Study On The Cyclization Reactions Of Oxiranes And Imines Via Lewis Acid Catalyzed C-C Bond Cleavage

Oxiranes widely exist in thousands of natural products and medical molecules. Therefore, it is very important to develop some new and efficient methods for derivatization and transformation of oxiranes. Our group got breakthrough in the field of Lewis acid-promoted C-C bond cleavage of oxirane. On the basis of results gotten by the whole group, my subject is to capture carbonyl ylides with imines. This thesis mainly consists of two parts.In the first part, the reaction of nitrone and oxiranes with only one Electron-withdrawing group was tested. Unfortunately, it proves heterolysis of C-O bond. Then we developed the [3+2] cycloaddition of imines and oxiranes with two Electron-withdrawing groups. Ni(C104)2·6H2O could catalyze the reaction efficiently leading to substituted oxazolidine with high diastereoselectivity in presence of nitrogenous ligands. One acetyl was successfully removed for cycloaddition product under base conditions. Enantioenriched oxiranes were prapered to study the mechanism. A racemic cycloaddition product was obtained, indicating reaction mechanism is stepwise one rather than concerted one.In the second part, we researched asymmetric reaction of aryl oxiranyl diketones and imines. We synthesized and tested a series of oxazoline ligands and pyridine N-O ligands. Finally some good results were obtained. Up to now, the research is still under way in our group.