diethyl carbonate in the presence of catalytic amount of ionic liquids have been studied. The reaction of 2-(phenylamino) ethanol with diethyl carbonate was chooses as a model reaction. In order to optimize the reaction parameters, the effect of reaction time, temperature and catalysts amount were well investigated. We studied the effect of different ionic liquids on the reaction of 2-(pheny lamino) ethanol with DEC, by carry ing the reaction over a series of ionic liquids as catalysts. Excellent yields of products were obtained under the optimized reaction conditions, when using BmimOAc as a catalyst. 1HNMR spectroscopy and DFT calculation were used to determine the interaction between ionic liquid and substrates. Both anion and cation of ionic liquid cooperatively activated the substrates through hydrogen bonding.In the second section, we developed an environmentally benign, procedure for the synthesis of N-aryl-5-substituted oxazolidinones from the coupling reaction of epoxides with aryl carbamates catalyzed by ionic liquids. The effects of reaction time, reactant molar ratio, amount of catalyst and temperature were investigated. Under the optimal reaction conditions, BmimOAc exhibited efficient catalytic activity comparing with other ionic liquids. In addition, various N-aryl-5-substituted oxazolidinones were obtained in excellent yields. Besides, chiral 5-substituted oxazolidinones were synthesized by this procedure in good to excellent yields within enantiomeric excess (ee)> 99.9% starting from chiral terminal epoxides. A possible reaction mechanism was discussed according to the results given by 1H NMR spectroscopy and DFT calculations which indicates the cooperative activation by BmimOAc through hydrogen bonding with the substrates.In the third section, the one-pot conversion of aryl amines, DEC and ethylene oxide to oxazolidinones was studied. The effects of reaction temperature, time and amount of catalyst were investigated in detail. Under the optimized reaction conditions (130℃,12h, catalyst amount:10mol%), the yield of oxazolidinone was 96%. It was found that the catalytic activity of cation follows the order of 1-butyl-3-methyl-imidazolium (Bmim)> 1,2-dimethy 1-3-butyl imidazolium (Bmmim)> 1-butyl-pyridinium. Simultaneously, the catalytic activity of imidazolium based ionic liquids follows the order OAc->Cl-> Br-.In the last section, we developed a green method for the synthesis of thiothiazolidines through condensation of 2-(arylamino) alcohols with carbon disulfide over imidazolium-based ionic liquids as catalysts. We studied the effect of reaction time, temperature, substrates molar ratio and catalysts amount in details. Under the identical reaction conditions (6h,130℃,1:5 molar ratio and 10% catalyst amount), thiothiazolidine were obtained in yield of 97% with totally conversion of 2-(phenylamino) ethanol. The effects of cations and anions of ionic liquids were also studied. BmmimOAc was found to be a better catalyst for this reaction. NMR spectroscopy indicates that acetate anion of ionic liquids plays a crucial role to activate this reaction; therefore a possible reaction mechanism was discussed.