Synthesis Of Oxazolidinones And Cyclic Carbonates Catalyzed By Amino Acids Under Supercritical Carbon Dioxide Conditions

Carbon dioxide, one of the greenhouse gases, is the earth's most abundant carbon resource. Chemical fixation of carbon dioxide is of great importance from the viewpoint of the protection of environment and carbon resources utilization. The Supercritical carbon dioxide system with the advantages of non-toxic, non-poluting, easy separation, moderate operating conditions and low cost and so on, is attracting a growing number of studies in organic reacions. Hence, two parts of researches were carried out under supercritical carbon dioxide in this paper, including the synthesis of cyclic carbonates and the synthesis of oxazolidinones.Four new polystyrene-supported amino acids: polystyrene-supported threonine (PS-Thr), polystyrene-supported tyrosine (PS-Tyr), polystyrene-supported hydroproline (PS-Hpro), and polystyrene-supported serine (PS-Ser) have been synthesized and applied to chemical fixation of carbon dioxide for the first time. Two series of experiments with PS-Thr and PS-Tyr as catalyst respectively were conducted to study the effect of the reaction conditions on the carboxylation of PO/CO2. There was no detectable decrease in the yield of PC after polystyrene-supported amino acids was used five times, indicating that this catalyst system was very stable. It was demonstrated that this catalyst system was very efficient to the carboxylation of various epoxides with CO2 under mild conditions without any solvents.A new and simple method for the cycloaddition of aziridines with carbon dioxide was developed by using naturally occurringα-amino acids as a catalyst system under mild conditions without the need of any additives. The scope of this reaction is very general, providing the corresponding products in good yields and excellent regioselectivity regardless of theα-amino acid examined and a wide variety of N-substituted aziridines employed. On the basis of the special structure of amino acid and our experimental results, a plausible reaction mechanism for the formation of oxazolidinones involving Lewis acid activation and Lewis base nucleophilic attact of the azirdines by different amino acids was proposed. In addition, we have recently disclosed that polystyrene-supported amino acids are more efficient than naturally occurringα-amino acids as a catalyst for this transformation.